GENERAL MACHINIST PRACTICAL I &

GENERAL MACHINIST
THEORY
VOCATIONAL EDUCATION
HIGHER SECONDARY - SECOND YEAR
A Publication under
Government of Tamilnadu
Distribution of Free Textbook Programme
( NOT FOR SALE )
Untouchability is a sin
Untouchability is a crime
Untouchability is inhuman
TAMILNADU
TEXTBOOK CORPORATION
College Road, Chennai - 600 006.
©
Government of Tamilnadu
First Edition - 2011
Chairperson
Dr. R. RAJKUMAR,
Head of the Department ( Mechanical )
AMK Polytechnic College,
Sembarambakkam, Chennai - 602 103.
Authors
G. JAYAKUMAR JESUDOSS,
Vocational Teacher,
Dharmamurthi Rao Bahadur Calavala Cunnan Chetty’s
Hindu Higher Secondary School,
Thiruvallur - 602 001.
C. RAVIVARMAN
A. VELAYUTHAM
Vocational Teacher,
Govt. Boys Higher Secondary School,
Nattrampalli,
Vellore Dist - 635 852.
Vocational Teacher,
Govt. Higher Secondary School,
Nemili,
Vellore Dist - 631 051.
B. PRABHAKARAN
N. PALANIVELU
Vocational Teacher,
Govt. Boys Higher Secondary School,
Vandavasi,
Thiruvannamalai Dist-604 408.
Vocational Teacher,
Govt. Boys Higher Secondary School,
Arni,
Thiruvannamalai Dist - 632 301.
This book has been prepared by the Directorate of School Education on behalf of the
Government of Tamilnadu
This book has been printed on 60 GSM paper
Printed by Web Offset at :
INDEX
Sl. No.
Title
Page No.
1.
Lathe
1
2.
Drilling machine
43
3.
Shaping machine
70
4.
Grinding machine
94
5.
Milling machine
119
6.
Hydraulic equipments
148
7.
Electrical equipments
173
8.
Welding
181
9.
CNC Machines
201
10.
Machine tool maintenance
215
iii
1. LATHE
1.1 Introduction
Lathe is considered as one of the oldest machine tools and is widely used in industries.
It is called as mother of machine tools. It is said that the first screw cutting lathe was
developed by an Englishman named Henry Maudslay in the year 1797. Modern high speed,
heavy duty lathes are developed based on this machine.
The primary task of a lathe is to generate cylindrical workpieces. The process of
machining a workpiece to the required shape and size by moving the cutting tool either
parallel or perpendicular to the axis of rotation of the workpiece is known as turning. In this
process, excess unwanted metal is removed. The machine tool useful in performing plain
turning, taper turning, thread cutting, chamfering and knurling by adopting the above
method is known as lathe. Fig 1.1 shows turning operation.
Chuck
Work
Cutting tool
Direction of feed
Fig 1.1 Turning
1
Carriage
Live centre
Spindle
Bed
Fig 1.2 Lathe - Parts
Compound rest
Toolpost
Cross-slide
Thread chasing dial
Feed rod
Leadscrew
Half-nut lever
Rack
Tailstock
Tailstock spindle
Deadcentre
1.2 Main parts of a lathe
Every individual part performs an important task in a lathe. Some important parts of a
lathe are listed below
1. Bed
2. Headstock
3. Spindle
4. Tailstock
5. Carriage
a. Saddle
b. Apron
c. Cross-slide
d. Compound rest
e. Compound slide
f. Tool post
6. Feed mechanism
7. Leadscrew
8. Feed rod
9. Thread cutting mechanism
Fig 1.2 shows the different parts of a lathe.
1.2.1 Bed
Bed is mounted on the legs of the lathe which are bolted to the floor. It forms the base
of the machine. It is made of cast iron and its top surface is machined accurately and
precisely. Headstock of the lathe is located at the extreme left of the bed and the tailstock at
the right extreme. Carriage is positioned in between the headstock and tailstock and slides
on the bed guideways.
The top of the bed has flat or ‘V’ shaped guideways. The tailstock and the carriage
slides on these guideways. Inverted ‘V’ shaped guideways are useful in better guide and
accurate alignment of saddle and tailstock. The metal burrs resulting from turning operation
automatically fall through. Flat bed guideways can be found in older machine tools. It is
useful in heavy machines handling large workpieces. But then the accuracy is not high.
3
1.2.2 Headstock
Headstock is mounted permanently on the inner guideways at the left hand side of
the leg bed. The headstock houses a hollow spindle and the mechanism for driving the spindle
at multiple speeds. The headstock will have any of the following arrangements for driving
and altering the spindle speeds
(i)
(ii)
(iii)
Stepped cone pulley drive
Back gear drive
All gear drive
1.2.3 Spindle
The spindle rotates on two large bearings housed on the headstock casting. A hole
extends through the spindle so that a long bar stock may be passed through the hole. The
front end of the spindle is threaded on which chucks, faceplate, driving plate and catch plate
are screwed. The front end of the hole is tapered to receive live center which supports the
work. On the other side of the spindle, a gear known as a spindle gear is fitted. Through this
gear, tumbler gears and a main gear train, the power is transmitted to the gear on the
leadscrew. The construction of a lathe spindle is shown in Fig 1.3
Hole
Spindle
Threaded end
Taper sleeve
Live centre
Fig 1.3 Spindle
1.2.4 Tailstock
Tailstock is located on the inner guideways at the right side of the bed opposite to the
headstock. The body of the tailstock is bored and houses the tailstock spindle or ram. The
spindle moves front and back inside the hole. The spindle has a taper hole to receive the
dead centre or shanks of tools like drill or reamer. If the tailstock handwheel is rotated in
the clockwise direction, the spindle advances. The spindle will be withdrawn inside the
hole, if the handwheel is rotated in anti-clockwise direction.
4
To remove the dead centre or any other tool from the spindle, the handwheel is
rotated in anticlockwise direction further. The movement of the spindle inside the hole may
be locked by operating the spindle clamp located on top of the tailstock.In order to hold
workpieces of different lengths, the tailstock can be locked at any desired position on the
lathe bed. Tailstock clamping bolts and clamping pates are used for this purpose.
Tailstock is designed to function as two units-the base and the body. The base of the
tailstock is clamped to the bed. The body is placed on the base and can be made to slide
sidewards-perpendicular to the bed guideways upto a certain distance. Fig 1.4 shows a
tailstock.
Spindle
Clamp
Bush
Barrel
Screw
Dead centre
Handwheel
Setover
screw
Tailstock
clamping
bolt
Bed
Fig 1.4 Tailstock
The uses of tailstock
1. It supports the other end of the long workpiece when it is machined between
centres.
2. It is useful in holding tools like drills, reamers and taps when performing drilling,
reaming and tapping.
3. The dead centre is off set by a small distance from the axis of the lathe to turn
tapers by set over method.
4. It is useful in setting the cutting tool at correct height aligning the cutting edge with
lathe axis.
5
1.2.5 Carriage
Carriage is located between the headstock and tailstock on the lathe bed guideways.
It can be moved along the bed either towards or away from the headstock. It has several
parts to support, move and control the cutting tool. The parts of the carriage are :
a) saddle
b) apron
c) cross-slide
d) compound rest
e) compound slide
f) tool post
Different parts of a carriage are shown in Fig 1.5
Toolpost
Compound rest
Compound slide
Cross-slide
Cross feed handwheel
Chasing dial
Saddle
Apron
Longitudinal
feed
handwheel
Fig 1.5 Carriage
Saddle:
It is an “H” shaped casting. It connects the pair of bed guideways like a bridge. It
fits over the bed and slides along the bed between headstock and tailstock. The saddle or
the entire carriage can be moved by providing hand feed or automatic feed.
6
Cross slide:
Cross-slide is situated on the saddle and slides on the dovetail guideways at right
angles to the bed guideways. It carries compound rest, compound slide and tool post. Cross
slide handwheel is rotated to move it at right angles to the lathe axis. It can also be power
driven. The cross slide hand wheel is graduated on its rim to enable to give known amount of
feed as accurate as 0.05mm.
Compound rest:
Compound rest is a part which connects cross slide and compound slide. It is mounted
on the cross-slide by tongue and groove joint. It has a circular base on which angular
graduations are marked. The compound rest can be swiveled to the required angle while
turning tapers. A top slide known as compound slide is attached to the compound rest by
dove tail joint. The tool post is situated on the compound slide.
Tool post:
This is located on top of the compound slide. It is used to hold the tools rigidly. Tools
are selected according to the type of operation and mounted on the tool post and adjusted
to a convenient working position. There are different types of tool posts and they are:
1. Single screw tool post
2. Four bolt tool post
3. Four way tool post
4. Open side tool post
Single screw tool post
The tool is held by a screw in this toolpost. It consists of a round bar with a slotted
hole in the centre for fixing the tool by means of a setscrew. A concave ring and a convex
rocker are used to set the height of the tool point at the right position. The tool fits on the
flat top surface of the rocker. The tool post is not rigid enough for heavy works as only one
clamping screw is used to clamp the tool. A single screw toolpost is illustrated in Fig 1.6
Four way tool post
This type of tool post can accommodate four tools at a time on the four open sides of
the post. The tools are held in position by separate screws and a locking bolt is located at
the centre. T h e required tool may be set for machining by swiveling the tool post.
Machining can be completed in a shorter time because the required tools are pre-set.
7
Toolpost screw
Toolpost body
Tool
Concave ring
Convex rocker
Fig 1.6 Single screw toolpost
1.2.6 Feed mechanism
There are several mechanisms to make the carriage and crose-slide move
automatically and to change the direction of their movement. Some important mechanisms
are dealt with as follows.
Tumbler gear arrangement
Tumbler gears are located in the headstock just below the spindle gear. For the
purpose of moving the carriage towards or away from the headstock, this mechanism along
with feed rod or leadscrew is used.
Tumbler gears are two small pinions mounted on a bracket. This bracket is pivoted
about the axis of the stud gear. The position of the bracket can be arranged in three different
stages namely i) neutral ii) forward & iii) reverse. Hence, the direction of rotation of the
leadscrew and the feed rod is reversed.
Neutral position
When the bracket is held in neutral position, both the tumbler gears A and B stand
disengaged from the spindle gear and main gear train. And so carriage will not get any
movement.
8
Forward position
When the bracket is arranged in the forward position as shown in the diagram, only
one of the tumbler gears(B) comes between the spindle gear and the main gear train. In that
position, the leadscrew or the feed rod rotates in the direction of the headstock spindle
rotation. The carriage moves towards the headstock providing the cutting tool with
longitudinal feed.
Reverse position
When the bracket is arranged in the reverse position, both the tumbler gears come in
contact between the spindle gear and the main gear train. The carriage moves towards the
tailstock to give the tool the longitudinal feed in the opposite direction.
Tumbler gear arrangement is shown in Fig 1.7
Spindle gear
Tumbler
gears
A
B
Bracket
Lever
Intermediate
gears
Gear on the
leadscrew
Forward position
Reverse position
Fig 1.7 Tumbler gear arrangement
9
Apron Mechanism:
Apron is attached to the carriage and hangs over the front side of the lathe bed. It is
useful in providing power and hand feed to both carriage and cross-slide. It is also used to
provide power feed to the carriage during thread cutting through two half nuts. The
construction of apron is shown in Fig 1.8
Feed selection lever
Half nut lever
Rack
Leadscrew
Carriage
handwheel
Feed rod
Worm gear
Worm
Fig 1.8 Apron of a lathe
Construction
Power is transmitted from the spindle to the leadscrew and feed rod through the
spindle gear and tumbler gear arrangement. A worm is mounted on the feed rod by a sliding
key. The worm meshes with a worm gear on whose axis another gear G1 is attached. Gear
G1 is attached to a small gear G2 by a bracket as shown in the diagram. Gear G4 is
positioned to be in mesh with the rack gear always. Another gear G3 is mounted on the same
axis of gear G4. The carriage handwheel meant for longitudinal feed is attached to the gear
G5 on the same axis. The gears G3 and G5 are always in mesh. The gear G6 is attached to
the cross slide screw.
The feed selection lever can be kept in neutral, up and down positions to obtain the
following movements.
1. Hand feed and power feed to the carriage
2. Hand feed and power feed to the cross slide
10
Hand feed to the carriage
Feed selection lever is kept in neutral position and the carriage handwheel is rotated.
The gear G4 attached to the rack gets rotation through the gears G5 and G3. The carriage
moves longitudinally.
Power feed to the carriage
When feed selection lever is kept in up position (U), the gear G2 will mesh with gear
G3. Gear G4 gets rotation through gear G3 and the carriage gets automatic (power) feed.
Hand feed to the cross slide
Feed selection lever is kept in neutral position. The cross slide will move on rotation
of the cross slide handwheel.
Power feed to the cross slide
When the feed selection lever is kept in down position (D), gear G2 will be in contact
with gear G6. The rotation of G6 will make the cross slide screw also to rotate and the
cross-slide moves automatically.
Power feed to the carriage for thread cutting
When the two half nuts in the apron are made as one unit, leadscrew makes the
carriage to move automatically and cut threads of required pitch value.
1.2.7 Leadscrew
The leadscrew is a long threaded shaft used as master screw. It is brought into
operation during thread cutting to move the carriage to a calculated distance. Mostly
leadscrews are Acme threaded.
The leadscrew is held by two bearings on the face of the bed. A gear is attached to
the lead screw and it is called as gear on leadscrew. A half nut lever is provided in the apron
to engage half nuts with the leadscrew.
Leadscrew is used to move the carriage towards and away from the headstock
during thread cutting. The direction of carriage movement depends upon the direction of
rotation of the leadscrew.When the leadscrew is kept stationary, the half nuts are engaged
with the leadscrew to keep the carriage locked at the required position.
11
1.2.8 Feed rod
Feed rod is placed parallel to the leadscrew on the front side of the bed. It is a long
shaft which has a keyway along its length. The power is transmitted from the spindle to the
feed rod through tumbler gears and a gear train. It is useful in providing feed movement to
the carriage except for thread cutting and to move cross-slide. A worm mounted on the feed
rod enables the power feed movements.
1.3 Spindle mechanism
The spindle is located in the headstock and it receives the driving power from the
motor. The spindle speed should be changed to suit different machining conditions like type
of material to be cut, the diameter and the length of the work, type of operation, the type of
cutting tool material used, the type of finish desired and the capacity of the machine. In
order to change the spindle speeds, any one of the following methods are employed.
1. Step cone pulley drive
2. Back geared drive
3. All geared drive
1.3.1. Step cone pulley drive
Spindle
It is simple in construction. The
belt is arranged on the four different steps
of the cone pulley to obtain four
different speeds.
A step cone pulley is attached
with the spindle contained within the
headstock casting. The cone pulley has
four steps (A, B, C & D). Another cone
pulley having four steps (E, F, G and H)
is placed parallel to the spindle cone
pulley. Both the cone pulleys are
connected by a flat belt. The belt can be
arranged between the steps A & H, B &
G, C & F and D & E. The cone pulley at
the bottom is connected to the electric
motor by a ‘V’belt. So the cone pulley
at the bottom rotates at a particular
speed.
Step cone
pulley
Flat belt
Step cone
pulley
‘V’ belt
Electric
motor
Fig 1.9 Step cone pulley drive
12
The belt is arranged on any of the four steps to obtain different spindle speeds. The
spindle speed is increased if the belt is placed on the smaller step of the driven pulley. The
spindle speed will be maximum when the belt is arranged between A & H and the speed will
be minimum when the belt is arranged between D & E. Step cone pulley drive is illustrated in Fig 1.9
1.3.2 Back gear mechanism
Back gear mechanism is housed within the headstock of the lathe. A step cone pulley
having steps ABCD and a small pinion ‘P’ are mounted on the spindle and rotates freely on
it. The gear ‘S’ is keyed to the headstock spindle. So, the spindle will rotate only when the
gear ‘S’ rotates.
The step conepulley ABCD and the gear ‘S’ can be kept seperately or made as one
unit with the help of a pin ‘T’. When the pin is disengaged, the conepulley along with the
gear P will rotate freely on the spindle and the spindle will not rotate. There is another shaft
parallel to the spindle axis having back gears Q and R mounted on it. These back gears can
be made to mesh with gears P and S or kept disengaged from them. The spindle can get
drive either from the cone pulley or through back gears.
Back gears
Pin
Spindle
Belt
Fig 1.10 Back gear drive
13
Drive from step conepulley
When the spindle gets drive from the conepulley, the backgears Q and R are
disengaged from the gears P and S. The pin ‘T’ is engaged with conepulley. The belt can be
arranged on the steps A,B,C or D to get four different direct speeds for the spindle.
Back gear drive is illustrated in Fig 1.10
Drive through back gears
Back gears Q and R are engaged with gears P and S. The pin ‘T’ is disengaged from
the conepulley to make the conepulley and the spindle separate units. When the conepulley
gets drive through the belt, the power is transmitted through the gears P,Q and R to the gear
S. Because of number of teeth on these gears, the spindle rotates at slower speeds. By
arranging the belt on the different steps of the conepulley, four different spindle speeds are
obtained.
Uses of back gear arrangement
1. The spindle gets four direct speeds through the conepulley and four slower speeds
through the back gears.
2. Slower speeds obtained by this arrangement are useful when turning on larger
workpieces and cutting coarse threads.
1.3.3 All geared headstock
Modern lathes are equipped with all geared headstocks to obtain different spindle
speeds quickly. Casting of the all geared headstock has three shafts(1,2& 3) mounted within
it. The intermediate shaft(2) has got three gears D, E and F as a single unit and rotate at the
same speeds. The splined shaft(1) which is above the intermediate shaft has got three gears
A, B and C mounted on it by keys. These three gears can be made to slide on the shaft with
the help of a lever. This movement enables the gear A to have contact with the gear D or the
gear B with gear E or the gear C with the gear F.
Likewise the spindle shaft(3) which is also splined has three gears G, H and I. With
the help of a lever, these three gears can be made to slide on the shaft. This sliding movement enables the gear G to have contact with gear D or the gear H with the gear E or the
gear I with the gear F. By altering the positions of the six gears namely A, B, C, G, H and I
the following arrangements can be made within the headstock. Nine different spindle speeds
are obtained. All geared drive is shown in Fig 1.11
14
Pulley
Spindle
Fig 1.11 All geared drive
The gear combinations are
1.
A
D
----- x ----D
G
4.
B
D
----- x ----E
G
7.
C
D
----- x ----F
G
2.
A
E
----- x ----D
H
5.
B
E
----- x ----E
H
8.
C
E
----- x ----F
H
3.
A
F
----- x ----D
I
4.
B
F
----- x ----E
I
9.
C
F
----- x ----F
I
1.4 Types of lathe
Various designs and constructions of lathe have been developed to suit different
machining conditions and usage. The following are the different types of lathe
1. Speed lathe
a. Woodworking lathe
b. Centering lathe
c. Polishing lathe
d. Metal spinning lathe
15
2. Engine lathe
a. Belt driven lathe
b. Individual motor driven lathe
c. Gear head lathe
3. Bench lathe
4. Tool room lathe
5. Semi automatic lathe
a. Capstan lathe
b. Turret lathe
6. Automatic lathe
7. Special purpose lathe
a. Wheel lathe
b. Gap bed lathe
c. ‘T’ lathe
d. Duplicating lathe
1.4.1 Speed lathe
Spindle of a speed lathe operates at very high speeds (approximately at a range of
1200 to 3600 rpm) and so it is named so. It consists of a headstock, a tailstock, a bed and
a toolslide only. Parts like leadscrew, feed rod and apron are not found in this type of lathe.
1. Centering lathes are used for drilling center holes.
2. The woodworking lathes are meant for working on wooden planks.
3. Metal spinning lathes are useful in making tumblers and vessels from sheet metal.
4. Polishing of vessels is carried out in polishing lathe.
1.4.2 Engine lathe or centre lathe
Engine lathes are named so because the early lathes were driven by steam engines.
As the turning operations are performed by holding the workpiece between two centers, it is
also known as centre lathe. Engine lathes are widely used in industries. It consists of parts
like headstock, tailstock and carriage. Parts like leadscrew and feed rod which are useful in
providing automatic feed are also found in this type of lathe.
1.4.3 Bench lathe
Bench lathe is a small lathe generally mounted on a bench. It consists of all the parts
of a engine lathe. It is used for small works like machining tiny and precise parts and parts of
measuring instruments.
16
1.4.4 Tool room lathe
A tool room lathe has similar features of an engine lathe but is accurately built and
has wide range of spindle speeds to perform precise operations and different feeds. It is
costlier than a centre lathe. This is mainly used for precision works like manufacturing tools,
dies, jigs, fixtures and gauges.
1.4.5 Semi automatic lathe
Turret and Capstan lathes are known as semi-automatic lathes. These lathes are used
for production work where large quantities of identical workpieces are manufactured. They
are called semi-automatic lathes as some of the tasks are performed by the operators and
the rest by the machines themselves.
A semi skilled operator can do this at low cost and at shorter time. So, the cost of
production is reduced. There are two tool posts in the machine namely four way tool post
and rear tool post. Four tools can be mounted on the four way tool post and parting tool is
mounted on the rear tool post. The tailstock of an engine lathe is replaced by a hexagonal
turret. As many tools may be fitted on the six sides of the turret, different types of
operations can be performed on a workpiece without resetting of tools. The toolheads of a
turret lathe and a capstan lathe are illustrated in Fig1.12 & Fig.1.13
Turret
Saddle
Bed
Handwheel
Fig 1.12 Toolhead of a
turret lathe
1.4.6 Automatic lathe
Automatic lathes are operated with complete automatic control. They are high speed,
mass production lathes. An operator can look after more than one automatic lathe at a time.
17
1.4.7 Special purpose lathe
Special purpose lathes are used for special purposes and for jobs, which cannot be
accommodated and conveniently machined on a standard lathe. Wheel lathe, ‘T’ lathe,
duplicating lathe are some examples of special purpose lathe.
1.4.8 Differences between an engine lathe and a turret & capstan lathe
Turret & Capstan lathe
Engine lathe
1. There is only one tool post
1. There are two tool posts - fourway
tool post and rear tool post
2. Tailstock is located at the right side
of the bed
2. Tailstock is replaced by an hexagonal
tool head called turret
3. Only one cutting tool can be held in
the tailstock
3. A minimum of six tools can be held in
the turret
4. No provision to control the tool
movement (feed) automatically
4. Turret movement can be controlled
automatically
5. Only one tool can be put into
machining at a time. Tools have to be
set everytime according to the
operation to be performed
5. More tools can be set on the turret
and each of them can be set at the work
one by one automatically
6. Setting of tools will take more time
6. Setting of cutting tool is easy
7. A skilled operator is necessary to
work on the machine
7. After the initial settings are made, a
semi-skilled operator can operate the
machine
8. The machine has to be stopped to
change the tool
8. Tools can be indexed even when the
machine is on
9. The production cost is high
9. Production cost is reduced as the
rate of production is more
10. Motors with 3 to 5 HP are used
10. Motors with 15 HP are used
18
1.4.9 Differences between a turret lathe and a capstan lathe
Turret lathe
Capstan lathe
1. Turret tool head is directly fitted on
the saddle and both of them appear like
one unit.
1. Turret head is mounted on a slide
called ram which is mounted on the
saddle
2. Saddle is moved to provide feed to
the tool
2. To provide feed to the tool, saddle is
locked at a particular point and the ram
is moved
3. It is difficult to move the saddle for
feed
3. It is easy to move the ram for feed
4. As the saddle can be moved along the
entire length of the bed, it is suitable for
longer workpieces
4. As the movement of the ram is
limited, it is suitable for machining
shorter workpieces only
5. To index the turret tool head, a
clamping lever is released and the turret
is rotated manually
5. When the handwheel for the ram is
reversed, the turret tool head is indexed
automatically
6. Limit dogs are used to control the
distance of tool movement
6. To control the distance of tool
movement, feed stop screws are
provided at the rear side of the turret
7. Some turret lathes have the facility of
moving the turret at right angles to the
lathe axis
7. No such facility
8. Heavy and sturdy
8. Lighter in construction
9. Suitable for machining heavy and
large workpieces
9. Only small and light workpieces are
machined
10. Machining can be done by providing
more depth of cut and feed
10. Only limited amount of feed and
depth of cut are provided for machining
19
Ram
Turret
Feed controlling
screws
Saddle
Bed
Handle
Fig 1.13 Toolhead of a capstan lathe
1.5 Size of a lathe
The size of a lathe is specified by the following points
1. The length of the bed
2. Maximum distance between live and dead centres.
3. The height of centres from the bed
4. The swing diameter
The swing diameter over bed - It refers to the largest diameter of the
work that will be rotated without touching the bed
The swing diameter over carriage - It is the largest diameter of the work that
will revolve over the saddle.
5. The bore diameter of the spindle
6. The width of the bed
7. The type of the bed
8. Pitch value of the lead screw
9. Horse power of the motor
10. Number and range of spindle speeds
11. Number of feeds
12. Spindle nose diameter
13. Floor space required
14. The type of the machine
20
1.6 Work holding devices used in a lathe
The work holding devices are used to hold and rotate the workpieces along with the
spindle. Different work holding devices are used according to the shape, length, diameter
and weight of the workpiece and the location of turning on the work. They are
1. Chucks
2. Face plate
3. Driving plate
4. Catchplate
5. Carriers
6. Mandrels
7. Centres
8. Rests
1.6.1 Chucks
Workpieces of short length, large diameter and irregular shapes, which can not be
mounted between centres, are held quickly and rigidly in chuck.There are different types of
chucks namely, Three jaw universal chuck, Four jaw independent chuck, Magnetic chuck,
Collet chuck and Combination chuck.
Three jaw self-centering chuck
The three jaws fitted in the three slots may be made to slide at the same time by an
equal amount by rotating any one of the three pinions by a chuck key.This type of chuck is
suitable for holding and rotating regular shaped workpieces like round or hexagonal rods
about the axis of the lathe. Workpieces of irregular shapes cannot be held by this chuck.
Body
Key hole
Jaw
Jaws
Fig 1.14 Three jaw chuck
21
The work is held quickly and easily as the three jaws move at the same time. Fig
1.14 shows a three jaw chuck
Four jaw independent chuck
There are four jaws in this chuck. Each jaw is moved independently by rotating a
screw with the help of a chuck key. A particular jaw may be moved according to the shape
of the work. Hence this type of chuck can hold woks of irregular shapes. But it requires
more time to set the work aligned with the lathe axis. Experienced turners can set the work
about the axis quickly. Concentric circles are inscribed on the face of the chuck to enable
quick centering of the workpiece. A four jaw chuck is illustrated in Fig 1.15
Concentric circular
lines
Key hole
Jaws
Jaw
Body
Fig 1.15 Four jaw chuck
Magnetic chuck
Magnets
The holding power of this
chuck is obtained by the magnetic flux
radiating from the electromagnet
placed inside the chuck. Magnets are
adjusted inside the chuck to hold or
release the work. Workpieces made
of magnetic material only are held in
this chuck. Very small, thin and light
works which can not be held in a ordinary chuck are held in this chuck.
Fig 1.16 shows a magnetic chuck
Body
Fig 1.16 Magnetic chuck
22
Collet chuck
Collet chuck has a cylindrical bushing known as collet. It is made of spring steel
and has slots cut lengthwise on its circumference. So, it holds the work with more grip.
Collet chucks are used in capstan lathes and automatic lathes for holding bar stock in production work.
A collet chuck is illustrated in Fig 1.17
Jaws
Body
Fig 1.17 Collet chuck
1.6.2 Face plate
Faceplate is used to hold large, heavy and irregular shaped workpieces which can
not be conveniently held between centres. It is a circular disc bored out and threaded to fit
to the nose of the lathe spindle. It is provided with radial plain and ‘T’ – slots for holding the
work by bolts and clamps.
Fig 1.18 illustrates a face plate.
Fig 1.18 Face plate
23
1.6.3 Driving plate
The driving plate is used to drive a workpiece when it is held between centres. It is a
circular disc screwed to the nose of the lathe spindle. It is provided with small bolts or pins
on its face. Workpieces fitted inside straight tail carriers are held and rotated by driving
plates. Fig 1.19 shows a driving plate.
Driving pin
Fig 1.19 Driving plate
1.6.4 Catch plate
When a workpiece is held between centres, the catch plate is used to drive it. It is a
circular disc bored and threaded at the centre. Catch plates are designed with ‘U’ – slots or
elliptical slots to receive the bent tail of the carrier. Positive drive between the lathe spindle
and the workpiece is effected when the workpiece fitted with the carrier fits into the slot of
the catch plate.
Fig 1.20 illustrates a catch plate.
Fig 1.20 Catch plate
24
1.6.5 Carrier
When a workpiece is held and machined between centres, carriers are useful in transmitting the driving force of the spindle to the work by means of driving plates and catch
plates. The work is held inside the eye of the carrier and tightened by a screw. Carriers are
of two types and they are :
1. Straight tail carrier
2. Bent tail carrier
Straight tail carrier is used to drive the work by means of the pin provided in the
driving plate. The tail of the bent tail carrier fits into the slot of the catch plate to drive the
work. The types of carriers are illustraed in Fig. 1.21
Screw
Eye
Bent tail carrier
Straight tail carrier
Tail
Fig 1.21 Carriers
1.6.6 Mandrel
A previously drilled or bored workpiece is held on a mandrel to be driven in a lathe
and machined. There are centre holes provided on both faces of the mandrel. The live centre
and the dead centre fit into the centre holes. A carrier is attached at the left side of the
mandrel. The mandrel gets the drive either through a catch plate or a driving plate. The
workpiece rotates along with the mandrel. There are several types of mandrels and they are:
1. Plain mandrel
2. Step mandrel
3. Gang mandrel
5. Collar mandrel
6. Cone mandrel
7. Expansion mandrel
25
Plain mandrel
The body of the plain mandrel is slightly tapered to provide proper gripping of the
workpiece. The taper will be around 1 to 2mm for a length of 100mm. It is also known as
solid mandrel. It is the type mostly commonly used and has wide application. A plain
mandrel is illustrated in Fig 1.22
Fig 1.22 Plain mandrel
Gang mandrel
It has a fixed collar at one end and a movable collar at the threaded end. This mandrel is used to hold a set of hollow workpieces between the two collars by tightening the nut.
Fig 1.23 shows a gang mandrel.
Workpieces
Fixed collar
Movable collar
Nut
Fig 1.23 Gang mandrel
Screwed mandrel
It is threaded at one end and a collar is attached to it. Workpieces having internal
threads are screwed on to it against the collar for machining. Fig 1.24 shows a screwed
mandrel.
Fixed collar
Thread
Fig 1.24 Threaded mandrel
26
Cone mandrel
It consists of a solid cone attached to one end of the body and a sliding cone, which
can be adjusted by turning a nut at the threaded end. This type is suitable for driving workpieces
having different hole diameters. A cone mandrel is illustrated in Fig 1.25
Fixed cone
Sliding cone
Nut
Fig 1.25 Cone mandrel
1.6.7 Centres
Centres are useful in holding the work in a lathe between centres. The shank of a
centre has Morse taper on it and the face is conical in shape. There are two types of centres
namely
(i) Live centre
(ii) Dead centre
The live centre is fitted on the headstock spindle and rotates with the work. The
centre fitted on the tailstock spindle is called dead centre. It is useful in supporting the other
end of the work. Centres are made of high carbon steel and hardened and then tempered.
So the tip of the centres are wear resistant. Different types of centres are available according to the shape of the work and the operation to be performed. They are
1. Ordinary centre
2. Ball centre
3. Half centre
4. Tipped centre
5. Pipe centre
6. Revolving cenrte
Fig 1.26 Centre
7. Inserted type centre
An ordinary centre is shown in Fig. 1.26.
27
Fig. 1.27 shows the use of different work holding devices.
Driving plate
Work
Carrier
Mandrel
Dead centre
Live centre
Fig 1.27 Holding a work between centres
1.6.8 Rests
A rest is a mechanical device to support a long slender workpiece when it is turned
between centres or by a chuck. It is placed at some intermediate point to prevent the
workpiece from bending due to its own weight and vibrations setup due to the cutting force.
There are two different types of rests
1. Steady rest
2. Follower rest
Steady rest
Work
Steady rest is made of cast iron.
It may be made to slide on the lathe
bedways and clamped at any desired position where the workpiece needs support. It has three jaws. These jaws can
be adjusted according to the diameter of
the work. Machining is done upon the
distance starting from the headstock to
the point of support of the rest. One or
more steady rests may be used to support the free end of a long work. A
steady rest is illustrated in Fig 1.28.
Hinge
Jaw
Bed
Fig 1.28 Steady rest
28
Follower rest
It consists of a ‘C’ like casting having two adjustable jaws to support the workpiece. The
rest is bolted to the back end of the carriage. During machining, it supports the work and
moves with the carriage. So, it follows the tool to give continuous support to the work to be able
to machine along the entire length of the work.
In order to reduce friction between the work and the jaws, proper lubricant should
be used. Fig 1.29 shows a follower rest.
Jaw
Work
Carriage
Fig 1.29 Follower rest
1.7 Cutting speed, feed and depth of cut
1.7.1 Cutting speed
The cutting speed is the distance travelled by a point on the outer surface of the work
in one minute. It is expressed in meters per minute.
πdn
Cutting speed = ——— m/min.
1,000
Where
‘d’ - is the diameter of the work in mm.
‘n’ - is the r.p.m. of the work.
29
1.7.2 Feed
The feed of a cutting tool in a lathe work is the distance the tool advances for each
revolution of the work. Feed is expressed in millimeters per revolution.
1.7.3 Depth of cut
The depth of cut is the perpendicular distance measured from the machined surface
to the uncut surface of the workpiece. It is expressed in millimeters.
In a lathe, the depth of cut is expressed as follows
d1 – d2
Depth of cut = ————
2
Where
‘d1’ - diameter of the work surface before machining
‘d 2’ - diameter of the machined surface
1.8 Tools used in a lathe
Tools used in a lathe are classified as follows
A. According to the construction, the lathe tools are classified into three types
1. Solid tool
2. Brazed tipped tool
3. Tool bit and tool holders
B.According to the operation to be performed, the cutting tools are classified as
1. Turning tool
2. Thread cutting tool
3. Facing tool
4. Forming tool
5. Parting tool
6. Grooving tool
7. Boring tool
8. Internal thread cutting tool
9. Knurling tool
C. According to the direction of feed movement, the following tools are used
1. Right hand tool
2. Left hand tool
3. Round nose tool
30
Some types of lathe tools are illustrated in Fig. 1.30
Solid tool
Tipped tool
Tool holder and tool bit
Fig 1.30 Types of tools
1.9 Operations performed in a lathe
Various operations are performed in a lathe other than plain turning. They are
1. Facing
2. Turning
a. Straight turning
b. Step turning
3. Chamfering
4. Grooving
5. Forming
6. Knurling
7. Undercutting
8. Eccentric turning
9. Taper turning
10.Thread cutting
11. Drilling
12. Reaming
13. Boring
14. Tapping
31
1.9.1 Facing
Facing is the operation of machining the ends of a piece of work to produce flat
surface square with the axis. The operation involves feeding the tool perpendicular to the
axis of rotation of the work. Facing operation is illustrated in Fig. 1.31
Work
Facing tool
Direction
of feed
Fig 1.31 Facing
1.9.2 Turning
Turning in a lathe is to remove excess material from the workpiece to produce a
cylindrical surface of required shape and size. Straight turning operation is illustrated in
Fig. 1.32
Straight turning
The work is turned straight when it is made to rotate about the lathe axis and the
tool is fed parallel to the lathe axis. The straight turning produces a cylindrical surface by
removing excess metal from the workpieces.
Work
Turning tool
Fig 1.32 Straight turning
32
Step turning
Step turning is the process of turning different surfaces having different diameters.
The work is held between centres and the tool is moved parallel to the axis of the lathe. It is
also called shoulder turning.
1.9.3 Chamfering
Chamfering is the operation of bevelling the extreme end of the workpiece. The form
tool used for taper turning may be used for this purpose. Chamfering is an essential
operation after thread cutting so that the nut may pass freely on the threaded workpiece.
Chamfering is shown in Fig. 1.33
Work
Form tool
Fig 1.33 Chamfering
1.9.4 Grooving
Grooving is the process of cutting a narrow goove on the cylindrical surface of the
workpiece. It is often done at end of a thread or adjacent to a shoulder to leave a small
margin. The groove may be square, radial or bevelled in shape. Different types of grooves
are shown in Fig. 1.34
Work
Grooving tool
Fig 1.34 Grooving
1.9.5 Forming
Forming is a process of turning a convex, concave or any irregular shape. For turning
a small length formed surface, a forming tool having cutting edges conforming to the shape
required is fed straight into the work.
33
1.9.6 Knurling
Knurling is the process of embossing a diamond shaped pattern on the surface of the
workpiece. The knurling tool holder has one or two hardened steel rollers with edges of
required pattern. The tool holder is pressed against the rotating work. The rollers emboss
the required pattern. The tool holder is fed automatically to the required length.
Knurls are available in coarse, medium and fine pitches. The patterns may be
straight, inclined or diamond shaped. Fig. 1.35 shows the operation of knurling.
Work
Knurling roll
Tool holder
Fig 1.35 Knurling
The purpose of knurling is
1. to provide an effective gripping surface
2. to provide better appearance to the work
3. to slightly increase the diameter of the work
1.9.7 Undercutting
Undercutting is done
(i) at the end of a hole
(ii) near the shoulder of stepped cylindrical surfaces
(iii) at the end of the threaded portion in bolts
It is a process of enlarging the diameter if done internally and reducing the diameter
if done externally over a short length. It is useful mainly to make fits perfect. Boring tools
and parting tools are used for this operation.
Fig. 1.36 shows the operation of undercutting.
34
Work
Parting tool
Fig 1.36 Undercutting
1.9.8 Eccentric turning
If a cylindrical workpiece has two separate axes of rotating, one being out of centre
to the other, the workpiece is termed as eccentric and turning of different surfaces of the
workpiece is known as eccentric turning. Eccentric turning is shown in Fig. 1.37. The
distance between the axes is known as offset. Eccentric turning may also be done on some
special machines. If the offset distance is more, the work is held by means of special
centres. If the offset between the centres is small, two sets of centres are marked on the
faces of the work. The work is held and rotated between each set of centres to machine the
eccentric surfaces.
Offset distance
Fig 1.37 Eccentric turning
1.9.9 Taper turning
Taper
A taper may be defined as a uniform increase or decrease in diameter of a piece of
work measured along its length.
Taper turning methods
1. Form tool method
2. Compound rest method
3. Tailstock setover method
4. Taper turning attachment method
5. Combined feed method
35
(i) Form tool method
A broad nose tool is ground to the required length and angle. It is set on the work by
providing feed to the cross-slide. When the tool is fed into the work at right angles to the
lathe axis, a tapered surface is generated.
This method is limited to turn short lengths of taper only. The length of the taper is
shorter than the length of the cutting edge. Less feed is given as the entire cutting edge will
be in contact with the work.
Taper turning by form tool method is illustrated in Fig. 1. 38
Work
Form tool
Fig 1.38 Taper turning by form tool method
(ii) Compound rest method
The compound rest of the lathe is attached to a circular base graduated in degrees,
which may be swiveled and clamped at any desired angle. The angle of taper is calculated
using the formula
D-d
tan Ø = ---------2l
Where
D – Larger diameter
d – Smaller diameter
l – Length of the taper
Ø - Half taper angle
36
The compound rest is swiveled to the angle calculated as above and clamped. Feed
is given to the compund slide to generate the required taper. Taper turning by compound
rest method is illustrated in Fig. 1.39
Work
Compund rest
Fig 1.39 Taper turning by compound rest method
(iii) Tailstock setover method
Turning taper by the setover method is done by shifting the axis of rotation of the
workpiece at an angle to the lathe axis and feeding the tool parallel to the lathe axis. The
construction of tailstock is designed to have two parts namely the base and the body. The
base is fitted on the bed guideways and the body having the dead centre can be moved at
cross to shift the lathe axis.
The amount of setover - s, can be calculated as follows
D-d
s = L x -------2l
where
s - Amount of setover
D – Larger diameter
d – Smaller diameter
L - Length of the work
l – Length of the taper
The dead centre is suitably shifted from its original position to the calculated
distance. The work is held between centres and longitudinal feed is given by the carriage to
generate the taper.
37
The advantage of this method is that the taper can be turned to the entire length of
the work. Taper threads can also be cut by this method.
The amount of setover being limited, this method is suitable for turning small tapers
(approx. upto 8°). Internal tapers cannot be done by this method.
Taper turning by tailstock setover method is illustrated in Fig. 1.40
Dead centre
Live centre
Work
Fig 1.40 Taper turning by tailstock setover method
(iv) Taper attachment method
The taper attachment consists of a bracket which is attached to the rear end of the
lathe bed. It supports a guide bar pivoted at the centre. The bar having graduation in
degrees may be swiveled on either side of the zero graduation and set at the desired angle
to the lathe axis. A guide block is mounted on the guide bar and slides on it. The cross slide
is made free from its screw by removing the binder screw. The rear end of the cross slide
is tightened with the guide block by means of a bolt. When the longitudinal feed is engaged,
the tool mounted on the cross slide will follow the angular path as the guide block will slide
on the guide bar set at an angle of the lathe axis. The depth of cut is provided by the compound
slide which is set parallel to the cross-slide.
38
The advantage of this method is that long tapers can be machined. As power feed
can be employed, the work is completed at a shorter time. The disadvantage of this method
is that internal tapers cannot be machined. Taper turning by taper attachment method is
illustrated in Fig. 1. 41
Guide block
Guiding bar
Bracket
Binder screw
Fig 1.41 Taper turning by taper attachment method
(v) Combined feed method
Feed is given to the tool by the carriage and the cross-slide at the same time to move
the tool at resultant direction to turn tapers.
1.9.10 Thread cutting
Thread cutting is one of the most important operations performed in a lathe. The
process of thread cutting is to produce a helical groove on a cylindrical surface by feeding the
tool longitudinally.
1. The job is revolved between centres or by a chuck. The longitudinal feed should be
equal to the pitch of the thread to be cut per revolution of the work piece.
39
2. The carriage should be moved longitudinally obtaining feed through the leadscrew
of the lathe.
3. A definite ratio between the longitudinal feed and rotation of the headstock spindle
should be found out. Suitable gears with required number of teeth should be mounted on the
spindle and the leadscrew.
4. A proper thread cutting tool is selected according to the shape of the thread. It is
mounted on the toolpost with its cutting edge at the lathe axis and perpendicular to the axis
of the work.
5. The position of the tumbler gears are adjusted according to the type of the thread
(right hand or left hand).
6. Suitable spindle speed is selected and it is obtained through back gears.
7. Half nut lever is engaged at the right point as indicated by the thread chasing dial.
8. Depth of cut is set suitably to allow the tool to make a light cut on the work.
9. When the cut is made for the required length, the half nut lever is disengaged. The
carriage is brought back to its original position and the above procedure is repeated until the
required depth of the thread is achieved.
10. After the process of thread cutting is over, the thread is checked by suitable
gauges.
Spindle
gear
Spindle
Work
Tool
Carriage
Gear on
the
leadscrew
Leadscrew
Fig 1.42 Thread cutting
40
QUESTIONS
I.A. Choose the correct option
1. The tool used in a lathe is a
a. multipoint cutting tool
c. saw tooth cutting tool
b. single point cutting tool
d. drill
2. Lathe was first developed by
a. Henry Maudslay
b. Eli Whitney
c. James Nasmith d. Michael Faraday
3. Polishing lathe is a type of
a. engine lathe
c. high speed lathe
b. tool room lathe
d. automatic lathe
4. The spindle speed of high speed lathe is around
a. 600-1000 r.p.m
b. 1200-3200 r.p.m
c. 2000-2400 r.p.m
d. 3500-4000r.p.m
5. Turret and capstan lathes are classified under
a. automatic lathes
b. semi-automatic lathes
c. bench lathe
d. tool room lathe
6. The assembly which consists of saddle, cross-slide, compound slide and tool post is
a. headstock
b. tailstock
c. bed
d. carriage
7. Knurling tool (knurl) is a
a. single point cutting tool
c. embossing tool
b. saw tooth cutting tool
d. parting tool
8. A part useful in turning tapers is
a. cross-slide
b. compound rest c. saddle
d. apron
9. Formula for finding cutting speed in a lathe is
a. πdn
b. D - d
c. πr 2h
d. D - d
L
---------------- x ---1000
2l
2
l
10. An important operation performed in a lathe is
a. machining flat surface
b. thread cutting c. gear cutting
d. grinding
I. B. Answer the following questions in one or two words
1. Name the type of lathe used for making vessels from sheet metal.
2. Name a device useful in holding a long workpiece.
3. Mention the types of lathe bedways.
4. What is the name of the device useful in holding a work with a central hole?
41
5. Name the operation performed by offsetting the tailstock.
II Answer the following questions in one or two sentences
1. What is turning?
2. What are the important parts of a lathe?
3. Mention any four operations performed in a lathe.
4. What are the uses of a tool room lathe?
5. Mention the special feature of turret and capstan lathe?
6. What is swing diameter in a lathe?
7. What are the advantages of a V-bed?
8. Mention two types of tool post?
9. What is the use of tumbler gears?
10. What are the uses of leadscrew in a lathe?
11. What are the uses of back gears in a lathe?
12. Mention any four work holding devices used in a lathe.
13. Mention the use of a face plate.
III. Answer the following questions in about a page
1. List out the types of lathe.
2. Mention the differences between a engine lathe and a turret lathe?
3. What are the differences between a turret lathe and a capstan lathe?
4. How is the size of a lathe specified?
5. What are the parts found in the carriage of a lathe ? Explain any two.
IV. Answer the following questions in detail
1. Draw a neat sketch of a lathe and label its parts.
2. Explain the construction of tailstock of a lathe with a diagram.
3. Draw and explain the apron mechanism.
4. Explain with a diagram how different spindle speeds are obtained with a step cone
pulley drive.
5. Explain the back gear arrangement with a diagram.
6. Draw an all geared headstock and explain.
7. Explain any four work holding devices in a lathe with suitable diagrams.
42
2. DRILLING MACHINE
2.1 Introduction
Drilling machine is one of the most important machine tools in a workshop. It was
designed to produce a cylindrical hole of required diameter and depth on metal workpieces.
Though holes can be made by different machine tools in a shop, drilling machine is
designed specifically to perform the operation of drilling and similar operations. Drilling can
be done easily at a low cost in a shorter period of time in a drilling machine.
Drilling can be called as the operation of producing a cylindrical hole of required
diameter and depth by removing metal by the rotating edges of a drill.
The cutting tool known as drill is fitted into the spindle of the drilling machine. A mark
of indentation is made at the required location with a center punch. The rotating drill is
pressed at the location and is fed into the work. The hole can be made upto a required
depth.
2.2 Construction of a drilling machine
The basic parts of a drilling machine are a base, column, drillhead and spindle.
The base made of cast iron may rest on a bench, pedestal or floor depending upon the
design. Larger and heavy duty machines are grounded on the floor. The column is mounted
vertically upon the base. It is accurately machined and the table can be moved up and down
on it. The drill spindle, an electric motor and the mechanism meant for driving the spindle at
different speeds are mounted on the top of the column. Power is transmitted from the
electric motor to the spindle through a flat belt or a ‘V’ belt.
2.3 Types of drilling machines
Drilling machines are manufactured in different types and sizes according to the type
of operation, amount of feed, depth of cut, spindle speeds, method of spindle movement
and the required accuracy.
43
The different types of drilling machines are:
1. Portable drilling machine (or) Hand drilling machine
2. Sensitive drilling machine (or) Bench drilling machine
3. Upright drilling machine
4. Radial drilling machine
5. Gang drilling machine
6. Multiple spindle drilling machine
7. Deep hole drilling machine
2.3.1 Portable drilling machine
Portable drilling machine can be carried and used anywhere in the workshop. It is used
for drilling holes on workpieces in any position, which is not possible in a standard drilling
machine. The entire drilling mechanism is compact and small in size and so can be carried
anywhere. This type of machine is widely adapted for automobile built-up work. The motor
is generally universal type. These machines can accommodate drills from 12mm to 18 mm
diameter. Portable drilling machines are operated at higher speeds.
2.3.2 Sensitive drilling machine
It is designed for drilling small holes at high speeds in light jobs. High speed and hand
feed are necessary for drilling small holes. The base of the machine is mounted either on a
bench or on the floor by means of bolts and nuts. It can handle drills upto 15.5mm of
diameter. The drill is fed into the work purely by hand . The operator can sense the progress
of the drill into the work because of hand feed. The machine is named so because of this
reason. A sensitive drilling machine consists of a base, column, table, spindle, drillhead and
the driving mechanism.
A sensitive drilling machine is shown in Fig. 2.1.
Base
The base is made of cast iron and so can withstand vibrations. It may be mounted on a
bench or on the floor. It supports all the other parts of the machine on it.
Column
The column stands vertically on the base at one end. It supports the work table and the
drill head. The drill head has drill spindle and the driving motor on either side of the column.
44
‘V’ belt
Step
conepulley
Feed handle
Electric
motor
Drillhead
Sleeve
Spindle
Column
Table
Base
Fig 2.1 Sensitive drilling machine
Table
The table is mounted on the vertical column and can be adjusted up and down on it.
The table has ‘T’-slots on it for holding the workpieces or to hold any other work holding
device. The table can be adjusted vertically to accommodate workpieces of different
heights and can be clamped at the required position.
Drill head
Drillhead is mounted on the top side of the column. The drill spindle and the driving
motor are connected by means of a V-belt and cone pulleys. The motion is transmitted to
the spindle from the motor by the belt. The pinion attached to the handle meshes with the
rack on the sleeve of the spindle for providing the drill the required downfeed. There is no
power feed arrangement in this machine. The spindle rotates at a speed ranging from 50 to
2000 r.p.m.
45
2.3.3 Upright drilling machine
The upright drilling machine is designed for handling medium sized workpieces.
Though it looks like a sensitive drilling machine, it is larger and heavier than a sensitive
drilling machine. Holes of diameter upto 50mm can be made with this type of machine.
Besides, it is supplied with power feed arrangement. For drilling different types of work, the
machine is provided with a number of spindle speeds and feed.
Step
conepulley
Downfeed
handle
Electric motor
Column
Spindle
Table
Base
Fig 2.2 Upright drilling machine
46
There are two different types of upright drilling machines according to the
cross-section of the column and they are
1. Round column section upright drilling machine
2. Box column section upright drilling machine
A round column section upright drilling machine is shown in Fig. 2.2.
The main parts of a upright drilling machine are : base, column, table and drillhead.
Base
Base is made of cast iron as it can withstand vibrations set by the cutting action. It is
erected on the floor of the shop by means of bolts and nuts. It is the supporting member as
it supports column and other parts on it. The top of the base is accurately machined and has
‘T’-slots. When large workpieces are to be held, they are directly mounted on the base.
Column
Column stands vertically on the base and supports the work table and all driving
mechanisms. It is designed to withstand the vibrations set up due to the cutting action at high
speeds.
Table
Table is mounted on the column and can be adjusted up and down on it. It is provided
with ‘T’-slots for workpieces to be mounted directly on it. Table may have the following
adjustments
(i) Vertical adjustment obtained by the rack on the column and a pinion in the table
(ii) Circular adjustment about its own axis
After the required ajustments are made, the table is clamped in position.
Drill head
The drillhead is mounted on the top of the column. It houses the driving and feeding
mechanism of the spindle. The spindle can be provided with hand or power feed . There are
separate hand wheels for quick hand feed and sensitive hand feed. The handle is spring
loaded so that the drill spindle is released from the work when the operation is over.
47
2.3.4 Radial drilling machine
The radial drilling machine is intended for drilling on medium to large and heavy
workpieces. It has a heavy round column mounted on a large base. The column supports a
radial arm, which can be raised or lowered to enable the table to accommodate workpieces
of different heights. The arm, which has the drilllhead on it, can be swung around to any
position. The drill head can be made to slide on the radial arm. The machine is named so
because of this reason. It consists of parts like base, column, radial arm, drillhead and
driving mechanism. A radial drilling machine is illustrated in Fig. 2.3
Motor for
elevating screw
Guideways on the radial arm
Motor for driving the
spindle
Elevating
screw
Drillhead
Radial arm
Handle
Spindle
Cloumn
Table
Base
Fig 2.3 Radial drilling machine
Base
The base is a large rectangular casting and is mounted on the floor of the shop. Its top
is accurately finished to support a column at one end and the table at the other end. ‘T’-slots
are provided on it for clamping workpieces.
48
Column
The column is a cylindrical casting, which is mounted vertically at one end of the base.
It supports the radial arm and allows it to slide up and down on its face. The vertical
adjustment of the radial arm is effected by rotating a screw passing through a nut attached
to the arm. An electric motor is mounted on the top of the column for rotating the elevating
screw.
Radial arm
The radial arm is mounted on the column parallel to the base and can be adjusted
vertically. The vertical front surface is accurately machined to provide guideways for the
drillhead. The drillhead can be adjusted along these guideways according to the location of
the work. In some machines, a separate motor is provided for this movement. The arm may
be swung around the column. It can also be moved up and down to suit workpieces of
different heights.
Drillhead
The drillhead is mounted on the radial arm and houses all mechanism for driving the
drill at different speeds and at different feed. A motor is mounted on top of the drillhead for
this purpose. To adjust the position of drill spindle with respect to the work, the drillhead
may be made to slide on the guideways of the arm. The drillhead can be clamped in position
after the spindle is properly adjusted.
Universal radial drilling machine
It is a machine in which the spindle can be swiveled to any required angle in vertical
and horizontal positions.
2.3.5. Gang drilling machine
Gang drilling machine has a long common table and a base. Four to six drillheads are
placed side by side. The drillheads have separate driving motors. This machine is used for
production work.
A series of operations like drilling, reaming, counterboring and tapping may be
performed on the work by simply shifting the work from one position to the other on the
work table. Each spindle is set with different tools for different operations.
Fig.2.4 shows a gang drilling machine.
49
Drillhead
Feed handle
Column
Spindle
Handle
for
elevating
the table
Table
Elevating
screw
Base
Fig 2.4 Gang drilling machine
2.3.6 Multiple spindle drilling machine
This machine is used for drilling a number of holes in a workpiece simultaneously and
for reproducing the same pattern of holes in a number of identical pieces. A multiple spindle
drilling machine also has several spindles. A single motor using a set of gears drives all the
spindles. All the spindles holding the drills are fed into the work at the same time. The
distances between the spindles can be altered according to the locations where holes are to
be drilled. Drill jigs are used to guide the drills.
2.3.7 Deep hole drilling machine
A special machine and drills are required to drill deeper holes in barrels of gun,
spindles and connecting rods. The machine designed for this purpose is known as deep hole
drilling machine. High cutting speeds and less feed are necessary to drill deep holes. A nonrotating drill is fed slowly into the rotating work at high speeds. Coolant should be used
while drilling in this machine. There are two different types of deep hole drilling machines
1. Vertical type
2. Horizontal type
2.4 Size of a drilling machine
Drilling machines are specified according to their type.
A portable drilling machine is specified by the maximum diameter of the drill that it can
handle.
50
The size of the sensitive and upright drilling machines are specified by the size of the
largest workpiece that can be centered under the spindle. It is slightly smaller than twice the
distance between the face of the column and the axis of the spindle.
Particulars such as maximum size of the drill that the machine can operate, diameter of
the table, maximum travel of the spindle, numbers and range of spindle speeds and feeds
available, morse taper number of the drill spindle, floor space required, weight of the
machine, power input are also needed to specify the machine completely. The size of the
radial drilling machine is specified by the diameter of the column and length of the radical
arm.
2.5 Drill spindle assembly
A drill spindle assembly is illustrated in Fig. 2.5. The drill spindle is a vertical shaft,
which holds the drill. A long keyway is cut on the spindle and a sliding key connects it with
a bevel gear or a stepped cone pulley. It receives motion from the driving motor. The spindle
rotates within a non-rotating sleeve known as quill. The spindle and the sleeve are
connected by a thrust bearing.
Keyway on the spindle
Spindle
Nut
Thrust bearing
Rack
Pinion
Sleeve
Thrust bearing
Washer
Lower end of the spindle
Fig 2.5 Drill spindle
51
Rack teeth are cut on the outer surface of the quill. The sleeve (quill) may be moved up
and down by rotating a pinion which meshes with the rack. This movement is given to the
spindle for providing the required feed. As there is a long keyway on top of the spindle, it is
connected to the driving mechanism even during the feed movement.
A morse taper hole is provided at the lower end of the spindle. It is useful in
accommodating a taper shank drill. The tang of the drill fits into a slot provided at the end of
the taper hole. To remove the drill from the spindle a drift may be pushed through the slot.
The spindle drive is obtained in three methods. They are:
1. Step cone pulley drive
2. Step cone pulley with back gear arrangement
3. Gear box drive
2.6 Work holding devices
The work should be held firmly on the machine table before performing any operation
on it. As the drill exerts very high quantity of torque while rotating, the work should not be
held by hand. If the workpiece is not held by a proper holding device, it will start rotating
along with the tool causing injuries to the operator and damage to the machine.
The devices used for holding the work in a drilling machine are
1. Drill vise
2. ‘T’ - bolts and clamps
3. Step block
4. V - block
5. Angle plate
6. Drill jigs
2.6.1 Drill vise
Vise is one of the important devices used for holding workpices on a drilling machine
table. The work is clamped in a vise between a fixed jaw and a movable jaw.
Parallel blocks are placed below the work so that the drill may completely pass
through the work without damaging the table. Different types of vises are used for holding
different types of work and for performing different operations.
52
The different types of vises are
1. Plain vise
2. Swivel vise
3. Tilting vise
4. Universal vise
A plain vise is shown in Fig. 2.6.
Movable jaw
Screw
Fixed jaw
Work
Fig 2.6 Drill vice
2.6.2 ‘T’ - bolts and clamps
The workpieces can be held directly on the machine table by means of ‘T’ - bolts and
clamps. The top of the machine table has ‘T’ - slots into which ‘T’ - bolts may be fitted. The
bolts of diameter 15 to 20mm are used. The clamps are made of mild steel. ‘T’ - bolts pass
through a central hole on the clamp. The clamp is made to rest horizontally on the work
surface by placing a suitable step block at the other end of the work.
Some of the common types of clamps are: Plain slot clamp, goose-neck clamp and
finger clamp. Fig. 2.7 illustrates ‘T’ - bolt and a clamp.
‘T’ bolt
Clamp
Step block
Work
Fig 2.7
‘T’ bolt & clamp
53
2.6.3 Step blocks
The step blocks are used in
combination with ‘T’ - bolts and clamps
for holding the work directly on the
table. The step block supports the
other end of the clamp. Workpieces of
different heights are held by leveling the
clamp on different steps of the step
block. Fig. 2.8 illustrates a step
block.
Fig 2.8 Step block
2.6.4 ‘V’ - block
‘V’ - blocks are used for holding cylindrical workpieces. The work may be supported
on two or three ‘V’ - blocks according to the length of the work. The work is held on the
‘V’ groove and is clamped by straps and bolts. They are made of cast iron or steel and are
accurately machined. Fig. 2.9 shows the use of a ‘V’ - block.
Screw
‘U’ clamp
Work
‘V’ block
Fig 2.9 ‘V’ block
2.6.5 Angle plate
Angle plates have two faces at right angle to each other and are made of cast iron.
It resembles the English alphabet ‘L’. All the sides of a angle plate are machined accurately.
Slots and holes are provided on both the faces of the angle plate. Work is clamped on one
of its faces by means of bolts and nuts. The use of an angle plate is shown in Fig. 2.10
54
Work
Angle plate
Fig 2.10 Angle plate
2.6.6 Drill Jig
Drill jigs are used in mass production process. A jig is specially designed to hold the
work securely and to guide the tool at any desired position. Holes may be drilled at the
same relative positions on each of the identical workpieces.
The work is clamped and removed easily. The cost of making a drill jig is more but a
low order of skill is sufficient to work with a drill jig. Fig 2.11 illustrates a drill jig.
Different types of drill jigs are
1. Plate jig
4. Box jig
2. Channel jig
5. Indexing jig.
3. Diameter jig
Drill
‘T’ bolt
Drill bush
Jig
Work
Table
Fig 2.11 Drill jig
55
2.7 Tools used in a drilling machine
Different tools are used for performing different types of operations. The most
commonly used tools in a drilling machine are
1. Drill
2. Reamer
3. Counterbore
4. Countersink
5. Tap
2.7.1 Drill
A drill is a tool used to originate a hole in a solid material. A helical groove known as
‘flute’ is cut along the length of the drill.
Different types of drills are
1. Flat Drill
2. Straight fluted drill
3. Twist drill
4. Centre drill
Twist drills are the type generally used in shop work. They are made of High speed
steel (HSS) or High carbon steel.
There are two types of twist drills namely (i) Straight shank twist drill and (ii) Taper
shank twist drill. The diameter of the straight shank drill ranges from 2 to 16mm. Taper
shanks are provided on drills of larger diameter.
2.7.2 Reamer
The tool used for enlarging and finishing a previously drilled hole is known as a reamer.
It is a multi tooth cutter and removes smaller amount of material. It gives a better fnish and
accurate dimension.
2.7.3 Counterbore
A Counterbore is a multi tooth cutting tool used for enlarging the top of the previously
machined hole. It has three or four cutting teeth.
The flutes on them may be straight or helical. Straight fluted tools are used for
machining softer materials like brass and aluminium and for short depth of cut. Helical fluted
counterbores are used for longer holes.
56
2.7.4 Countersink
A countersink has cutting edges on its conical surfaces. It has a similar construction of
a counterbore except for the angle of the cutting edges.The angle of countersinks will
generally be 60°, 82° or 90°. It is used for enlarging the top of the holes conically.
2.7.5 Tap
A tap has threads like a bolt.It has three to four flutes cut across the threads. It can cut
threads on the inside of a hole. The flutes on the threads form the cutting edges. It is a multi
point cutting tool. It will dig into the walls of the hole as the lower part of the tap is slightly
tapered. The shank of the tap is square shaped to enable it to be held by a tap wrench.
2.7.6 Twist drill nomenclature
Axis
It is the longitudinal centerline of the drill running through the centres of the tang and
the chisel edge.
Body
It is the part of the drill from its extreme point to the commencement of the neck, if
present. Otherwise, it is the part extending upto the commencement of the shank. Helical
grooves are cut on the body of the drill.
Shank
It is the part of the drill by which it is held and driven. It is found just above the body
of the drill. The shank may be straight or taper. The shank of the drill can be fitted directly
into the spindle or by a tool holding device.
Tang
The flattened end of the taper shank is known as tang. It is meant to fit into a slot in
the spindle or socket. It ensures a positive drive of the drill.
Neck
It is the part of the drill, which is diametrically undercut between the body and the
shank of the drill. The size of the drill is marked on the neck.
Point
It is the sharpened end of the drill. It is shaped to produce lips, faces, flanks and chisel edge.
57
Lip
It is the edge formed by the intersection of flank and face. There are two lips and both
of them should be of equal length. Both lips should be at the same angle of inclination with
the axis (59°).
Flute length
Neck
Tang
Flute
Land
Flank
Body
Shank
Overall length
Lip clearance angle
Land
Rake angle
Flank
Chisel
edge
angle
Face
Chisel edge
Lip
Point angle
Fig 2.12 Twist drill nomenclature
Land
It is the cylindrically ground surface on the leading edges of the drill flutes adjacent to
the body clearance surface. The alignment of the drill is maintained by the land. The hole is
maintained straight and to the right size.
58
Flutes
The grooves in the body of the drill are known as flutes. Flutes form the cutting edges
on the point. It allows the chips to escape and make them curl. It permits the cutting fluid to
reach the cutting edges.
Angles
Chisel edge angle
The obtuse angle included between the chisel edge and the lip as viewed from the end
of the drill. It usually ranges from 120° to 135°.
Helix angle or rake angle
The helix or rake angle is the angle formed by the leading edge of the land with a plane
having the axis of the drill. If the flute is straight, parallel to the drill axis, then there would be
no rake. If the flute is right handed, then it is positive rake and the rake is negative if it is left
handed. The usual value of rake angle is 30° or 45°.
Point angle
This is the angle included between the two lips projected upon a plane parallel to the
drill axis and parallel to the two cutting lips. The usual point angle is 118°. When hard alloys
are drilled the value increases.
Lip clearance angle
The angle formed by the flank and a plane at right angles to the drill axis. The angle is
normally measured at the periphery of the drill. The lip clearance angle ranges from 12° to 15°.
2.8 Tool holding devices
Different tools are used for performing different operations. They are fitted into the
drill spindle by different methods. They are
1. By directly fitting in the spindle
2. By a sleeve
3. By a socket
4. By a chuck
5. Tapping attachment
59
2.8.1 Spindle
Almost all drilling machines have their spindle bored out to a standard taper(1:20) to
receive the taper shank of the tool. While fitting the tool, the shank of the drill (or any other
tool) is forced into the tapered hole and the tool is gripped by friction. The tool may be
rotated with the spindle by friction between the tapered surface and the spindle. But to
ensure a positive drive, the tang of the tool fits into a slot at the end of the taper hole. The
tool may be removed by pressing a tapered wedge known as drift into the slotted hole of the
spindle.
2.8.2 Sleeve
The drill spindle is suitable for holding only one size of tool shank. If the shank of the
tool is smaller than the taper in the spindle hole, a taper sleeve is used. The outside taper of
the sleeve conforms to the spindle taper and the inside taper holds the shanks of the smaller
size tools. The sleeve has a flattened end or tang which fits into the slot of the spindle. The
tang of the tool fits into a slot provided at the end of the taper hole of the sleeve. Different
sizes of tool shanks may be held by using different sizes of sleeve. In order to remove the
drill from the spindle, the drill along with the sleeve is removed with the help of a drift. The
drill is then removed from the sleeve by the same method.
Fig. 2.13 illustrates a sleeve.
Tang
Tang
Taper shank
Slot
Taper body
Slot
Body
Fig 2.13 Drill sleeve
Fig 2.14 Drill socket
60
2.8.3 Socket
Drill sockets are much longer in size than the drill sleeves. A socket consists of a solid
shank attached to the end of a cylindrical body. The taper shank of the socket conforms to
the taper of the drill spindle and fits into it. The body of the socket has a tapered hole larger
than the drill spindle taper into which the taper shank of any tool may be fitted. The tang of
the socket fits into slot of the spindle and the tang of the tool fits slot of the socket.
Fig. 2.14 illustrates a socket.
2.8.4 Drill chuck
This type of chuck is particularly adapted for holding tools having straight shanks. The
drill chuck has a taper shank which fits into the taper hole of the spindle. The jaws fitted in
the body of the chuck holds the straight shank drills. Fig. 2.15 illustrates a drill chuck.
Shank
Nut
Sleeve
Key
Spring
Body
Clutch plates
Jaws
Fig 2.16
Tapping attachment
Fig 2.15 Drill chuck
2.8.5. Tapping attachment
The tapping attachment is used to hold the tool known as ‘tap’. It serves as a flexible
connection between the spindle and the tap. The taper shank of the attachment is fitted into
the drill spindle. The tap is fitted at the bottom of the attachment. The tap is fed into the
specific hole by the spindle, rotating it in clockwise direction. After the threads are cut, the
spindle is released from the hole. The bottom of the attachment rotates in anti-clockwise
direction causing no damage to the tapped hole. Tapping attachments are used during
production work. Fig. 2.16 illustrates a tapping attachment.
61
2.9 Drilling machine operations
Though drilling is the primary operation performed in a drilling machine, a number of
similar operations are also performed on holes using different tools.The different operations
that can be performed in a drilling machine are:
1. Drilling
2. Reaming
3. Boring
4. Counterboring
5. Countersinking
6. Spot facing
7. Tapping
8. Trepanning
2.9.1 Drilling
Drilling is the operation of producing a cylindrical hole of required diameter and depth
by removing metal by the rotating edge of a cutting tool called drill. Drilling is one of the
simplest methods of producing a hole. Drilling does not produce an accurate hole in a
workpiece. The internal surface of the hole generated by drilling becomes rough and the
hole is always slightly oversize due to vibration of the spindle and the drill. A hole made by
a drill of size 12mm will measure approximately upto 12.125mm and by a drill of size 22mm
will measure upto 22.5mm. Fig. 2.17 illustrates drilling operation.
Drill
Work
Fig 2.17 Drilling
62
2.9.2 Reaming
The size of hole made by drilling may not be accurate and the internal surface will not
be smooth. Reaming is an accurate way of sizing and finishing a hole which has been
previously drilled by a multi point cutting tool known as reamer.The surface obtained by
reaming will be smoother and the size accurate. The speed of the spindle is made half that
of drilling. Reaming removes very small amount of metal ( approx 0.375 mm). In order to
finish a hole and bring it to the accurate size, the hole is drilled slightly undersize. F i g .
2.18 illustrates reaming operation.
Reamer
Work
Fig 2.18 Reaming
2.9.3 Boring
Boring is the operation enlarging the diameter of the previously made hole. It is done
for the following reasons.
1. To enlarge a hole by means of an adjustable cutting tool. This is done when a
suitable sized drill is not available or the hole diameter is so large that is cannot be ordinarily
drilled.
2. To finish a hole accurately and bring it to the required size
3. To machine the internal surface of the hole already produced in casting
4. To correct out of roundness of the hole
5. To correct the location of the hole as the boring tool follows independent path with
respect to the hole
63
Boring tool is a tool with only one cutting edge. The tool is held in a boring bar which
has a taper shank to fit into the spindle or a socket. For perfectly finishing a hole, the job is
drilled undersize slightly. Boring operation in some precise drilling machine is performed to
enlarge the holes to an accuracy of 0.00125mm. The spindle speed during boring should be
adjusted to be lesser than that of reaming. Fig. 2.19 illustrates boring operation.
Boring bar
Work
Single point
cutting tool
Fig 2.19 Boring
2.9.4 Counterboring
Counterboring is the operation
of enlarging the end of the hole
cylindrically. The enlarged hole forms
a square shoulder with the original
hole. This is necessary in some cases
to accommodate the heads of bolts,
studs and pins. The tool used for
counter boring is known as counter
bore.
Counterbore
The counterbores are made with
cutting edges which may be straight or
spiral. The cutting speed for
counterboring is atleast 25% lesser
than that of drilling.
Fig 2.20 Counterboring
64
Work
2.9.5 Countersinking
Countersinking is the operation of making a cone shaped enlargement at the end of the
hole. The included angle of the conical surface may be in the range of 60° to 90°. It is used
to provide recess for a flat headed screw or a counter sunk rivet fitted into the hole. The tool
used for counter sinking is known as a countersink. It has multiple cutting edges on its
conical surface. The cutting speed for countersinking is 25% lesser than that of drilling.
Fig.2.21 illustrates countersinking operation.
Countersink
Work
Fig 2.21 Countersinking
2.9.6 Spot facing
Spot facing is the operation
of smoothing and squaring the
surface around a hole. It is done
to provide proper seating for a nut
or the head of a screw. A
counterbore or a special spot
facing tool may be employed for
this purpose.
Spotfacing
tool
Work
Fig. 2.22 illustrates spot
facing operation.
Fig 2.22 Spotfacing
65
2.9.7 Tapping
Tapping is the operation of cutting internal threads by means of a cutting tool called
‘tap’. Tapping in a drilling machine may be performed by hand or by power. When the tap
is screwed into the hole, it removes metal and cuts internal threads which will fit into external
threads of the same size. Fig. 2.23 illustrates tapping operation.
Work
Tap
Fig 2.23 Tapping
2.9.8 Trepanning
Trepanning is the operation of
producing a hole in sheet metal by
removing metal along the circumference
of a hollow cutting tool. Trepanning
operation is performed for producing
large holes. Fewer chips are removed
and much of the material is saved while
the hole is produced. The tool may be
operated at higher speeds. The speed
depends upon the diameter of the hole
to be made. The tool resembles a
hollow tube having cutting edges at one
end and a solid shank at the other to fit
into the drill spindle.
Tool
Work
Fig 2.24 Trepanning
66
2.10 Cutting speed, Feed & Depth of cut
2.10.1 Cutting speed
Speed in general refers to the distance a point travels in a particular period of time.
The cutting speed in a drilling operation refers to the peripheral speed of a point on the
cutting edge of the drill. It is usually expressed in meters per minute. The cutting speed (v)
may be calculated as
Cutting speed(C.S) =
π dn
----- m per min
1000
Where
‘d’ - is the diameter of the drill in mm, and
‘n’ - is the speed of the drill spindle in r.p.m.
The cutting speed of a drill depends, as in other machining processes, upon several
factors like the cutting tool material, the kind of material being drilled, the quality of surface
finish desired, the method of holding the work, the size, type and rigidity of the machine.
Example
A drill of diameter 20mm makes a hole on a steel part at a cutting speed of 25m/
min. Find out the spindle speed.
Cutting speed(C.S) =
25 =
π dn
----m per min
1000
π x 20 x n
------------1000
or n =
25 x 1000
--------------π x 20
Spindle speed,n = 398 r.p.m
2.10.2 Feed
The feed of a drill is the distance the drill moves into the work at each revolution of the
spindle. It is expressed in millimeters. The feed may also be expressed as feed per minute.
The feed per minute may be defined as the axial distance moved by the drill into the work
per minute. Feed depends upon factors like the material to be drilled, the rigidity of the
machine, power, depth of the hole and the type of finish required.
2.10.3 Depth of cut
The depth of cut in drilling is equal to one half of the drill diameter. If ‘d’ is the
diameter of the drill, the depth of cut (t) t = d/2 mm.
67
2.11 Safety precautions
It is necessary that no damage is done to the operator, the machine tool and the cutting
tool. To ensure this, the following points are to be remembered.
1. The work should not be held by hand in any case.
2. Proper work holding device should be used to hold the work. If the work is not
held properly, the work tends to rotate along with the drill causing damage to the
operator, the machine tool and the cutting tool.
3. The shank of the drill should be cleaned before it is fitted into the spindle. The dirt
on the shank may make the drill not to have a proper fit into the spindle. This will
lead to breakage of drill.
4. The taper hole of the spindle should also be cleaned.
5. The shank of the drill should conform with the spindle hole.
6. Cutting speed and feed should be selected according to the prescribed range.
7. Care should be taken to ensure whether the belt and gears are connected properly.
8. Proper safety plates should be installed around rotating parts like belt drive and
gears.
9. The operator should wear safety goggles while operating the drilling machine.
10. The machine should be disconnected from electric terminals when repairs are
undertaken. In general, we should ensure the proper functioning of the machine
tool.
QUESTIONS
I. A Choose the correct option
1. The drilling machine used in constructional work is
a. bench drilling machine
b. portable drilling machine
c. gang drilling machine
d. multiple spindle drilling machine
2. Reamer is a
a. multi point cutting tool
b. single point cutting tool
c. parting tool
d. saw teeth cutting tool
68
3. The lip clearance angle of a drill is
a. 59°
b. 118°
c. 12° to 15°
d. 180°
4. The point angle of a drill is
a. 59°
b. 118°
c. 12° to 15°
d. 180°
5. The number of revolutions of a spindle in one minute is known as
a. meters/min
b. RPM
c. TPI
d. mm/stroke
I. B Answer the following questions in one or two words
1. Name the device used to guide the tool when drillling is performed on many numbers of identical workpieces.
2. Name the groove present on the drill.
3. What is the name of the device used in holding drills with straight shanks?
4. Name the device useful in holding a cylindrical workpiece on drilling machine table.
5. What type of a drilling machine is used to drill in the barrels of guns?
II. Answer the following questions in one or two sentences
1. State any two differences between the processes of reaming and boring.
2. Why is spotfacing done?
3. Define ‘cutting speed’ in a drilling machine.
4. Name any four work holding devices used in a drilling machine.
III. Answer the following questions in about a page
1. List out the types drilling machines.
2. Draw and explain a bench drilling machine.
3. How is the size of a drilling machine specified?
4. Explain any two drill holding devices.
IV. Answer the following questions in detail
1. Draw a neat diagram of a upright drilling machine and explain.
2. Explain the working of a drill spindle with a diagram.
3. Explain the construction of a radial drilling machine.
4. Explain any four work holding devices used in a drilling machine.
5. Explain the nomenclature of a twist drill with a diagram.
6. Explain any four operations performed in a drilling machine.
69
3. SHAPING MACHINE
3.1 Introduction
Shaping is a process of machining a flat surface which may be horizontal, vertical ,
inclined, concave or convex using a reciprocating single point tool. A shaping machine is a
reciprocating type of machine tool. James Nasmith, an Englishman designed a shaping
machine to produce flat surfaces in the year 1836.
Ram
Work
Tool
Table
Fig 3.1 Shaping operation
70
3.2 Method of machining
The work is held firmly on the table and the ram is allowed to reciprocate over it. A
single point cutting tool is attached to the ram. When the ram moves horizontally in the
forward direction, the tool removes metal from the work. On the return stroke, metal is not
removed. The ram moves at a slow speed during forward stroke. But during return stroke,
the ram moves at a faster speed. Though the distances of ram movement during the forward
and return stroke remain the same, the time taken by the return stroke is less as it is faster.
It is possible by ‘Quick return mechanism’.
In a shaping machine, a flat horizontal surface is machined by moving the work
mounted on the table in a cross direction to the tool movement. When vertical surfaces are
machined, the feed is given to the tool.
When a inclined surface is machined, the vertical slide of the toolhead is swiveled to
the required angle and the feed is given to the tool by rotating the downfeed hand wheel.
The method of machining in a shaper is illustrated in Fig 3.1
3.3 Main parts of a shaping machine
Base
The base is hollow and is made of cast iron. It provides the necessary support for all
the other parts of the machine. It is rigidly bolted to the floor of the workshop.
Column
It is a box like casting mounted vertically on top of the base. Two accurate
guideways are machined on the top of the column. The ram reciprocates on these
guideways. The front face of the column is provided with two vertical guideways. They act
as guideways for the crossrail. Crossrail moves vertically along these guideways. The
column encloses the ram reciprocating mechanism and the mechanism for strokelength
adjustment.
Crossrail
It is mounted on the front vertical guideways of the column. The table may be raised
or lowered by adjusting the crossrail vertically. A horizontal cross feed screw is fitted within
the crossrail.
The construction of a shaping machine is shown in Fig. 3.2
71
Table
It is an impotant part useful in holding the work firmly on it. It is mounted on the
saddle which is located above the crossrail. The top and sides of the table are accurately
machined and have T-slots. Workpieces are held on the table with the help of shaper vise,
clamps and straps.
Ram
Ram supports the toolhead on its front. It reciprocates on the accurately machined
guideways on the top of the column. It is connected to the reciprocating mechanism placed
inside the column. The position of ram reciprocation may be adjusted according to the
location of the work on the table.
Toolhead
The toolhead is fitted on the face of the ram and holds the tool rigidly. It provides
vertical and angular feed movement of the tool. The swivel toolhead can be positioned at
any required angle and the vertical slide can be moved vertically or at any desired angle to
machine verical or inclined surfaces.
Toolhead
Ram
Tool
Table
Column
Table
support
Elevating
screw
Base
Fig 3.2 Shaping machine
72
3.4 Types of shaping machine
The shaping machines are classified as follows :
A. According to the type of driving mechanism
1. Crank type
2. Hydraulic type
3. Geared type
B. According to the design of the table
1. Plain shaper
2. Heavy duty shaper
3. Standard shaper
4. Universal shaper
C. According to the position and travel of ram
1. Horizontal shaper
2. Vertical shaper
D. According to the type of cutting stroke
1. Push cut shaper
2. Draw cut shaper
3.4.1 Crank type shaper
Crank and slotted link mechanism of a crank type shaper converts the rotation of an
electric motor into reciprocating movement of the ram. Though the lengths of both the
forward and return strokes are equal, the ram travels at a faster speed during return stroke.
This quick return is incorporated in almost all types of shaper.
3.4.2 Hydraulic shaper
The ram of a hydraulic shaper is connected to a piston. Oil at high pressure is pumped
to the cylinder of the hydraulic system. As the oil pushes the the piston, the ram
reciprocates. Hydraulic shapers are high power machines and are used for heavy duty work.
3.4.3 Universal shaper
The universal shaper has a special type of table which can be swiveled and
positioned at any angle about a horizontal axis. Apart from the cross and vertical travel, the
table of a universal shaper can be swiveled to any angle to machine inclined surfaces. In the
process, the position of the work in the table need not be changed. These machines are
utilised in precision workshops.
73
3.5 Quick return mechanism
The ram moves at a comparatively slower speed during the forward cutting stroke.
During the return stroke, the mechanism is so designed to make the tool move at a faster
rate to reduce the idle return time. This mechanism is known as quick return mechanism.
As the ram moves at a faster rate during return stroke, the time taken becomes less.
The total machining time decreases and the rate of production increases. The following
mechanisms are used for quick return of the ram.
1. Crank and slotted link mechanism
2. Hydraulic mechanism
3. Whitworth mechanism
3.5.1 Crank and slotted link mechanism
An electrical motor runs the driving pinion(S) at a uniform speed. This pinion makes
the bull gear(M) to rotate at a uniform speed. Bull gear is a large gear fitted inside the
column. The point ‘O’ is the centre of the bull gear. A slotted link having a long slot along its
length is pivoted about the point ‘K’. A sliding block ‘N’ is fitted inside the slot and slides
along the length of the slotted link. ‘P’ is the crank pin and ‘OP’ can be considered as a
crank. Fig. 3.3 shows the crank & slotted link mechanism.
When the bull gear rotates, the sliding block also rotates in the crank pin circle. This
arrangement provides a rocking movement to the rocker arm. As the top of the slotted link
is connected to the ram, the ram reciprocates horizontally. So, bull gear rotation is
converted into the reciprocating movement of the ram.
Quick return mechanism
As shown in the diagram, ‘KA’ indicates the starting point of the forward cutting stroke
and ‘KB’ the end of the cutting stroke. The rotation of the crank ‘OP’ in clockwise direction
through the angle P1RP2 refers to the forward cutting stroke. The rotation of the crank in the
same direction through the angle P 2LP 1 refers to the return stroke. As the angle P 2LP 1 is
smaller than the angle P1RP2, the time taken for the return stroke is less than that of forward
stroke. So, it is evident that the speed at which the ram travels during return stroke is more.
Time taken for forward cutting stroke
-------------------------------------------Time taken for the idle return stroke
angle P 1RP 2
= --------------angle P 2LP 1
In some machines this ratio can be set as 7/5.
74
=
216°
3
------- = -----144°
2
Clamping lever
Ram
Handwheel for
position of stroke
adjustment
Crank
Slotted link
Bevel gear
Crank pin (P)
Driving
pinion (S)
Sliding block
Bull gear
Fig 3.3 Crank and slotted link mechanism
Crank
pin
circle
The strokelength of a ram is the
distance the ram moves forward or
backward. It depends upon the distance
between the centre of the bull gear and the
centre of the sliding block. it is adjusted
according to the length of the work.
F i g . 3 . 4 i l l u s t r a t e s q u i c k re t u r n
mechanism.
Fig 3.4 Quick return mechanism of the ram
75
3.6 The size of a shaper
The size of a shaper is determined by the maximum length of stroke it can make.
Shapers with maximum strokelength of 175mm to 900mm are available. Machines with
maximum strokelength of 300mm, 450mm and 600mm are used widely.
To specify the machine further, the following points are to be provided.
1. The type of drive
a. Individual motor
b. Belt driven
2. The method of obtaining different speeds
a. Gear box
b. Step cone pulley
3. Horse power of the motor
4. Cutting to return stroke ratio
5. Number and range of speed arrangement
6. The type of the table
3.7 Strokelength calculation and adjustment
The length of the stroke is calculated to be nearly 30mm longer than the work. The
position of stroke is so adjusted that the tool starts to move from a distance of 25mm before
the beginning of the cut and continues to move 5mm after the end of the cut. For example as
shown in Fig. 3.5, the length of the work is 100mm. The strokelength of the ram is
calculated to be 130mm. (25+100+5). Fig. 3.5 illustrates the calculation of strokelength.
Toolhead
Forward stroke
Return stroke
Tool
Strokelength
25
Length of the work - 100
5
Work
Table
Fig 3.5
Strokelength calculation
76
Adjusting the strokelength
The crank pin fastened to the sliding block can be adjusted by a lever placed outside
the column. Through the bevel gears placed at the centre of the bull gear, the radial slide
lead screw can be rotated. This rotation of leadscrew changes the position of the sliding
block to move towards or away from the bull gear centre. The strokelength of the ram is
adjusted by placing the sliding block at a required position from the centre of the bull gear.
Note : The strokelength of the ram and its position should not be adjusted when the
machine is in operation. The machine should be stopped before these adjustments are made.
3.8 Method of table movement
1. The table moves in a cross direction when the crossfeed screw is rotated.
2. A crank handle is provided to rotate the the crossfeed screw manually.
3. When the crossfeed screw is rotated in clockwise direction, the table will move
towards left.
4. When the elevating screw is rotated, the table slides up and down on the face of
the column.
5. As the handles meant for crossfeed screw rotation and elevating screw rotation
are placed side by side, it is not possible to operate both of them at the same time.
6. The work mounted on the table is provided with required feed only during the end
of the return stroke.
3.8.1 Ratchet and Pawl mechanism (Automatic feed mechanism for
the table)
The table of a shaping machine travels in a cross direction when the crossfeed screw
is rotated. The cross feed screw is attached to the ratchet wheel. A spring loaded ‘pawl’ is
positioned to be placed between the teeth of the ratchet wheel. The pawl is housed within a
frame known as rocker arm. The bull gear placed inside the column of the shaping machine
drives the gear B through the gear A.
There is a diametric slot provided on the face of the gear B. A crank pin is attached
to a slider placed in the slot. The bottom of the rocker arm and the crank pin are connected
by a connecting rod. The rotation of the gear B makes the crank pin to rotate. This
movement makes the rocker arm to rock about the centre of the ratchet wheel. The pawl
makes the ratchet to rotate by a small amount in one direction only. As the cross feed screw
is attached to the ratchet wheel, the rotation of the ratchet wheel will make the table to move
in a cross direction.
77
If the direction of the table feed is to be reversed, the pawl is turned about 180°
from its position. The ratchet wheel and the crossfeed screw will rotate in the opposite
direction resulting in the table movement in the opposite direction.
Ratchet & pawl mechanism is shown in Fig. 3.6.
Knob
Spring
Pawl
Ratchet
wheel
Crank pin
Cross feed
screw
Connecting rod
Rocker arm
Fig 3.6 Ratchet and Pawl mechanism
When power feed is not necessary for the table, the pawl is disengaged from the
ratchet wheel.
3.9 Swivel toolhead
The toolhead of a shaper holds the cutting tool rigidly. It is fitted on the face of the
ram. The vertical slide of the toolhead can be moved vertically or at a particular angle to
provide vertical and angular feed movement to the tool. It allows the tool to have an automatic relief during the return stroke of the ram.
The toolhead has a swivel base attached to the circular seat on the ram. The swivel
base has angular graduations marked on it. As the vertical slide is mounted on the swivel
base of the toolhead, it may be set and moved at any desired angle to machine angular
surfaces like ‘V’ grooves and dove tail grooves.
78
The downfeed screw handle is rotated to move the vertical slide up and down. A
graduated dial is placed on the top of down feed screw to control the amount of depth of cut
or feed accurately.
Apron consisting of clapper box, clapper block and tool post is clamped on the
vertical slide by a screw. By releasing the clamping screw, the apron can be swiveled either
towards left or towards right with respect to the vertical slide. The clapper box has two
vertical walls within which the clapper block is housed. It is connected to the clapper box
with the help of a hinge pin. This arrangement provides relief to the tool while machining
vertical or angular surfaces. The tool post is mounted upon the clapper block. The tool post
is provided with a slot to accommodate the tool and a screw to hold the tool rigidly on the
tool post.
The clapper block fits securely inside the clapper box to provide a rigid tool support
during forward stroke. On the return stroke, a slight frictional drag of the tool on the work
lifts the block out of the clapper box and prevents the tool cutting edge from dragging on
the work surface. Fig. 3.7 illustrates the swivel toolhead of a shaper.
Down feed handle
Micrometer dial
Angular graduations
Down feed screw
Clapper box
Tool post
Clapper block
Tool
Fig 3.7 Swivel toolhead
79
3.10 Work holding devices
Workpieces can be held and supported on the shaper table directly or by having
some special devices. Depending on the size and shape of the work, it may be supported on
the table by any one of the following methods.
1. Shaper vise
4. Angle plate
2. Clamps and stop pins
5. V – Block
3. T-bolts and step blocks
6. Special fixtures
3.10.1 Vise
Vise is the most common and simple work holding device used in a shaper. Different
types of vises are used in a shaping machine according to the need and they are :
1. Plain vise
2. Swivel vise
3. Universal vise
Movable jaw
Fixed jaw
Screw
Swivel base
Fig 3.8 Shaper vice
3.10.2 Clamps and stop pins
T – bolts are fitted into the T - slots of the table. The work is placed on the table
The work is supported by a rectangular strip at one end and by a stop pin at the other side.
The screw is tightened to secure the work properly on the machine table. The use of stop
pin is shown in Fig. 3.9.
Stop pin
Bolt
Work
Table
Fig 3.9 Use of stop pin
80
3.10.3 T-bolts and step blocks
The step blocks are used in combination with T-bolts and clamps to hold the work
directly on the machine table. T-bolts are fitted in the T-slots of the machine table. One side
of the clamp holds the work and the other side rests on a step of the step block. The
different steps of the block are useful in levelling the clamp when holding works of different
heights. A nut on the top of the clamp holds the work rigidly. Fig. 3.10 shows ‘T’ bolt,
clamp & step block.
‘T’ - bolt
Clamp
Step block
Work
Table
Fig 3.10 T- bolt, Clamp & Step block
3.10.4 Angle plate
Angle plate resembles the English alphabet ‘L’. It is accurately machined to have two
sides at right angles. Slots are provided on both the sides. One of the sides is bolted to the
machine table and the workpieces are held on the other side. The use of an angle plate is
shown in Fig. 3.11
Work
Angle plate
Packing
Table
Fig 3.11 Angle plate
81
3.10.5 V – block
V – block is a metal block having a ‘V’ shaped groove on it. It is used for holding
cylindrical workpieces. Operations like keyway cutting, slot cutting and machining flat
surfaces can be performed on the cylindrical workpieces held on a ‘V’ block. The use of a
‘V’ block is illustrated in Fig. 3.12.
Work
Clamp
‘V’ block
‘T’ bolt
Table
Fig 3.12 ‘V’ block
3.10.6 Special fixtures
When internal keyways are to be machined on the holes, the work is held with a
special fixture. The fixture has a V-block attached to it and the cylindrical work is mounted
on it.
3.11 Tools used in a shaping machine
The material of the cutting tool used in a shaping machine should have more hardness
and temper when compared to the material of the workpiece. So, the shaper tools are made
of the following materials
1.High Carbon Steel
2. High Speed Steel
3. Carbide tipped tool
4. Stellite tool
82
3.11.1 Types of shaper tools
According to the type of work and the type of operation, various tools are used in a
shaper. They are
Right hand ( R. H ) tool
This is a tool used for machining by moving the job from right to the left.
Left hand ( L. H ) tool
This is a tool used for machining by moving the job from left to right.
Roughing tool
When it is required to remove a good amount of material from the workpiece, roughing
tools are used. The cutting edge will be very thick, sharp and strong to withstand the cutting
pressure and to dissipate the heat generated at the cutting point. The surface obtained will
be very rough.
Round nose tool
Roughing tool
Finishing tool
Side recessing tool
Slot cutting tool
Goose neck tool
Fig 3.13 Shaper tools
83
Finishing tool
After the rough machining is performed, the finishing tool is used to obtain a very
high quality of surface finish. The cutting edge will be either flat or slightly convex. Different
types of shaper tools are shown in Fig. 3.13.
Goose neck tool
This is a special type of tool used for finish machining. Very good surface finish will
be obtained. The cutting edge of goose neck tool has a springy action. The tip of the cutting
edge lies in the same line with the rear side of the shank.
Slot cutting tool
Wide rectangular or square grooves are known as slots. Rough machining of the slot
is carried out using round nose tool. After that, a slot cutting tool is used for finish machining
work.
T-slot cutting tool
The central rectangular (or square) slot is first machined using rough machining tool
and then by using parting tool (or slot cutting tool).After that, a T-slot cutting tool is used to
machine underneath the rectangular groove.
Form tool
Form tools are made to suit some specific requirements for machining V shaped
grooves or similar special shaped grooves in concave or convex form.
3.12 Setting of shaper table, vise and toolhead
The machining accuracy will not be perfect if the machine table and toolhead are not
set properly. When the sides are perpendicular, it is referred as squareness. Parallelism
means the two sides are absolutely parallel to each other. Alignment is an arrangement in
which the relative positions of the table, the jaws of the vise, the toolhead and the ram are
perfect. The above setting of the table, work and the tool are done with the help of test bars
and feeler gauges.
3.13 Operations performed in a shaping machine
Different types of operations are performed in a shaping machine. They are broadly
classified as
1. Regular operations
2. Special operations
84
Regular operations
3.13.1 Machining horizontal
surfaces
Apron
A shaper is mostly used to
machine a flat, true surface on a
workpiece. Horizontal surfaces are
machined by moving the work mounted
on the machine table at a cross direction
with respect to the ram movement. The
clapper box can be set vertical or slightly
inclined towards the uncut surface.
This arrangement enables the tool to lift
automatically during the return stroke.
The tool will not drag on the machined
surface.
Tool
Work
Direction of feed
(work)
Fig.
3.14
illustrates
machining a horizontal surface
Fig 3.14 Machining a horizontal surface
3.13.2 Machining vertical surfaces
Apron
The feed is given to the tool by
rotating the downfeed screw of the
vertical slide. The table is not moved
vertically for this purpose. The apron is
swiveled away from the vertical surface
being machined as shown in the diagram.
Tool
Direction
of feed
(tool)
A vertical cut is made while
machining the end of a workpiece,
squaring up a block or machining a
shoulder.
Fig. 3.15 illustrates machining
a vertical surface.
Work
Fig 3.15 Machining a vertical surface
85
3.13.3 Machining angular surfaces
If the surface to be machined is neither horizontal nor perpendicular, the surface is
called inclined surface. Machining ‘V’ grooves and dovetail grooves are some examples for
angular machining.
Machining the inclined (angular) surfaces can be done in several ways. They are
a) Taper strip method
The taper strip is positioned on the table and fixed. On the taper strip, the job is
fixed and machined. The angular surface is obtained.
b) Layout method
Slanting surface is marked on the work piece. The job is positioned by suitable
arrangement in such a way that the marked line is either horizontal or vertical. If the
machining is carried out, the required angular surface is obtained.
c) Degree parallel method
Degree parallel block is a wedge shaped precision block for a particular angle. The
degree parallel block is placed first on the table. Over and above that, the workpiece is
positioned and the machining is done as usual to obtain the required angular surface.
d) Universal vice method
The job may be fixed in the universal vice and then the vice is swiveled to the
required angular position. If the machining is carried out, the required slanting (angular)
surface will be obtained.
e) Universal table method
If the universal table is available in the shaping machine, then the table can be tilted
to the required position and the work is fitted on that. The machining is done as usual to
obtain the required angular surface.
f) Swivel toolhead method
An angular cut is made at any angle other than a right angle to the horizontal or to the
vertical plane. The work is set on the table and the vertical slide of the toolhead is swiveled
to the required angle either towards left or towards right from the vertical position. The
apron is then further swiveled away from the work to be machined. Fig. 3.16 illustrates
machining an angular surface by swivel toolhead method.
86
Apron
Tool
Direction
of feed
(tool)
Work
Fig 3.16 Machining a angular surface
Special operations
Apart from machining horizontal, vertical and vertical flat surfaces, the shaping
machine can do some special machining operations. Various shaping operations are shown
in Fig. 3.17.
3.13.4 Machining dove tail groove
Dove tail joint is machined on two separate pieces of work as male and female
elements. The required shape is marked on the face of the work and the unwanted metal is
first removed by the round nose tool. A special form tool is used to finish the machining.
3.13.5 Machining a ‘V’ block
The required shape of a ‘V’ block is marked on the face of the work and machining
is done by any suitable method of angular machining.
3.13.6 Machining a tongue and groove joint
The male and female elements of the tongue and groove joint having vertical surfaces
is machined after the exact shape is marked on the face of the work.
87
Fig 3.17 Various shaper operations
1. Inclined surface 2. Concave surface 3. ‘V’ groove 4. Deep slot 5. Horizontal surface
6. Vertical surface 7. Step cut surface
3.13.7 Machining external keyways
Machining external keyways refers to the cutting of long slots along the length of
cylindrical rods. Initially a round nose tool is used and then a square nose tool is used to
finish the operation. A hole of depth equal to the depth of the keyway is made at the blind end
to leave a clearance to the tool at the end of the stroke. When a keyway is cut at the middle
of the shaft, holes are drilled at both ends of the keyway.
Tool
Work
Vice
Fig 3.18 Machining a
external keyway
88
3.13.8 Machining internal keyways
Internal keyways are cut inside the holes of gears and pulleys. It is done by holding
the tool on a special tool holder called ‘snout bar’. The snout bar is directly fitted on the the
clapper block.
Fig. 3.18 & Fig. 3.19 illustrate machining a external keyway and a
keyway respectively..
Snout bar
internal
Work
Vice
Tool
Fig 3.19 Machining internal keyway
3.13.9 T-slot machining
The shape of the T-slot is marked on the face of the work. A parting off tool is fitted
on the toolpost and a rectangular slot is machined at the middle for the required depth. The
broad base of the ‘T’ slot is machined by a T-slot cutting tool. Fig. 3.20 illustrates
machining a ‘T’ slot.
Tools
Work
Fig 3.20 ‘T’ slot cutting
89
3.13.10 Machining a rack gear
Rack gear cutting is a process of cutting teeth elements at linear pitch on a flat piece
of work. Firstly, the groove is machined with a square nose parting tool. Then, the groove
is further machined with a form tool conforming the shape of the teeth.
3.13.11 Machining irregular surfaces
A shaper can also produce a contoured surface using a round nose tool. To produce a
small contoured surface a forming tool is used. If the curve is sufficiently large, powered
crossfeed along with manual down feed is so adjusted that the tool will trace the required
contour.
3.14 Cutting speed, Depth of cut and Feed
3.14.1 Cutting speed
The distance an object travels in a particular period of time is known as speed. In a
shaper, the cutting speed is the speed at which the metal is removed by the cutting tool in a
period of one minute. In a shaper, the cutting speed is considered only during the forward
cutting stroke. This is expressed in metre per minute.
The cutting speed differs to suit different different machining conditions like work
material, the finish required, the type of the tool and the rigidity of the machine.
3.14.2 Depth of cut
Depth of cut (t) is the thickness of metal that is removed during machining. It is the
perpendicular distance measured between the machined surface and the uncut surface of the
workpiece. It is expressed in mm or in inches.
3.14.3 Feed
Feed (S) is the relative movement of the work or tool in a direction perpendicular to
the axis of reciprocation of the ram per double stroke. It is expressed in mm per stroke.
3.15 Coolant
Due to the friction between the tool and the work surface during machining, heat is
generated. The tool loses its cutting capacity and the machined surface is hardened. Coolant
is used on the surfaces to avoid damage to the cutting edge of the tool as well as to the
machined surface.
90
Soluble oil is mixed with water to be used as a suitable coolant. One part of the oil is
mixed with fifteen parts of water to be used as coolant. Usage of water as coolant may result
in rust formation on the metal parts. Lubricants cannot be used as coolants.
3.16 Safety precautions
The following safety precautions should be observed while working on a shaping
machine.
3.16.1 Safety precautions regarding operators
1. No alteration or adjustment should be done on the machine parts while the
machine is functioning.
2. Clamps holding the work should not be adjusted while the machine is in operation.
3. The machine is to be stopped before cleaning the metal chips.
4. The sharp edges of the work should be handled with care.
5. The measuring of the work should be done only after the machine is switched off.
6. The operator should not seek the assistance of others for starting and stopping the
machine.
7. Machining of precise parts and internal surfaces of the workpiece are to be
carried out with great care and attention.
8. The operator should stay away from direction of the ram movement.
3.16.2 Safety hints regarding the shaping machine
1. The workpiece is to be positioned in such a way that the ram will not hit the
workpiece while performing the forward stroke.
2. Strokelength of the ram and the position of stroke are to be set correctly before
performing the operation.
3. Proper holding of the work should be ensured. Work holding devices like clamps
and vice jaws should not come in the way of the reciprocating tool.
4. We have to ensure that the tool or the tool post or the ram will not hit the job or
the job holding clamps or the vise jaws.
5. The machine should be stopped before making any adjustment to the strokelength,
position of stroke, apron and tool position.
91
QUESTIONS
I. A. Choose the correct option
1. The shaping machine was developed by
a. Henry Maudslay
b. Eli Whitney
c. Michael Faraday
d. James Nasmith
2. The operation mainly done on a shaping machine is
a. turning
b. drilling
c. machining a flat surface
d. thread cutting
3. The mechanism used to move the shaper table automatically is
a. back gear mechanism
b. crank & slotted link mechanism
c. tumbler gear mechanism
d. ratchet & pawl mechanism
4. The part involved in reciprocation by quick return is
a. table
b. ram
c. column
d. crossrail
5. The ratio of forward stroke time to return stroke time is
a. 3 : 2
b. 5 : 3
c. 1 : 3
d. 1 : 2
I. B. Answer the following questions in one or two words
1. What type of surfaces are machined on a shaper?
2. Which stroke of the shaper is faster?
3. What is the use of ratchet & pawl mechanism?
4. What type of cutting tool is used in a shaper - a single point or a multi-point?
5. Which part of the shaper is involved in automatic lifting of the tool during return
stroke of the ram?
II. Answer the following questions in one or two sentences
1. Name any four important parts of a shaping machine.
2. What is the use of crank & slotted link mechanism?
3. Define ‘feed’ in a shaping machine.
4. Name any two points in specifying the size of a shaping machine.
5. What is the use of a clapper box?
6. What is the use of swivel toolhead of a shaping machine?
92
III. Answer the following questions in about a page
1. List out the types shaping machines.
2. Write short notes on
a. Changing the strokelength of the ram
b. Position of the ram
3. Explain any two work holding devices used in a shaping machine with diagrams.
4. List out the types of tools used in a shaping machine.
5. Explain any two operations performed in a shaping machine with diagrams.
IV. Answer the following questions in detail
1. Draw a neat diagram of a shaping machine and explain its important parts.
2. Explain the crank & slotted link mechanism of quick return of the ream with a
diagram.
3. Explain the ratchet & pawl mechnism with a diagram.
4. Explain any four work holding devices used in a shaping machine with diagrams.
5. Explain any four operations performed in a shaping machine with diagrams.
93
4. GRINDING MACHINE
4.1 Introduction
Grinding is a metal cutting operation like any other process of machining removing
metal in comparatively smaller volume. The cutting tool used is an abrasive wheel having
many numbers of cutting edges. The machine on which grinding the operation is performed
is called a grinding machine.
Grinding is done to obtanin very high dimensional accuracy and better appearance.
The accuracy of grinding process is 0.000025mm. The amount of material removed from
the work is very less.
4.2 Types of grinding machines
According to the accuracy of the work to be done on a grinding machine, they are
classified as
1. Rough grinding machines
2. Precision grinding machines
4.2.1 Rough grinding machines
The rough grinding machines are used to remove stock with no reference to the
accuracy of results. Excess metal present on the cast parts and welded joints are removed
by rough grinders. The main types of rough grinders are
1. Hand grinding machine
2. Bench grinding machine
3. Floor stand grinding machine
4. Flexible shaft grinding machine
5. Swing frame grinding machine
6. Abrasive belt grinding machine
94
4.2.2 Precision grinding machines
Precision grinders are used to finish parts to very accurate dimensions. The main types
of precision grinders are:
1. Cylindrical grinding machines
2. Internal grinding machines
3. Surface grinding machines
4. Tool and cutter grinding machines
5. Special grinding machines
4.2.3 Cylindrical grinding machine
Cylindrical grinders are generally used to grind external surfaces like cylinders, taper
cylinders, faces and shoulders of work. There are two types of cylindrical grinding machines
and they are
1. External cylindrical grinding machines
2. Internal cylindrical grinding machines
Headstock
Grinding wheel
Wheelhead
Work
Tailstock
Upper table
Lower table
Base
Fig 4.1 Cylindrical grinding machine
External cylindrical grinding machine
Cylindrical centre type grinders are intended primarily for grinding plain cylindrical
parts. Fig.4.1 illustrates a cylindrical grinder.
95
Base
The base is made of cast iron and rests on the floor. It supports the parts mounted on
it. The top of the base is accurately machined and provides guideways for the table to slide
on. The base contains the table driving mechanisms.
Tables
The tables are mounted on top of the base. There are two tables namely lower table
and upper table. The lower table slides on the guideways on the bed. It can be moved by
hand or by power within required limits.
The upper table can be swiveled upto ±10o and clamped in position. Adjustable dogs
are clamped in longitudinal slots at the side of the lower table. They are set up to reverse the
table at the end of the stroke.
Headstock
The headstock is situated at the left side of upper table. It supports the workpiece by
means of a centre and drives it by means of a dog. It may hold and drive the workpiece in a
chuck. It houses the mechanism meant for driving the work. The headstock of a universal
grinding machine can be swiveled to any required angle.
Tailstock
The tailstock is situated at the right side of the table. It can be adjusted and clamped in
various positions to accommodate different lengths of workpieces.
Wheelhead
The wheelhead may be moved at right angles to the table ways. It is operated by hand
or by power to feed the wheel to the work.The wheelhead carries a grinding wheel.
Its driving motor is mounted on a slide at the top and rear of the base. The grinding
wheel rotates at about 1500 to 2000 r.p.m.
Internal cylindrical grinding machines
Internal grinders are useful in grinding cylindrical holes and taper holes.
4.2.4 Surface grinding machines
Surface grinding machines are employed to finish plain or flat surfaces horizontally,
vertically or at any angle.
96
There are four different types of surface grinders. They are
1. Horizontal spindle and reciprocating table type
2. Horizontal spindle and rotary table type
3. Vertical spindle and reciprocating table type
4. Vertical spindle and rotary table type
Horizontal spindle surface grinding machine
The majority of surface grinders are of horizontal spindle type. In the horizontal type
of the machine, grinding is performed by the abrasives on the periphery of the wheel.
Though the area of contact between the wheel and the work is small, the speed is uniform
over the grinding surface and the surface finish is good. The grinding wheel is mounted on a
horizontal spindle and the table is reciprocated to perform grinding operation.
Base
The base is made of cast iron. It is a box like casting which houses all the table drive
mechanisms. The column is mounted at the back of the base which has guideways for the
vertical adjustment of the wheelhead.
Saddle
Saddle is mounted on the guideways provided on the top of the base. It can be moved
at cross towards or away from the column.
Table
The table is fitted to the carefully machined guideways of the saddle. It reciprocates
along the guideways to provide the longitudinal feed. The table is provided with ‘T’- slots
for clamping workpieces directly on the table or for clamping grinding fixtures or magnetic
chuck.
Wheelheead
An electric motor is fitted on the wheelhead to drive the grinding wheel. The
wheelheed is mounted on the guideways of the column, which is secured to the base. It can
be raised or lowered with the grinding wheel to accommodate workpieces of different
heights and to set the wheel for depth of cut.
Fig.4.2 illustrates a horizontal spindle surface grinding machine.
97
Column
Wheelhead
Grinding wheel
Table
Saddle
Base
Fig 4.2 Horizontal spindle surface grinder
Vertical spindle surface grinding machine
The face or sides of the wheel are used for grinding in the vertical type surface
grinders. The area of contact is large and stock can be removed quickly. But a criss-cross
pattern of grinding scratches are left on the work surface. Considering the quality of surface
finish obtained, the horizontal spindle type machines are widely used.
The grinding wheel is mounted on the vertical spindle of the machine. The work is held
on the table and grinding is done.
The base of the machine is a box like casting. The base is very similar to the one of
the horizontal spindle type. It houses all the table drive mechanisms.
98
The table is mounted on the base on top of which a magnetic chuck is mounted. A
grinding wheel is mounted on the wheelhead which slides vertically on the column. The table
is made to reciprocate or rotate to bring the work surface below the grinding wheel to
perform grinding.
Fig.4.3 illustrates a vertical spindle surface grinding machine.
Column
Wheelhead
Grinding wheel
Magnetic chuck
Table
Base
Fig 4.3 Vertical spindle surface grinder
4.2.5 Tool and cutter grinding machines
Tool and cutter grinders are used mainly to sharpen the cutting edges of various tools
and cutters. The can also do surface, cylindrical and internal grinding to finish jigs, fixtures,
dies and gauges.
Base
The base of the machine gives rigidity and stability to the machine. It is bolted rigidly
to the floor of the shop by bolts and nuts. It supports all the other parts of the machine. It is
box type and houses all the mechanisms for the saddle movements.
Saddle
The saddle is mounted directly on the top of the base and slides over it. The column is
mounted on the saddle. It can be moved up and down and swivelled to either side.
99
Table
The table resets and moves on a top base, which is mounted over the saddle. The table
has two layers. The worktable is mounted on the sub table which has ‘T’ slots for mounting
the work and attachments used on the machine. The worktable can be swiveled while
grinding tapers.
Headstock and tailstock
The headstock and tailstock are mounted on either side of the table. The workpieces
are positioned between centres and driven exactly as in a cylindrical grinder.
Wheelhead
The wheelhead is mounted on a column on the back of the machine. It can be swiveled
and positioned in the base for different set-up. A straight wheel and a cup wheel are
mounted on either sides of the wheelhead. Fig.4.4 illustrates a tool and cutter grinding
machine.
Headstock
Straight wheel
Wheelhead
Cup wheel
Tailstock
Table
Saddle
Base
Fig 4.4 Tool and cutter grinder
4.3 Size of a grinding machine
The size of a grinding machine is specified according to the size of the largest
workpiece that can be mounted on the machine.
The cylindrical centre type grinding machine is specified by the diameter and length of
the largest workpiece the machine can accommodate between centers.
100
The internal centre type grinder is specified by the diameter of workpiece that can be
swung and the maximum length of the stroke of the grinding wheel.
The reciprocating table type surface grinders are specified by the table area and the
maximum height of the grinding wheel from the table surface. The rotary table type surface
grinder is specified by the diameter of the chuck or table. A tool and cutter grinder is
specified further by the maximum size of tool that can be sharpened and dressed.
4.4 Centreless grinding
Centreless grinding is a method of grinding external cylindrical, tapered and formed
surfaces on workpieces that are not held and rotated between centres or in chucks. There
are two types of centreless grinding and they are
1. External centreless grinding
2. Internal centreless grinding
4.4.1 External centreless grinding
Two wheels - a grinding and a regulating wheel are used in external centreless
grinding. Both these wheels are rotated in the same direction. The work is placed upon the
work rest and rotated between the wheels. The feed movement of the work along its axis
past the grinding wheel is obtained by tilting the regulating wheel at a slight angle from the
horizontal. An angular adjustment of 0 to 10 degrees is provided in the machine for this
purpose. Fig. 4.5 shows centreless grinding operation.
Grinding wheel
Work
Regulating wheel
Work rest
Fig 4.5 Centreless grinding
101
4.4.2 Internal centreless grinding
The principle of external centreless grinding is applied to internal centreless grinding
also. Grinding is done on the inner surfaces of the holes. In internal centreless grinding, the
work is supported by three rolls - a regulating roll, a supporting roll and a pressure roll. The
grinding wheel contacts the inside surface of the workpiece directly opposite the regulating
roll. The distance between the contours of these two wheels is the wall thickness of the
work. Fig. 4.6 shows internal centreless grinding operation.
Pressure roll
Work
Regulating wheel
Support roll
Grinding wheel
Fig 4.6 Internal centreless grinding
4.4.3 Advantages of centreless grinding
1. As the workpiece is supported throughout the entire length , grinding is done very
accurately.
2. Small, slender and fragile workpieces can be ground easily.
3. No chucking or mounting of the work on mandrels & other holding devices are
required.
4. As the process is continuous, it is best adapted for production work.
5. The size of the work can easily be controlled.
6. A low order of skill is needed in the operation of the machine.
102
4.4.4 Diadvantages of centreless grinding
1. In hollow work, there is no certainity that the outer diameter will be concentric with
the inside diameter.
2. Works having multiple diameters are not handled easily.
4.5 Grinding machine operations
The process of grinding is the operation of removing excess material from metal parts
by a grinding wheel made of hard abrasives. The following operations are generally
performed in a grinding machine.
1. Cylindrical grinding
2. Taper grinding
3. Gear grinding
4. Thread grinding
4.5.1 Cylindrical grinding
Cylindrical grinding is performed by mounting and rotating the work between centres
in a cylindrical grinding machine. The work is fed longitudinally against the rotating grinding
wheel to perform grinding. The upper table of the grinding machine is set at 0° during the
operation.
4.5.2 Taper grinding
Taper grinding on long workpieces can be done by swiveling the upper table. If the
workpiece is short, the wheelhead may be swiveled to the taper angle. Another method of
grinding external taper is to true the face of the grinding wheel by a diamond tool dresser to
the required angle. In this case, the table and the wheelhead are not swiveled.
4.5.3 Gear grinding
The teeth of gears are ground accurately on gear grinding machines for their shape.
Gear grinding is done by the generating process or by using a form grinding wheel.
The generating process makes use of two saucer shaped grinding wheels. These
wheels are used to grind two faces of successive teeth.
The forming process makes use of formed wheels to grind a tooth at a time. This is a
very precise method of performing gear grinding.
103
4.5.4 Thread grinding
Thread grinding machines are used to grind threads accurately. The grinding wheel
itself is shaped to the thread profile. These formed grinding wheels have one or multi
threads on them.
4.5.5 Wet grinding and dry grinding
Wet grinding
The method of spreading a good quantity of coolant over the work surface and
wheel faces during grinding is known as ‘wet grinding’. Soda water is used as a coolant.
The process of grinding generates high amount of heat generally about 2000°C. Various
properties of the work material change due to the heat. In order to reduce the heat
generated during grinding, coolant is used. Wet grinding promotes long wheel life and better
look of the ground surface. Coolant is pumped from the tank through pipelines.
Dry grinding
Dry grinding is the method of doing grinding operation without applying coolant. Dry
grinding produces undesirable effects on work surfaces. It leads to burring & discoloration
of work surfaces.The cutting edges of the grinding wheel lose their cutting capacity. So, dry
grinding should better be avoided.
4.6 Grinding wheel
A grinding wheel is a multi-tooth cutter made up of many hard particles known as
abrasives having sharp edges. The abrasive grains are mixed with a suitable bond, which
acts as a matrix to manufacture grinding wheels.
According to construction, grinding wheels are classified under three categories.
1. Solid grinding wheels
2. Segmented grinding wheels
3. Mounted grinding wheels
4.6.1 Abrasives
Abrasives are used for grinding and polishing operations. It should have uniform
physical properties of hardness, toughness and resistance to fracture. Abrasive may be
classified into two principal groups.
1. Natural abrasives
2. Artificial abrasives
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4.6.2 Natural abrasives
The natural abrasives are obtained from the Earth’s crust. They include sandstone,
emery, corundum and diamond.
Sandstone is used as abrasive to grind softer materials only.
Emery is natural alumuna. It contains aluminium oxide and iron oxide. Corundum is
also a natural aluminium oxide. It contains greater percentage of aluminium oxide than
emery. Both emery and corundum have a greater hardness and abrasive action than
sandstone.
Diamond is the hardest available natural abrasive. It is used in making grinding wheels
to grind cemented carbide tools.
4.6.3 Artificial abrasives
Artificial abrasives are of two types.
1. Silicon carbide abrasives
2. Aluminium oxide abrasives
Silicon carbide
Silicon carbide is manufactured from 56 parts of silica, 34 parts of powdered coke, 2
parts of salt and 12 parts of sawdust in a long rectangular electric furnace of the resistance
type that is built of loose brick work. There are two types of silicon carbide abrasives
- green grit and black grit.
Silicon carbide is next to diamond in the order of hardness. But it is not tough enough
as aluminium oxide. It is used for grinding materials of low tensile strength such as cemented
carbides, ceramic materials, grey brass, bronze, copper, aluminium, vulcanized rubber etc.
This is manufactured under trade names of carborundum. It is denoted by the letter ‘S’.
Aluminium oxide
Aluminium oxide is manufactured by heating mineral bauxite, silica, iron oxide,
titanium oxide, etc., mixed with ground coke and iron borings in arc type electric furnace.
Aluminium oxide is tough and not easily fractured, so it is better adapted to grinding
materials of high tensile strength such as most steels, carbon steels, high speed steels, and
tough bronzes. This is denoted by the letter ‘A’.
105
4.6.4 Types of bonds
A bond is an adhesive substance that is employed to hold abrasive grains together in
the form of grinding wheels. There are several types of bonds. Different grinding wheels are
manufactured by mixing hard abrasives with suitable bonds. The table containing the types
of wheels manufatured using dufferet types of bonds and their symbols is given below
Type of bond
Symbol
Grinding wheel
1. Vitrified
V
Vitrified wheel
2. Silicate
S
Silicate wheel
3. Shellac
E
Elastic wheel
4. Resinoid
B
Resinoid wheel
5. Rubber
R
Vulcanised wheel
6. Oxychloride
O
Oxychloride wheel
4.6.5 Grain size, Grade and Structure
Grain size (Grit)
The grinding wheel is made up of thousands of abrasive grains. The grain size or grit
number indicates the size of the abrasive grains used in making a wheel, or the size of the
cutting teeth. Grain size is denoted by a number indicating the number of meshes per linear
inch of the screen through which the grains pass when they are graded. There are four
different groups of the grain size namely coarse, medium, fine and very fine. If the grit
number is large, the size of the abrasive is fine and a small grit number indicates a large grain
of abrasive.
Coarse
:
10,
12,
14,
16,
20,
Medium
:
30,
36,
46,
54,
60
Fine
:
80,
100, 120, 150,
Very fine :
220, 240, 280, 320,
106
24
180
400,
500, 600
Grade
The grade of a grinding wheel refers to the hardness with which the wheel holds the
abrasive grains in place. It does not refer to the hardness of the abrasive grains. The grade
is indicated by a letter of the English alphabet. The term ‘soft’ or ‘hard’ refers to the
resistance a bond offers to disruption of the abrasives. A wheel from which the abrasive
grains can easily be dislodged is called soft whereas the one, which holds the grains more
securely, is called hard. The grade of the bond can be classified in three categories.
Soft
:
A
B
C
D
E
F
G
H
Medium
:
I
J
K
L
M
N
O
P
Hard
:
Q
R
S
T
U
V
W
X
Y
Z
Sturcture
The relative spacing occupied by the abrasives and the bond is referred to as
structure. It is denoted by the number and size of void spaces between grains. It may be
‘dense’ or ‘open’. Open structured wheels are used to grind soft and ductile materials.
Dense wheels are useful in grinding brittle materials.
Dense
:
1
2
3
4
5
6
7
8
Open
:
9
10
11
12
13
14
15 or higher
4.6.6 Standard marking system of grinding wheels
The Indian standard marking system for grinding wheels has been prepared with a
view of establishing a uniform system of marking of grinding wheels to designate their
various characteristics.
Prefix
Manufacturer’s abrasive type symbol
First element (letter)
Type of abrasive
Second element (number)
Size of abrasive
Third element (letter)
Grade of bond
Fourth element (number)
Structure of the grinding wheel
Fifth element (letter)
Type of bond
Suffix
Manufacturer’s symbol
107
The meaning of the given marking on a grinding wheel
w
A
54
M
7
V
20
w - Manufacturer’s abrasive type symbol
A - Type of abrasive
- Aluminium oxide
54 - Size of abrasive
- Medium
M - Grade of bond
- Medium
7 - Structure of the grinding wheel
- Dense
V - Type of bond
- Vitrified
20 - Manufacturer’s symbol
4.6.7 Mounting of a grinding wheel
Great care must be taken in mounting the grinding wheels on the spindle because of
high cutting speeds. The following points are important in connection with mounting of
grinding wheel. Fig. 4.7 shows mounting of a grinding wheel.
Grinding wheel
Washer
Flange
Lead bush
Spindle
Nut
Fig 4.7 Mounting of a grinding
wheel
1. All wheels should be inspected before mounting to make sure that they have not
been damaged. The wheel is put on an arbor and is subjected to slight hammer blows. A
clear, ringing, vibrating sound must be heard.
108
2. The wheel should not be forced on and they should have an easy fit on the spindle.
3. The hole of grinding wheel is mostly lined with lead. The lead liner bushes should not
project beyond the side of wheels.
4. There must be a flange on each side of the wheel. The flange must be large enough
to hold the wheel properly, at least the flange diameter must be equal to the half of the
grinding wheel diameter. Both the flanges should be of same diameter.
5. The sides of the wheel and the flanges should be flat. Flanges contact the wheel only
with the annular clamping area.
6. Washers of compressible materials such as cardboard, leather, rubber etc., not over
1.5 mm thick should be fitted between the wheel and its flanges. The diameter of washers
may be normally equal to the diameter of the flanges.
7. The inner flange should be keyed to the spindle, whereas the outer flange should
have an easy sliding fit on the spindle so that it can adjust itself tightly to give a uniform
bearing on the wheel and the compressible washers.
8. The nut should be tightened to hold the wheel firmly. Undue tightness is unnecessary
and undesirable as excessive clamping strain is liable to damage the wheel.
9. The wheel guard should be placed and tightened before the machine is started.
10. After mounting the wheel, the machine is started. The grinding wheel should be
allowed to idle for a period of about 10 to 15 minutes. Grinding wheels must be dressed and
trued before any work can be started.
4.6.8 Glazing, Loading and Chattering
Glazing
It is the condition of the grinding wheel in which the cutting edges or the face of the
wheel takes a glass-like appearance. Glazing takes place if the wheel is rotated at very high
speeds and is made with harder bonds. Rotating the wheel at lesser speeds and using soft
bonds are the remedies. The glazed wheels are dressed to have fresh, sharp cutting edges.
Loading
The wheel is loaded if the particles of the metal being ground adhere to the wheel. The
openings or pores of the wheel face are filled up with the metal. It is caused by grinding a
softer material or by using a very hard bonded wheels and running it very slowly. It may also
take place if very deep cuts are taken by not using the right type of coolant.
109
Chattering
The wavy pattern of crisscross lines are visible on the ground surface some times. This
condition is known as chattering. It takes place when the spindle bearings are not fitted
correctly and because of the imbalance of the grinding wheel.
4.6.9 Dressing and truing of grinding wheels
Dressing
If the grinding wheels are loaded or gone out of shape, they can be corrected by
dressing or truing of the wheels. Dressing is the process of breaking away the glazed
surface so that sharp particles are again presented to the work. The common types of wheel
dressers known as “Star” -dressers or diamond tool dressers are used for this purpose.
A star dresser consists of a number of hardened steel wheels on its periphery. The
dresser is held against the face of the revolving wheel and moved across the face to dress
the wheel surface. This type of dresser is used particularly for coarse and rough grinding
wheels. Fig. 4.8 shows dressing by a star wheel dresser.
Grinding wheel
Star
dresser
Rest
Fig 4.8 Dressing of a grinding wheel (Star wheel method)
For precision and high finish grinding, small industrial diamonds known as ‘bort’ are
used. The diamonds are mounted in a holder. The diamond should be kept pointed down at
an angle of 15° and a good amount of coolant is applied while dressing. Very light cuts only
may be taken with diamond tools.
Fig. 4.9 shows dressing by a diamond tool dresser.
110
Grinding wheel
Diamond dresser
Rest
Fig 4.9 Dressing of a grinding wheel (Diamond dresser method)
Truing
The grinding wheel becomes worn from its original shape because of breaking away of
the abrasive and bond. Sometimes the shape of the wheel is required to be changed for form
grinding. For these purposes the shape of the wheel is corrected by means of diamond tool
dressers. This is done to make the wheel true and concentric with the bore or to change the
face contour of the wheel. This is known as truing of grinding wheels.
Diamond tool dreesers are set on the wheels at 15° and moved across with a feed rate
of less than 0.02mm. A good amount of coolant is applied during truing.
4.6.10 Balancing of grinding wheels
Grinding wheels rotate at high
speeds. The density and weight should
be evenly distributed throughout the
body of the wheel. If it is not so, the
wheel will not rotate with correct
balance.
The grinding wheels are balanced
by mounting them on test mandrels. The
wheel along with the mandrel is rolled
on knife edges to test the balance and
corrected.
Grinding wheel
Test mandrel
Knife
edge
Fig 4.10 Balancing of a grinding wheel
111
4.7 Cutting speed, feed and depth of cut
4.7.1 Cutting speed
Cutting speed of a grinding process is the relative speed of the grinding wheel and the
workpiece. It is expressed in m/sec.
The cutting speed of the wheel is expressed as
π dn
Cutting speed(C.S) =
----- m per sec
1000
Where:
‘d’- the diameter of the grinding wheel in mm, and
‘n’- the speed of the grinding wheel in r.p.s.
4.7.2 Feed
Feed in a grinding process is the longitudinal movement of the work mounted on the
table per revolution of the grinding wheel. It is expressed in mm per revolution.
The longitudinal feed during rough grinding is approximately 0.6 to 0.9 of the width of
the wheel and 0.4 to 0.6 of the width of the wheel during finish grinding.
4.7.3 Depth of cut
The thickness of the metal layer removed from the work in one pass of the wheel is
known as depth of cut. It is expressed in mm. Depth of cut is kept ranging from 0.005 to
0.04mm.
4.8 Surface finishing processes
In a workshop, metal parts are manufactured by performing different operations in
lathe, shaping machine, milling machine, drilling machine or grinding machine. In order to
enhance the quality of surfaces of these parts, several surface finishing processes are
performed on them. If better finish is desired for looks, for accuracy, for wearing qualities
or for better fits, one of the following processes is employed.
1. Lapping
2. Honing
3. Superfinishing
4. Polishing
5. Buffing
6. Scraping
7. Electroplating
112
4.8.1 Lapping
Lapping is the abrading process that is used to produce geometrically true surfaces,
correct minor surface imperfections, improve dimensional accuracy to provide a very close
fit between two surfaces in contact. Very thin layers of metal (0.005 to 0.01 mm) are
removed in lapping. Machining can be done to the accuracy of less than 1micron.
To perform lapping operation, lapping shoes and lapping mixture are needed. Laps
may be made of almost any material soft enough to receive and retain the abrasive grains.
They are made of soft cast iron, brass, copper or lead. It is made in different shapes.
Abrasive powders such as emery, corundum, iron oxide and chromium oxide are mixed with
oil or grease to make lapping mixture.
The face of the lap becomes charged with abrasive particles. Laps may be operated
by hands or by machine. Cylindrical work may be lapped by rotating the work in a lathe and
reciprocating the lap over the work. Flat surfaces may be lapped by holding the work
against a rotating disc. Special lapping machines like vertical lapping machine, centreless
lapping machine and abrasive belt lapping machines are also widely used.
4.8.2 Honing
Guides
Honing is the abrading process
done mostly for finishing round holed
produced by drilling, reaming or boring
by means of bonded abrasive stones
called ‘hones’. Honing is a machining
process and is used to remove metal
upto 0.25 mm. The surface roughness
value can be maintained between 0.025
and 0.4 microns. So honing is used to
correct some out of roundness, tapers,
tool marks and axial distortion.
Honing
stones
Fig. 4.11 illustrates a honing
toolhead.
Fig 4.11 Honing
113
Honing stones are used for performing honing. Honing toolhead fitted with honing
stones is fitted on spindles and rotated. The parts having holes to be honed are mounted on
vises or suitable fixtures. The spindle is moved vertically to abrade the walls of the holes. A
good quantity of coolant should be applied while honing.
Honing can be done on materials like plastic, silver, brass, aluminium, cast iron, steel
and cemented carbide. Journal bearings supporting the crank shafts and long holes found in
the barrels of guns are generally honed. The honing machines are of two types - Vertical &
Horizontal.
4.8.3 Superfinishing
The process of superfinishing is an operation intended to produce an extremely high
quality of surface finish. The surface roughness value can be maintained between 0.015 and
0.32 microns. A very thin layer of metal (0.005 mm to 0.02 mm) is removed by using very
fine size of abrasives (Size of 400 to 600)in superfinishing. It can be done on both external
and internal surfaces.
The grinding stones are made to reciprocate and the workpiece is made to rotate or
reciprocate. A fine surface is obtained by admitting coolant mixed with kerosene. Using
some special machines, superfinishing is performed on crankshaft, journal bearings and cam
shafts.
4.8.4 Polishing
Polishing is a surface finishing operation performed by a polishing wheel for the
purpose of removing metal to take out scratches, tool marks and other defects from rough
surfaces. Polishing is performed only to provide better looks. Polishing wheels are made of
leather, paper, canvas, felt or wool. The abrasive grains are setup sometimes on the faces of
the wheel and work is held against it and rotated to give the desired finish.
4.8.5 Buffing
Buffing is used to give a much higher, reflective finish that cannot be obtained by
polishing. Buffing wheels are made of felt, leather and pressed & glued layers of a variety of
cloth. The abrasive used are iron oxide, chromium oixde, emery, etc. The abrasive is mixed
with a binder. The binder is a paste consisting of wax mixed with grease, paraffin and
turpentire. It is applied either on the buffing wheel or on the work. Buffing wheels are
rotated against the work to get a superior finish.
114
4.8.6 Scraping
There will always be some minor imperfections on the machined surfaces. They are
removed by an hand tool called scraper. There are three types of scrapers - flat, half-round
and triangular. The part to be scraped is fitted in a vise and a thin layer of Persian blue is
applied on the surface. A suitable scraper is selected and circular movements are made on
the surface with it. Thin flakes of metal are removed. Persian blue is once again applied to
check the flatness.
4.8.7 Electroplating
Electroplating is the process of applying metallic coatings on the surfaces of metal
parts. It can be done on parts of non-metals also.
This is done for protection against corrosion or against wear and tear and for better
appearance. It is also done to slightly increase the size of worn out parts and to make parts
easy to solder. It may also be used to keep off selected areas on steel parts from being
carburized during heat treatment.
Common plating materials are chromium, nickel, copper, zinc, cadmium, etc. The
more precious metals like silver, gold, platinum, and radium are also applied for plating.
Door handles and automobile parts are chromium plated for appearance. The method of
plating a layer of zinc is known as galvanising.
D.C power supply
Part to be
plated
(Cathode)
Plating material
(Anode)
Electrolyte
Fig 4.12 Electroplating
115
Surfaces to be plated must be buffed smooth to eliminate scratches. The surface is
cleaned by suitable cleaning solutions to remove all grease and dirt.
The four essential elements of plating process are the part to be plated (cathode),
plating material (anode), electrolyte and direct current. The current leaves anode which is a
bar of plating metal and migrates through the electrolyte to the cathode which is the part to
be plated.
Fig 4.12 shows the method of electroplating.
4.9 Safety precautions
1. We should ensure that the work is held firmly and properly. The grinding wheel
should be inspected and mounted on the spindle.
2. Proper work speed, wheel speed and table feed should be selected according to
the nature of the work.
3. Safety goggles should be worn by the operator.
4. It should be checked whether the safety guards are fitted.
5. The operator should not touch the rotaing work or the grinding wheel.
6. The operator should not wear loose shirts and neck tie.
7. The work rest of a bench grinder should be placed close to the grinding wheel.
8. The speed of the vitrified grinding wheels should not exceed 2800 meters per
minute.
9. When new wheels are used, the wheel speed should be kept minimum.
10. If the job is held in a magnetic chuck, extra grips should be placed around the
workpieces.
116
QUESTIONS
I.A. Choose the correct option
1. The accuracy obtained by precision grinding is
a. 0.000025mm
b. 0.0025mm
c. 0.00125mm
d. 0.00625mm
2. The cutting tool with several thousands of cutting edges is
a. lathe cutting tool
b. drill
c. grinding wheel
d. milling cutter
3. The heat generated during dry grinding will be
a. 2000° C
b.20° C
c. 1000° C
d. 1200° C
4. Bond used for making elastic grinding wheel is
a. vitrified
b. silicate
c. shellac
d. resinoid
5. The grip with which the bond holds the abrasives is known as
a. grain size
b. grade of the grinding wheel
c. structure of the grinding wheel d. type of abrasive
I.B. Answer the following questions in one or two words
1. Name one artificial abrasive.
2. Name the grinding machine used for grinding jigs, fixtures and tools.
3. What is the name of the bond indicated by the letter ‘V’?
II. Answer the following questions in one or two sentences
1. What is grinding?
2. Name any four grinding machines.
3. What is centreless grinding?
4. What are the four types of surface grinders?
5. List any four operations performed in a grinding machine.
6. What are the effects of dry grinding?
7. Name any four types of bonds.
8. What is glazing?
9. What is loading?
10. What are the reasons for chattering?
117
III.Answer the following questions in about a page
1. List the types of rough and precision grinding machines.
2. Explain external centreless grinding with a diagram.
3. A grinding wheel is specified as follows w A 46 K 5 V 17 . Explain the meaning of
each symbol.
4. Explain ‘Dressing’ of a grinding wheel with a diagram.
5. Explain ‘Truing’ of a grinding wheel
6. Write short notes on
a. Lapping
b. Honing
IV. Answer the following questions in detail
1. Draw and explain a external cylindrical grinder.
2. Explain a surface grinder with a diagram.
3. Explain ‘mounting’ of a grinding wheel with a suitable diagram.
4. Write notes on
a. Precision grinding
b. Polishing
118
c. Buffing
d. Scraping
5. MILLING MACHINE
5.1
Introduction
Milling is a process of removing metal by feeding the work against a rotating multipoint
cutter. The machine tool intended for this purpose is known as milling machine.
It is found in shops where tools and cutters are manufactured. The surface obtained
by this machine tool is superior in quality and more accurate and precise.
Eli Whitney designed a complete milling machine in 1818. In the year 1861 Joseph
Brown, a member of Brown and Sharp company developed the first universal milling machine.
5.2
Advantages and disadvantages of a milling machine
5.2.1 Advantages
1. The metal is removed at a faster rate as the cutter has got multiple cutting edges
and rotates at a higher speed.
2. It is possible to perform machining by mounting more than one cutter at a time.
3. The table of the machine can be moved to an accuracy of 0.02mm.
4. It is very useful since various cutters and precise tools can be machined.
5. Special attachments can be mounted on the machine to perform operations that
are performed in other machine tools.
6. The quality of the shop is enhanced with the presence of this machine.
5.2.2 Disadvantages
1. The cost of the milling machine is high.
2. As milling cutters cost high, the investment for procuring tools is more.
3. The production cost will increase if we carry out the operations performed in a
shaper or a drilling machine with a milling machine.
119
5.3
Column and knee type milling machine
Base
It is made of cast iron and supports all the other parts of the machine tool. A vertical
column is mounted upon the base. In some machines, the base serves as a reservoir for
cutting fluid.
Column
It is mounted upon the base and is box shaped. It houses the mechanism for providing
drive for the spindle. The front vertical face of the column is machined accurately to form
dovetail guideways for the knee to move up and down. The top of the column holds an
overhanging arm.
Knee
It slides up and down on the guideways of the column. An elevating screw mounted
on the base obtains this movement. Saddle is mounted upon the knee and moves in a cross
direction.
Overhanging
arm
Table
Arbor
Arbor
support
Column
Saddle
Knee
Base
Fig 5.1 Horizontal milling machine (Pictorial view)
120
Saddle
It is mounted on the guideways of the knee and moves towards or away from the
face of the column. This movement can be obtained either by power or by hand. The top of
the saddle has guideways for the table movement.
Table
The table is moved longitudinally either by power or manually on the guideways of
the saddle. The trip dogs placed on it control the movement of the table. The table of a
universal milling machine can be swiveled horizontally to perform helical works. The top
surface of the table has got ‘T’ – slots on which the workpieces or other work holding
devices are mounted.
Spindle
It is located in the upper part of the column. It receives power from the motor through
belt, gears and clutches. The front end of the spindle has got a taper hole into which the
cutters are held with different cutter holding devices.
Overhanging arm
Spindle
Arbor support
Arbor
Column
Table
Saddle
Knee
Base
Elevating screw
Fig 5.2 Horizontal milling machine
121
Overhanging arm
It supports the arbor from the top of the column. The arbor is supported by the
bearing fitted within the arbor support. It is also useful while using some special attachments.
Front brace
It is an extra support fitted between the knee and the overhanging arm. It is slotted to
allow the knee to be adjusted vertically.
Arbor
It supports the different types of cutters used in the machine. It is drawn into the
taper hole of the spindle by a drawbolt. One or more cutters are mounted on the arbor by
placing spacing collars between them. The arbor is supported by an arbor support. The
arbor is provided with a Morse taper or self-releasing taper.
A column and knee type milling machine is illustrated in Fig. 5.1 & 5.2
Vertical milling
head
Table
Column
Saddle
Knee
Base
Fig 5.3 Vertical milling machine (Pictorial view)
122
5.3.1 Vertical milling machine
It is very similar to a horizontal milling machine in construction as it has the same
parts of base, column, knee, saddle and table. The spindle of the machine is positioned
vertically. The cutters are mounted on the spindle. The spindle is rotated by the power
obtained from the mechanism placed inside the column. Angular surfaces are machined by
swiveling the spindle head.
A vertical milling machine is illustrated in Fig. 5.3 & 5.4
Vertical milling
head
Column
Spindle
Cutter
Table
Saddle
Knee
Elevating screw
Base
Fig 5.4 Vertical milling machine
5.4
Types of milling machine
The milling machines are classified according to the general design of the machine.
1. Column and knee type
a) Plain milling machine
b) Universal milling machine
c) Omniversal milling machine
d) Vertical milling machine
2. Table type milling machine
3. Planer type milling machine
4. Special type milling machine
123
5.4.1 Column and knee type milling machine
The column of a column and knee type milling machine is mounted vertically upon the
base. Knee is mounted on the accurately machined guideways of the column. It is designed
to move up and down accurately. Saddle and table are mounted on the knee.
There are different types of column and knee type machines.
a) Plain milling machine
It is rigid and sturdy. Heavy workpieces are mounted and machined on the machine.
The work mounted on the table is moved vertically, longitudinally and crosswise against the
rotating cutter. The table cannot be rotated. It is also called as horizontal milling machine
because the cutter rotates in horizontal plane.
b) Universal milling machine
The table of a universal milling machine can be swiveled by 45º on either side and so
helical milling works can be performed. It is named so because it can be adapted for a very
vide range of milling operations.
Various milling attachments like index head, vertical milling head, slot milling head
and rotary table can be mounted. It can machine drills, reamers, gears, milling cutters with a
very high degree of accuracy and so it finds an important place in a workshop.
c) Omniversal milling machine
In addition to the table movements obtained in a universal milling machine, the knee
can be tilted to a required angle. It is useful for machining helical grooves, reamer and bevel
gears. It is mostly used in tool room work.
d) Vertical milling machine
A spindle of a vertical milling machine is positioned at right angles to the table. The
cutter is moved vertically or at an angle by swiveling the vertical head of the machine.
The machine is adapted for machining slots and flat surfaces by moving the table. By
mounting end mills and face milling cutters on the spindle, vertical milling and internal milling
are preformed.
124
5.4.2 Differences between a plain milling machine and a universal
milling machine
Plain milling machine
Universal milling machine
1. The table can be moved vertically,
longitudinally and crosswise.
1. Apart from the three movements of a
plain milling machine, it can be swiveled
about 45º.
2. Helical milling works cannot be done
as the tablecannot be swiveled.
2. The table can be swiveled and helical
milling and spiral milling can be
performed.
3. As there are no special attachments,
operations like gear cutting, slotting and
vertical milling cannot be performed.
3. Special attachments like indexing
head, rotary table, vertical milling
attachment, slotting head are available
with this machine. So spur gear, helical
gear, bevel gear, cutters and reamers can
be machined.
4. It is more rigid and suitable for
machining on heavy and large
workpieces and for simple milling
operations.
4. It is meant for light workpieces. A vide
range of operations can be performed in
this machine. It is mainly used in tool
rooms.
5. The cost is less.
5. It is very costly.
5.5
Size of a milling machine
The size of a milling machine is specified as follows
1. The size of the table (length and width)
2. The maximum lengths of longitudinal, cross and vertical travel of the table.
3. Number of spindle speeds, number of feeds
4. Spindle nose taper
5. Power required
6. Nett weight of the machine
7. The floor space required
8. Type of the machine
125
5.6 Fundamental milling processes
The various milling processes may be grouped under two headings:
1. Peripheral milling
2. Face milling
5.6.1 Peripheral milling
The machining is performed by the cutting edges on the periphery of the milling cutter.
It is classified under two headings
1. Up milling
2. Down milling
Up milling
In this method, the workpiece mounted on the table is fed against the direction of
rotation of the milling cutter. The cutting force is minimum during the beginning of the cut and
maximum at the end of cut. The thickness of chip is more at the end of the cut. As the cutting
force is directed upwards, it tends to lift the workpiece from the fixtures. A difficulty is felt in
pouring coolant on the cutting edge. Due to these reasons the quality of the surface obtained
by this method is wavy. This processes being safer is commonly used and sometimes called
conventional milling.
Cutter
Work
Work
Downmilling
Upmilling
Fig 5.5 Upmilling and down milling
Down milling
The workpiece mounted on the table is moved in the same direction as that of the
rotation of the milling cutter. The cutting force is maximum at the beginning and minimum at
the end of cut. The chip thickness is more at the beginning of the cut. The workpiece is not
disturbed because of the bite of the cutter on the work. The coolant directly reaches to the
cutting point. So the quality of surface finish obtained is high. Because of the backlash error
between the feed screw of the table and the nut, vibration is setup on the workpiece.
Fig. 5.5 illustrates up milling & down milling.
126
5.6.2 Face milling and end milling
During face milling, the machining is performed by the peripheral cutting edges. The
surface obtained by the processes is perpendicular to the axis of rotation of the cutter.
End milling is a process of the machining by milling cutters which have cutting edges
both on the end face and on the periphery.
5.7 Work holding devices
For effective machining operations, the workpieces need to be properly and securely
held on the machine table. The following are the usual methods of holding work on the
table.
Large and irregular shaped workpieces are held on the milling machine table by
‘T’ – bolts and clamps.
‘V’ – blocks are used for holding cylindrical workpieces on the machine table in
which keyways, slots and flats are to the machined. Angle plates are used to support the
work when surfaces are to be milled at right angles to another machined surface.
Work
Movable jaw
Fixed jaw
Fig 5.6 Plain vise
Vises are commonly used for holding work on the table due to its quick loading and
unloading arrangement. There are mainly three types of vises namely plain vise, swivel vise
and universal vise. Different types of vises are shown in Fig. 5.6, 5.7 & 5.8.
Work
Swivel base
Fig 5.7 Swivel vise
127
Tilting base
Clamping nut
Swivel base
Fig 5.8 Universal vise
Milling fixtures are useful when large numbers of identical workpieces are to be
machined. Workpieces are held easily, quickly and accurately by milling fixtures.
5.8
Cutter holding devices
Depending on the design of the cutter, there are several methods of supporting milling
cutters on the machine spindle.
1) Arbor
2) Collet
3) Adapter
4) Screwed on cutters
5.8.1 Arbor
Milling cutters with central holes are mounted and keyed on a shaft called arbor.
There are three different types of arbor namely Pilot end arbor, ‘A’ type arbor and stub
arbor.
The arbors are made with taper shanks for correct alignment with the machine spindle.
The left side of the arbor is threaded internally to receive a drawbolt. This drawbolt connects
the arbor with the spindle. A long key way is cut on the entire length of the arbor. Cutters are
mounted at desired positions on the arbor by placing spacing collars between them. The
spindle rotation is transmitted to the arbor and the cutter is rotated.
An arbor is illustrated in Fig. 5.9
128
Spacing
collars
Draw bolt
Taper shank
Cutter
Bearing
Fig 5.9 Arbor
5.8.2 Collet
It is a form of sleeve bushing used to hold arbors or cutters having a smaller shank
than the spindle taper. Collets are connected to the spindle by a drawbolt and the rotary
motion is transmitted to the cutters. Fig. 5.10 shows a collet.
Fig 5.10 Collet
5.8.3 Adapters
Milling cutters having shanks are generally mounted on adapters. The outside taper
of the adapter conforms to the taper hole of the spindle. The shank of the cutter fits into the
taper hole of the adapter. An adapter is shown in Fig. 5.11
Fig 5.11 Adapter
129
5.8.4 Screwed arbor
The small cutters having threaded holes at the center are held by screwed arbors. It
has a threaded nose at one end and a taper shank at the other end. The shank of the arbor is
mounted on the spindle. A Screwed arbor is illustrated in Fig. 5.12.
Cutter
Arbor
Fig 5.12 Screwed arbor
5.9
Milling machine attachments
The milling machine attachments are intended for the purpose of developing the range
of operations, versatility, production capacity and accuracy of machining process. The
different milling machine attachments are:
1)
Vertical milling attachment
2)
Universal milling attachment
3)
High speed milling attachment
4)
Slotting attachment
5)
Rotary table attachment
6)
Indexing head attachment
5.9.1 Vertical milling attachment
A horizontal milling machine is converted into a vertical milling machine by the vertical
milling attachment. Vertical milling attachment is mounted on the face of the column of the
horizontal milling machine. The attachment along with the spindle can be swiveled to any
angle for machining angular surfaces.
5.9.2 Universal milling attachment
By having the universal milling attachment, the spindle of the machine can be swiveled
about two perpendicular axes. This arrangement permits the spindle axis to be swiveled at
practically any angle to machine any angular surface of the work. This attachment is supported
to the over arm to operate it at higher spindle speeds.
130
5.9.3 High speed milling attachment
This attachment is used to increase the regular spindle speeds by four to six times.
Milling cutters of smaller diameters are operated efficiently at higher cutting speeds. This
attachment is bolted to the face of the column and enables the cutter to be operated at
speeds beyond the scope of the machine.
5.9.4 Slotting attachment
The rotary movement of the spindle is converted into reciprocating movement of the
ram by a crank arrangement. This attachment makes the milling machine to be converted
into a slotting machine by accepting a single point slotting tool. The tool is mounted on the
ram and used for cutting internal or external keyways, splines etc., It can also be swiveled to
machine angular surfaces.
5.9.5 Rotary table attachment
It is a special device bolted on top of the machine table to provide rotary motion to
the workpiece in addition to the longitudinal, cross and vertical movements of the table. It
consists of a circular table provided with ‘T’ – slots mounted on a graduated base. The
driving mechanism of this attachment is made possible by a worm and worm gear.
5.9.6 Indexing head attachment
It is a special work holding device used for dividing the periphery of the work into
any number of equal divisions. The work is held in a chuck of the dividing head spindle or
supported between centers. It is also used in shaping machines and slotting machines. While
machining gears, spirals, clutches and ratchets, this dividing head is used to divide the
circumference of the work into any number of equal parts.
5.10 Standard milling cutters
There are different types of milling cutters used in a milling machine. A suitable milling
cutter is selected according to the need. They are
1. Plain milling cutter
2. Side milling cutter
3. Metal slitting saw
4. Angle milling cutter
5. End milling cutter
6. ‘T’ – Slot milling cutter
7. Fly cutter
8. Formed cutter
131
5.10.1 Plain milling cutter
Plain milling cutters are cylindrical in shape and have teeth on the circumferential
surface only. They are used for producing flat surfaces parallel to the axis of rotation of the
spindle. The teeth of the cutter may be straight or helical according to the size. If the width
of the cutter is more, it is called as slabbing cutter or cylindrical milling cutter. They have a
central hole in order to be mounted on the arbor. Plain milling cutters have nicked teeth to
break the chips into small pieces. Helical plain milling cutters are superior to a straight plain
milling cutter. A plain milling cutter is illustrated in Fig. 5.13 & 5.14.
Plain milling cutter
Side and face milling cutter
Fig 5.13 Pictorial views of milling cutters
5.10.2 Side milling cutter
Side milling cutters have teeth on its periphery and also on one or both of its sides.
They are intended for removing metal from the sides of the workpiece. There are different
types of side milling cutters namely face and side milling cutter, half side milling cutter,
staggered teeth side milling cutter, and interlocked side milling cutter. Machining is performed
by selecting a proper milling cutter. A side milling cutter is illustrated in
Fig. 5.13 & 5.15.
Fig 5.14 Plain milling cutter
132
Fig 5.15 Side milling cutter
5.10.3 Metal slitting saw
It is intended for cutting narrow, deep slots and for parting off operation. The teeth
are cut on the circumference of the cutter. The width of the cutter is limited. The outside
diameter of the cutter will be upto 200mm and width of the cutter ranges from 0.75mm to
7mm. The side of the cutter is relieved so that the side may not rub against the work.
A metal slitting saw is illustrated in Fig. 5.16.
Fig 5.16 Metal slitting saw
133
5.10.4 Angle milling cutter
The teeth of the angle milling cutter are not parallel to the axis but are at an angle to
it. By using angle milling cutter, inclined surfaces, bevels and helical grooves are machined.
There are two types of angle milling cutter – Single angle milling cutter and double angle
milling cutter. Fig. 5.17 shows a single angle milling cutter.
Fig 5.17 Angle milling cutter (Single)
5.10.5 ‘T’ – Slot milling cutter
It is a special form of end mills intended for machining ‘T’- slots. It looks like a side
milling cutter with a shank. The cutters have cutting teeth on the periphery as well as on both
sides of the cutter. Fig. 5.18 shows a ‘T’ – Slot milling cutter.
5.10.6 End mill
These cutters have cutting
teeth on the end as well as on the
periphery of the cutter. It is made
of two parts – body and shank.
The shanks of the cutter may be
straight or taper. If the cutter
doesn’t have a shank it is called
shell end milling cutter. These
cutters are useful in machining long
narrow slots, holes and flat
surfaces. A End mill is illustrated
in Fig. 5.19.
Fig 5.18 ‘T’ slot milling cutter
134
Fig 5.19 End milling cutters
A - Taper shank B - Straight shank
5.10.7 Fly cutter
Fly cutter is the simplest form of cutter. It consists of a single point cutting tool
attached to the end of the arbor. The cutting edge may be formed to reproduce a contoured
surface. They are used when standard cutters are not available. The work is done very
slowly because of a single cutting edge. A fly cutter is shown in Fig. 5.20.
Arbor
Single point cutting tool
Work
Fig 5.20 Fly cutter
5.10.8 Formed cutter
Formed cutters have irregular profiles on their cutting edges to produce required
outlines on the work. Concave and convex milling cutters are used to produce convex and
concave surfaces respectively. Using gear milling cutters, gears are machined. Corner round
milling cutters are used for cutting a radius on the edges of the work. With the help of thread
milling cutters threads are milled to a specific form and size. Tap and reamer cutters are
used for producing grooves or flutes in taps and reamers.
135
5.11 Elements of a plain milling cutter
The main parts and angles of a plain milling cutter as shown in Fig. 5.21 are described
below:
Body of cutter: It is the part of the cutter left after exclusion of the teeth.
Face: The portion of the teeth next to the cutting edge is known as face.
Land: The relieved back portion of the tooth adjacent to the cutting edge. It is relieved
to avoid interference between the surface being machined and the cutter.
Outside diameter: The diameter of the circle passing through the peripheral cutting
edges.
Central hole: It refers to the hole present at the centre of the cutter. A keyway is cut
inside the hole
Relief angle
Primary clearance angle
Cutting edge
Secondary clearance angle
Land
Rake angle
Face
Central hole
Depth of the
tooth
Fig 5.21 Nomenclature of a plain milling cutter
136
Cutter angles
Relief angle: It is angle the between the land of the tooth and the tangent to the
outside diameter of the cutter at the cutting edge of the particular tooth. (approx 7.5 °)
Primary clearance angle: It is the angle between the back of the tooth and the
tangent drawn to the outside diameter of the cutter at the cutting edge. (approx 15 °)
Secondary clearance angle: It is the angle formed by the secondary clearance
surface and the tangent to the periphery of the cutter at the cutting edge.
Rake angle: The angle measured in the diametral plane between the face of the
tooth and a radial line passing through the cutting edge of the tooth. The rake angles may be
positive, negative or zero. If the face and the tooth body are on the same side of the radial
line, the rake angle between the radial line and the tooth face is positive.The tooth face and
tooth body may be on opposite sides of the radial line. Then the rake angle is negative. If
the radial line and the tooth face coincide in the diameter plane the rake angle is zero.
5.12 Milling cutter materials
The milling cutters are generally made of the following materials.
1. Tool steel - High speed steel (HSS)
- High carbon steel (HCS)
2. Cemented carbide
3. Stellite
In general shop work, the high speed steel cutters are most widely used.
5.13 Milling machine operations
The following operations are performed using suitable milling cutters.
1. Plain milling
9. Flute milling
2. Face milling
10. Keyway milling
3. Side milling
11. Drilling & reaming
4. Straddle milling
12. Boring
5. Angular milling
13. Gear cutting
6. Gang milling
14. Thread milling
7. Form milling
15. Cam milling
8. End milling
137
5.13.1 Plain milling
It is the operation of production of a flat surface parallel to the axis of rotation of the
cutter. It is also called as slab milling. Plain milling cutters and slab milling cutters are used to
perform this operation. Fig. 5.23 shows plain milling operation.
Slab milling cutter
Work
Fig 5.22 Plain milling operation
5.13.2 Face milling
The face milling is the operation performed by the face milling cutter rotated about an
axis at right angles to the work surface. End mills and side & face milling cutter are also used
at times to perform this operation. The depth of cut is provided to the table. Fig. 5.23
shows face milling operation.
Face milling
cutter
Work
Fig 5.23 Face milling
operation
138
5.13.3 Side milling
Side milling is the operation of machining a vertical surface on the side of a workpiece
by using a side milling cutter.
Side & face
milling cutters
5.13.4 Straddle milling
It is the operation of
production of two vertical
surfaces on both sides of the
work by two side milling cutters
mounted on the same arbor. By
using suitable spacing collars,
the distance between the two
cutters is adjusted correctly.
The straddle milling is commonly
used to produce square or
hexagonal surfaces.
Fig. 5.24 shows
straddle milling operation.
Work
Fig 5.24 Straddle milling operation
Angle milling cutter
Work
Fig 5.25 Angular milling
operation
139
5.13.5 Angular milling
Production of an angular surface on a workpiece other than at right angles to the axis
of the milling machine spindle is known as angular milling. Example of angular milling is the
production of the ‘V’ blocks. Fig. 5.25 shows angular milling operation.
Milling cutters
5.13.6 Gang milling
It is the operation of
machining several surfaces of
work simultaneously by
feeding the table against a
number of cutters (either of
same type or of different
type) mounted on the arbor
of the machine. This method
saves much of machining time
and mostly used in production
work. Fig. 5.26 shows gang
milling operation.
Work
Fig 5.26 Gang milling operation
Form milling
cutter
Work
Fig 5.27 Form milling operation
5.13.7 Form milling
The form milling is the operation of production of irregular contours by using form
cutters. Machining convex and concave surfaces and gear cutting are some examples of
form milling. Fig. 5.27 shows form milling operation.
140
5.13.8 End milling
End milling cutter
It is the operation of
producing a flat surface which may
be vertical, horizontal or at an
angle to the table surface. The end
milling is performed by a cutter
known as an end mill. End milling
is mostly performed in a vertical
milling machine.
Work
Fig. 5.28 shows end
milling operation.
Fig 5.28 End milling operation
5.13.9 Flute milling
Flute milling is performed by selecting a suitable cutter in a milling machine. The flutes
found on the drills, reamers and taps are machined by this method.
5.13.10 Keyway milling
The operation of production of keyways, grooves and slots of different shapes and
sizes can be performed in a milling machine by using a plain milling cutter, a metal slitting
saw, an end mill or by a side milling cutter.
5.13.11 Drilling and reaming
The operation of drilling and reaming are performed in a milling machine by mounting
drills and reamers into the spindle of the machine.
5.13.12 Boring
A single point cutting tool is mounted on the arbor to perform boring. By adjusting
the single point cutting tool radially, different diameters of bores are machined.
5.13.13 Gear cutting
Gear cutting operation is performed in a milling machine by using a form cutter. The
work is held between centers on a universal dividing head. A proper gear cutter is selected
and the teeth are cut by DP, module method.
141
5.13.14 Thread milling
This operation is performed in a special thread milling machine by rotating both the
work and the cutter. Several cuts are made to cut the threads to their depth.
5.13.15 Cam milling
Cam milling is the operation of producing cams in a milling machine with the use of a
universal dividing head and a vertical milling attachment. It is performed by end mills on the
cam blank.
5.14 Cutting speed, feed and depth of cut
5.14.1 Cutting speed
It is the distance travelled by a point on the cutting edge of the milling cutter to
remove metal in time duration of one minute. It is expressed in meters per minute.
π DN
Cutting Speed= ————
1000
Where:
meter / minute
D = The diameter of the milling cutter in mm
N = Spindle speed in rpm
The cutting speed depends upon the material to be machined, the cutter material,
depth of cut, feed, type of operation and the coolant used.
Example: Calculate the cutting speed to perform milling with a cutter of diameter
60mm and spindle speed of 250rpm.
Solution:
Given: Diameter of cutter
Spindle speed
π DN
Cutting Speed= ————
1000
(D)
= 60 mm
(N)
= 250 rpm
meter / minute
22 x 60 x 250
= ———————————
7 x 1000
= 47.14 metre / minute
142
5.14.2 Feed
The feed in a milling machine is defined as the distance the workpiece advances
under the cutter. Feed can be expressed in three different methods:
1. Feed per tooth: It is the distance the work advances in the time between
engagements by the two successive teeth. It is expressed in mm per tooth.
2. Feed per cutter revolution: It is the distance the work advances in the time
when the cutter turns through one complete revolution. It is expressed in mm per revolution
of the cutter.
3. Feed per minute: It is the distance the work advances in one minute. It is
expressed in mm per minute.
The feed in a milling machine depends on the material to be machined, cutter material,
depth of cut, cutting speed, type of operation and the rigidity of the machine.
5.14.3 Depth of cut
The depth of cut is the thickness of the material removed in one pass of the work
below the cutter. It is expressed in mm.
5.15 Indexing head
Indexing is the method of dividing the periphery of a piece of work into any number
of equal parts. The attachment used for performing indexing is known as indexing head.
The indexing operation can be adapted for cutting gears, ratchet wheels, keyways, fluted
drills, taps and reamers. The indexing head serves as an attachment for holding and indexing
the work in doing the above tasks. There are three different types of indexing heads namely
1. Plain or simple dividing head
2. Universal dividing head
3. Optical dividing head.
5.15.1 Construction of indexing head
The construction of a universal dividing head as shown in Fig. 5.29 & 5.30 is
explained below:
Base
The base of the indexing head is fitted in the ‘T’ – slots of the milling machine table.
It supports all the other parts of dividing head.
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Worm gear
Spindle
Centre
Index
plate
Worm
Worm shaft
Handle
Concentric
hole circles
Sector arms
Index
plate
Crank pin
Fig 5.29 Construction of a index head
Spindle
The spindle is situated at the centre of the dividing head. It has a taper hole to
receive a live center. The spindle is supported on a swiveling block, which makes the spindle
to be tilted through any angle from 5º below horizontal to 10º beyond vertical. A worm
wheel is mounted on the spindle. While doing direct or rapid indexing, the index plate is
directly fitted on the front end of the spindle nose.
Worm shaft
It is situated at right angles to the main spindle of the dividing head. A single threaded
worm is mounted on the worm shaft, which meshes with the worm wheel. An index plate is
fitted on the front end of the worm shaft and with the help of a handle the worm shaft can be
rotated to a predetermined amount.
144
Index plate
It is mounted on the front end of the worm shaft. It is a circular disk having different
numbers of equally spaced holes arranged in concentric circles. The crank is positioned in
the required hole circle and rotated through a calculated amount while indexing. The sector
arm is used to eliminate the necessity of counting the holes on the index plate each time the
index crank is moved.
Index plate
Index head
Spindle
Tailstock
Crank
Fig 5.30 Index head
Driven shaft
It is parallel to the spindle and perpendicular to the worm shaft.
Dead center
The work is held between the center of the spindle and the dead center. It can be
made to slide and positioned at the required location.
5.15.2 Working principle of dividing head
When the crank is rotated with help of a handle through the required number of holes
in the index plate, the work is rotated to required amount. This is possible because of the
worm and worm wheel mechanism.
A gear train is arranged between the main spindle and the driven shaft when indexing
is done by differential indexing method. The work is rotated as usual when the handle is
rotated. At the same time, the index plate is also made to rotate a small amount through the
gear train. When indexing is by this differential indexing method, the index plate is released
from the lock pin.
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5.16 Indexing methods
There are several methods of indexing and they are
1. Direct or rapid indexing
2. Plain or simple indexing
3. Compound indexing
4. Differential indexing
5. Angular indexing
5.17 Safety precautions
Before operating the milling machine, the operator should know how to operate
various controls of the machine. It should be ensured that the workpiece is held rigidly on
the milling machine table. The cutter should not be in contact with the work even before the
machining is commenced. The spindle speed of the machine should not be altered when the
machine is in operation. When the power of the machine is ‘ON’, the arbor nut should not
be removed or tightened. The operator should keep his body away from the rotating cutter.
No steps should be taken to measure the workpiece while the cutter is cutting or revolving
near the workpiece. When the machine is in operation, safety guards should be placed in
their positions to prevent coolant and metal chips from spilling out.
The metal chips should be removed with suitable brushes and not with bare hands.
The operator should seek assistance from others while handling special attachments and
heavy workpieces. The operator should always be present in person at the machine tool
when the machine is in operation.
The machine tool should always be started and stopped by the operator himself.
Dangers can be averted by handling the cutters with sharp cutting edges with great care. The
machine tool should be kept clean. Milling cutters and measuring instruments should not be
placed on the machine.
The attention of the operator should always be focussed on the task only. When
troubles happen in the machine, they should be corrected with the assistance of proper
technicians. In general, safety should be ensured to the operator, the workpiece and the
cutting tool.
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QUESTIONS
I .A Choose the correct option
1. Milling machine was developed by
a. Henry Maudslay
b. Eli Whitney
c. James Nasmith
d. Michael Faraday
2. In a milling machine, cutters are mounted on
a. column
b. spindle
c. overhanging arm d. arbor
3. The amount of table travel is controlled by
a. saddle
b. trip dogs
c. cross-slide
d. elevating screw
4. The distance travelled by a point on a milling cutter in one minute is known as
a. cutting speed
b. depth of cut
c. spindle speed
d. feed
I.B. Answer the following questions in one or two words
1. What is the base of a milling machine made of ?
2. Name the part which holds the other end of the arbor in a milling machine.
II. Answer the following questions in one or two sentences
1. What is milling?
2. What are the types of milling machines?
3. How is the size of a milling machine specified?
4. Name the fundamental milling processes.
5. What are the types of peripheral milling?
6. Name four work holding devices in a milling machine.
7. What is indexing?
8. What is the use of indexing head?
9. What are the types of indexing head?
10. What are the methods of indexing?
III. Answer the following questions in about a page
1. What are the differences between a plain milling machine and a universal milling machine?
2. List out various milling machine attachments.
3. Name the milling cutters.
4. What are the different milling machine operations?
IV. Answer the following questions in detail
1. Draw a neat diagram of a milling machine and explain its construction.
2. Explain - Upmilling, Down milling.
3. Explain any four cutter holding devices with diagrams.
4. Draw a neat diagram of a plain milling cutter and explain its nomenculature.
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6. HYDRAULIC EQUIPMENTS
6.1 Introduction
The volume of a liquid cannot be changed by applying pressure. This property of
liquids forms the base of study of hydraulics. In modern metal working plants, hydraulic
pressure is being used to operate practically every type of machine tool.
6.2 Hydraulic pumps
Hydraulic pump is a device, which transforms mechanical energy into hydraulic energy.
It serves as the heart of the hydraulic circuit. It provides the force used to move the load in
the circuit but the pressure of the circuit is not developed by the pump. The pressure built up
in a circuit is because of the quantity of the oil or the setting of the pressure relief valve.
6.2.1 Principle of a hydraulic pump
Every hydraulic pump has an inlet and an outlet. Partial vacuum is created at the inlet
port because of the rotation of the impeller. Hydraulic liquid is forced to flow from the
reservoir because of this vacuum through a pipeline and is pumped out through the outlet.
6.2.3 Size of the pump
The size of the pump is specified by the quantity of the oil to be pumped, suction head
(the depth from which oil is to be sucked) and the delivery head (the height upto which oil is
to be pumped).
6.3 Types of hydraulic pump
Hydraulic pumps are classified according to three different features
A. According to the displacement of hydraulic liquid
i) Positive displacement pump
ii) Non-positive displacement pump
B. According to the volume of outlet
i) Constant delivery pump
ii) Variable delivery pump
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C. According to the nature of movement of the moving part
i) Rotary pump
ii) Reciprocating pump.outlet
6.3.1 Features of positive displacement pump
1. It can pump against high pressures.
2. It can handle small amount of oil at high pressures
3. When the pump is working against high pressures, the volume of the outlet will not
have any slip. So the outlet should not be closed while pumping as it will cause damage to
the pump. A pressure relief valve is connected to the circuit next to this pump.
4. This pump has got self priming (The pump can draw liquid from the reservoir).
6.3.2 Features of non-positive displacement pump
1. It cannot pump against high pressure.
2. It can handle more amount of oil at low pressure.
3. A slip in volume will be felt when the pump is working against at high pressures.
Even if the outlet is closed, it will not cause any damage to the pump.
4. Self-priming is not possible.
6.4 Centrifugal pump
6.4.1 Types of centrifugal pump
A. According to head of liquid
a. Low lift pump
b. Medium lift pump
c. High lift pump
B. According to type of the casing
a. Volute casing pump
b. Vortex casing pump
c. Diffuser casing pump
C. According to number of impellers
a. Single stage pump
b. Multi stage pump
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D. According to the type of impeller
a. Closed impeller pump
b. Semi-open impeller pump
c. Open impeller pump
E. According to direction of flow of oil
a. Radial flow type
b. Axial flow type
c. Mixed flow type
Fig. 6.1 shows the types of casings of a centrifugal pump.
Vortex casing
Volute casing
Diffuser ring casing
Fig 6.1 Types of centrifugal pumps (according to the type of the casing)
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Closed type
Semi-open type
Open type
Fig 6.2 Types of centrifugal pumps (according to the type of impeller)
Radial flow
Axial flow
Mixed flow
Fig 6.3 Types of centrifugal pumps (according to the direction of flow of liquid)
Fig. 6.2 shows the types of impellers of a centrifugal pump. Fig.6.3 shows
various methods of flow of liquid in a centrifugal pump.
6.4.2 Main components of a centrifugal pump
1. Prime mover
2. Impeller
3. Casing
4. Suction pipe
5. Delivery pipe
Prime mover
The prime mover of a pump shall be an electric motor or a oil engine. It provides the
rotational power to the shaft of the device.
151
Impeller
It is the rotating part of the device. Vanes or blades are arranged in series on it. The
vanes are fitted on the shaft and rotated by the prime mover.
Casing
Casing is a hollow chamber surrounding the impeller. It is made as an air-tight unit.
The sectional area of the casing gradually increases in the direction of the flow of liquid. This
construction ensures the decrease in the velocity of the liquid and increase of the pressure.
Outlet
Casing
Impeller
Inlet
Foot valve
Fig 6.4 Centrifugal pump
152
Suction pipe
The top of the suction pipe is connected to the impeller (inlet). The bottom end is
attached with a foot valve and a strainer.
Delivery pipe
The lower end of the delivery pipe is connected to the outlet of the pump. The liquid
is pumped out through the other end of the pipe.
6.4.3 Working of centrifugal pump
Before the pump is set on for pumping, priming is done. Priming is done by filling water
in the suction pipe and the impeller. While doing so, the air valve is opened. As a result, no
air pocket is left in the casing. The presence of any air will certainly decrease the sucking
capacity of the impeller.
After the priming is over, the pump is started. The prime mover operates the impeller.
The vanes on the impeller creates centrifugal force inside the casing. Vacuum is created at
the centre of the impeller(eye). Water from the reservoir reaches the casing through the
inlet. Due to the centrifugal force, water is thrown radially outwards. As the sectional area of
the casing gradually increases, velocity energy of the liquid is transformed into pressure
energy. The liquid with increased pressure is pumped to a required height through the outlet.
As the impeller goes on rotating, more water is pumped out.
Fig. 6.4 illustrates the working of a centrifugal pump.
6.4.4 Applications of centrifugal pump
1. Water pumphouses
2. Sewage treatment
3. Irrigation
4. Oil refineries
6.4.5 Advantages and disadvantages of centrifugal pump
1. Durability
2. Low cost
3. Suitable for pumping coolant
4. Low efficiency
5. Limited to be used at low pressure
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6.5 Reciprocating pump
Reciprocating pump is one in which the liquid is pumped by the reciprocating action of
the moving part known as a piston or a plunger inside a cylinder.
6.5.1 Types of reciprocating pump
A. According to the shape of the reciprocating part
a. Piston pump
b. Plunger pump
B. According to the action of the liquid
a. Single acting pump
b. Double acting pump
C. According to number of cylinders
a. Single cylinder pump
b. Multi cylinder pump
6.5.2 Components of a reciprocating pump
1. Cylinder
2. Piston
3. Connecting rod
4. Crank
5. Suction pipe
6. Suction valve
7. Delivery pipe
8. Delivery valve
Cylinder
Cylinder is a hollow part inside of which is accurately machined. Piston reciprocates
within the cylinder.
Piston
Piston is the reciprocating part of the pump. A connecting rod is connected to it on one side.
Connecting rod
Connecting rod is attached to piston on one end and with a crank on the other end.
It converts the rotary motion of the crank into reciprocating motion of the piston.
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Outlet
Outlet valve
Piston
Cylinder
Connecting shaft
Inlet valve
Inlet
Fig 6.5 Reciprocating pump
6.5.3 Working of a reciprocating pump
When the crank is made to rotate by means of prime mover, the piston reciprocates
within the cylinder to pump out the liquid.
Suction stroke
As shown in Fig. 6.5, when the piston starts moving towards right, a vacuum is
created on the left of the cylinder. The suction valve opens and the liquid is sucked through
the suction pipe into the cylinder. The delivery valve remains closed at this stage.
Delivery stroke
Due to the rotation of the crank, piston is moved towards left. The piston exerts
pressure on the liquid inside the cylinder and the delivery valve opens. The liquid is thrown
through the delivery pipe with pressure. At this stage, the suction valve remains closed.
On continuous reciprocation of the piston, liquid is sucked and pumped contiuously.
155
6.5.4 Applications of reciprocating pump
1. Pumping sea water, ship and marine field
2. Air pumping devices
3. Filling water in small grade boilers
4. Oil pumping
6.5.5 Differences between a centrifugal pump and a reciprocating
pump
Centrifugal pump
Reciprocating pump
1. Handles high volumes of liquid.
1. Handles less volumes of liquid.
2. Practically handles all types of liquid oil, sewage, chemicals, paper pulp,
jaggery and liquids of high viscosity.
2. Used for pumping pure liquids and
liquids with low viscosity
3. Rotates at higher speeds
3. Moves at a slow speed.
4. Not provided with suction valve and
delivery valve.
4. Provided with suction valve and
delivery valve.
5. The discharge of liquid is contiuous.
5. The discharge is pulsating.
6. Less maintenance cost.
6. High maintenance cost.
7. Less weight.
7. The weight is relatively high.
8. Occupies less space.
8. Requires more space.
9. Consists of few simple parts.
9. Complicated parts.
10. The efficiency is low.
10. The efficiency is high.
6.6 Rotary pumpumps
The types of rotary pumps are
1. Gear pump
2. Vane pump
3. Lobe pump
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6.6.1 Gear pump
In a gear pump, two gears are placed inside a hollow casing in such a way that they
rotate in opposite direction. One of these two gears is given rotary motion. The other gear
will also rotate meshing with the first one. The shaft on the driving gear will be extending
outside to get rotation from a prime mover. A little gap is left between the gears and the casing.
Method of working
The inlet of the pump is immersed in the reservoir. The prime mover actuates the
driving gear. This movement makes the other gear also to rotate. As these gears rotate, the
liquid is trapped between their teeth and the casing. The liquid is pumped out through the
outlet of the pump. A gear pump is illustrated in Fig. 6.6
Driving gear
Casing
Inlet
Outlet
Driven gear
Uses
Fig 6.6 Gear pump
Lubricating oil and liquids with high viscosity are pumped by pumps fitted with spur
gears. Pumps with helical gears are useful in pumping water and chemicals. Gear pumps can
handle pressures upto 140 k.g/cm2. The output can be 450 litres per min.
157
6.6.2 Vane pump
Construction
Vane pumps are equipped with a rotor. Radial slots are present on the rotor. Vanes
are attached to these slots and are designed to slide inside them. Rotor is placed inside the
casing. The casing and the rotor are placed eccentric. When the rotor is made to rotate,
vanes come out of the slots due to centrifugal force. Vanes rotate by touching the inner walls
of the casing. In some pumps, vanes are attached to the slots by means of springs to increase the pressure. A vane pump is illustrated in Fig. 6.7.
Method of working
The rotor is rotated by a prime mover. The liquid is trapped in between the vanes.
The design of the pump is such that the volume of the incoming liquid is increrasing and the
volume of the out going liquid is decreasing. So the liquid from the outlet is pumped with
increased pressure. Care is taken that the outlet volume of the liquid does not go back to the
inlet.
Casing
Vane
Rotor
Outlet
Inlet
Fig 6.7 Vane pump
A single layer vane pump can handle pressures from 17.5 to 70 k.g/cm 2 and a two
layer pump can handle upto 150 k.g/cm 2 of pressure.
158
6.6.3 Lobe pump
In a lobe pump, two lobes are
placed inside a casing and are made to
rotate to pump out liquids.
Outlet
The case of the pump is made of
cast iron. Both the lobes get rotational
power separately to rotate at same speed.
Both the shafts will be extending outside
to receive power. The are secured properly in the case with proper packing to
avoid leakage of oil.
The pump is provided with an inlet
and an outlet. The gap between the lobes
and the case is minimum and so the oil is
pumped through the gaps from the inlet to
the outlet.
Inlet
Fig 6.8 Lobe pump
A lobe pump is illustrated in Fig. 6.8.
6.6.4 Screw pump
Screws having helical grooves are used in this pump. When the screw starts rotating,
the oil is allowed through the helical grooves. The action of the pump is simple and smooth
and pumps out the liquid at high speed. They are used mostly in submarines.
6.7 Hydraulic motor
It is a device used to transform hydraulic energy into mechanical energy. Any
hydraulic motor can be used as an hydraulic pump. But a few types of pumps only can be
used as hydraulic motor.
The capacity of the hydraulic motor depends upon the quantity of the hydraulic
energy that it receives and its mechanical efficiency.
Hydraulic gear
The combination of hydraulic pump and hydraulic motor can be called as hydraulic
gear. It is equivalent to a gear box in a mechanical drive.
159
6.7.1 Types of hydraulic motor
The different types of hydraulic motors are
1. Rotary motor
2. Reciprocating motor
3. Constant speed motor
4. Variable speed motor
As in hydraulic pumps, there are different types of hydraulic motors like gear motor,
vane motor, radial reciprocating motor, linear reciprocating motor, etc.,
6.7.2 Hydraulic cylinder
A hydraulic cylinder converts hydraulic energy into linear mechanical energy. It is
also called as linear actuator. The piston placed inside a cylinder can be made to move to a
required distance at a required point of time by the liquid.
In order to maintain perfect alignment between piston and cylinder, a leak proof
arrangement of piston ring and packings (cup shaped packing & ‘V’ shaped packing) are
introduced between piston and the cylinder.
Cylinders are used to begin or stop any stroke movement or to clamp an object at a
particular position.
There are different types of hydraulic cylinders namely
1. Single acting cylinder
2. Double acting cylinder (with one piston rod)
3. Double acting cylinder (with two piston rods)
4. Ram type cylinder
5. Multi stage cylinder
6. Telescopic cylinder
7. Tandom or combination cylinder
In a single acting cylinder, the hydraulic liquid is allowed to pass through from only one
side as shown in the diagram. The piston moves to the other side because of the pressure
of the liquid.
On release of the pressure, the piston reaches its original position due to its own
weight or by a spring arrangement.
160
In double acting cylinders, the liquid is allowed from both the ends alternatively. So
the system is controlled effectively. There are two types in double acting cylinders - with
one piston rod & two piston rods. In the two piston rods double acting cylinder, the speeds
on both the directions are equal.
In a ram type cylinder, the piston and the piston rod is replaced by a ram of uniform
diameter. They are used in presswork of large capacity. A multi stage cylinder is a device in
which several cylinders are placed in linear arrangement.
Telescopic cylinders provide a compact arrangement when the cylinder needs to move
by a longer distance. Two or more cylinders are arranged one inside the other and the
central cylinder alone is provided with a piston. When objects of high mass are lifted for
greater heights, vehicles with fork lifts are used. Such devices are fitted with this type of
cylinders.
Fig. 6.9 shows different types of hydraulic cylinders.
Fig 6.9 Types of cylinders
A - Single acting cylinder
B - Double acting cylinder (with one piston rod)
C - Double acting cylinder (with two piston rods)
D - Ram type cylinder
161
6.8 Hydraulic valves
The efficiency of a hydraulic circuit depends upon the functioning of various control
devices used in the circuit. The control devices refer to the various types of hydraulic valves.
As the valves do the task of controlling the hydraulic energy, a hydraulic circuit without
valves is useless.
The following are the different types of valves used in hydraulic circuits.
A. Valves used to control the amount of flow in hydraulic circuits
a. Gate valve
b. Globe valve
c. Needle valve
d. Bye pass valve
e. Isolation valve
B. Direction control valves
a. Check valve
i) Swing valve
ii) Poppet valve
iii) Pilot valve
b. Two way plunger valve
c. Three way plunger valve
d. Four way plunger valve
C. Valve used to control the amount of flow in hydraulic equipment
a. Flow control valve (or) Flow regulator
D. Pressure reducing valve
E. Special valves
a. Sequence valve
b. Unloading vale
c. Counterbalance valve
d. Deceleration valve
162
6.8.1 Gate valve
Hydraulic liquid passes through various pipelines in a circuit. Gate valve is a device
useful in opening and closing of the passage for the liquid. A wedge shaped structure is
operated by a screw to open or close to control the flow of liquid.
When the passage is fully opened, very little resistance is offered to the flow of the
liquid. If the pressure of the liquid in the circuit is high, it is very difficult to operate the valve.
If the passage is opened partially, this valve functions normally. Gate valves are used
to cut off the flow of the liquid when maintenance works are carried out in the circuit.
6.8.2 Globe valve
Globe valve is used to open or close the flow of hydraulic liquid in the circuit like a
gate valve. A taper hole is present at the centre of the valve. A globe like part fits into the
hole. This part is operated to control the passage of the liquid.
This valve is operated even at high pressures. It is highly reliable when it is partially
opened. It is not generally used in hydraulic installations due to the fact that it is intended for
handling very high quantity of liquid.
6.8.3 Needle valve
The needle valve is similar to a globe valve. The sliding part of the valve looks like a
needle. It is suitable to be used in a hydraulic circuit since it is intended for handling smaller
quantities of liquid. It is also used where it is not necessary to change the flow very
frequently.
6.8.4 Byepass valve
Hydraulic liquid is pumped into the circuit by a pump. At some point of time, a part
of the pumped liquid or the whole of it may not be necessary to be passed into the circuit. A
byepass valve attached in the circuit to divert such quantity of the liquid back to the reservoir.
6.8.5 Isolation valve
In large hydraulic systems, the circuit may have many sub-circuits. When a repair or
maintenance work is to be done at any part of the circuit, the liquid supply to the particular
circuit should be stopped. An isolating valve is attached to each of the sub-circuit to cut it
off from the main circuit.
163
Direction control valves (Plunger valves)
Direction control valves are used to allow the hydraulic liquid into various parts of
the equipment and to reverse the direction of flow of the liquid. They are also known as
Plunger valve, Selector valve or Main valve. Different types of direction control valves are
A. According to the number of ports
a. Uni-directional plunger valve or Check valve
b. Two way plunger valve
c. Three way plunger valve
d. Four way plunger valve
B. According to the state of the valve in neutral position
a. Closed centre main valve
b. Open centre main valve
6.8.6 Uni-directional plunger valve
This valve is useful in allowing the flow of liquid in only one direction. It does not
allow the flow in the opposite direction. It is also known as plunger valve, check valve or
selector valve. A puppet type plunger valve is shown in Fig. 6.10. The valve now is in
closed condition. It is connected in line with the circuit.
Fig 6.10 Check valve (or) One way plunger valve
6.8.7 Two way plunger valve
In this valve, there are two ports - a. Inlet and b. Outlet. The moving part inside the
valve is known as spool or plunger. When the spool is positioned at the right side end, the
inlet and outlet are disconnected. If the spool is moved to the opposite side, both the inlet
and the outlet are connected and the flow of the liquid is established. An hydraulic device
like a hydraulic motor can be switched on or off by this valve. As there is no drain in this
valve to send back the liquid to the reservoir, it cannot be used to operate pistons in
cylinders. A two way plunger valve is shown in Fig. 6.11.
164
Fig 6.11 Two way plunger valve
A - Inlet
B - Outlet
6.8.8 Three way plunger valve
In this valve, there are three ports namely inlet, outlet and drain. Fig. 6.12 shows a
three way plunger valve. If the plunger is pushed to the right hand end, the inlet A and the
outlet B are conneced and the liquid is allowed into the circuit to operate the device. When
the plunger is pushed to the opposite end, the inlet A and the drain D are conneced and the
liquid is sent back to the reservoir. This type of valve is used to operate hydraulic motors
like single acting hydraulic cylinders.
Fig 6.12 Three way plunger valve
A - Inlet
B - Outlet
D - Drain
6.8.9 Four way plunger valve
There are four ports in this valve - i) Inlet A ii) Outlets B & C and iii) Drain D as
shown Fig. 6.13. When the plunger is pushed to a side, the inlet A and a outlet B are
connected to allow the liquid in a particular direction. In this position, the drain D is connected to the other outlet C. When the position of the plunger is altered, the inlet and the
outlet C are connected to allow the liquid in a different direction. Outlet B and drain D are
connected now. A four way plunger valve is used to operate a double acting hydraulic cylinder.
165
Fig 6.13 Four way plunger valve
A - Inlet
B & C - Outlets
D - Drain
6.8.10 Hydraulic lock
It is very important to ensure a correct clearance between the plunger and the
cylinder in plunger valves. It is difficult to keep a very little clearance between them. But at
the same time, more clearance will allow the liquid to pass through the clearance to the other
side. When the valves are handling pressures in the range of 140Kg/cm2, no problems arise.
But when pressure range reaches 210Kg/cm2, the system faces two difficulties.
1. Leakage and
2. Hydraulic lock
The plunger should have correct alignment with the cylinder moving concentrically
within it. But while handling higher pressures, the plunger loses the alignment and dash against
the walls of the cylinder to get stuck within it. Further movement of the plunger is prevented.
This effect is known as hydraulic lock. The lock can be released by reducing the pressure of
the system. The clearance between the plunger and the cylinder should be kept minimum
preferrably about 0.0025mm by finishing these surfaces by honing or by lapping.
6.8.11 Flow control valve (Flow regulator)
The speed of any hydraulic device (linear or rotary) depends upon the quantity of
flow of liquid. If the quantity of liquid pumped by the pump is increased, the speed of the
equipment also increases. If the speed of a particular equipment of a circuit is to be changed,
the quantity of the liquid is controlled by attaching a flow control valve. It is also known as
flow regulator.
6.8.12 Pressure reducing valve
A pressure relief valve is attached to a hydraulic circuit to control the pressure of the
liquid within the required limits. But a pressure reducing valve is used in specific sub-circuits
to further reduce the pressure in them.
166
Special valves
6.8.13 Sequence valve
When a series of operations are to be performed in a hydraulic equipment in a
specific order, a sequence valve is attached to the circuit. This will operate the devices in the
specific order. It is used in machines where production work is carried out.
For example, a work has to be held firmly before any machining is carried out on it.
The second operation cannot be done before the first is performed. So, a sequence valve is
very important in executing the operations in a specific sequence.
6.8.14 Unloading valve
This valve is used where it is necessary to provide the equipment with different speeds
one by one. The different speeds shall be used alternately as in the case of a hydraulic shaper.
6.8.15 Deceleration valve
The speed of a hydraulic actuator is made to get slower on reaching a specific point.
The first phase moves at relatively faster speed. The valve used to reduce the speed at a
particular point is known as deceleration valve.
6.9 Hydraulic circuit for a shaping machine
The important elements of a hydraulic shaper are
1. Constant discharge hydraulic pump
2. Pressure relief valve
3. Four way control valve
4. Cylinder with piston
Hydraulic liquid is pumped by a constant discharge pump into the direction control
valve. It has four ports and three stages. If the pressure goes beyond desired limits, the
same is released by the pressure relief valve.
The liquid reaches the right side of the cylinder through the inlet E and outlet A of the
valve. Due to the pressure of the liquid, the piston moves towards left. The toolhead moves
forward to perform the forward cutting stroke. The liquid on the left side of the piston is sent
back to the reservoir through B and P.
Due to the change of position of plunger inside the valve, the liquid reaches the left
side of the cylinder through the inlet E and outlet B. Piston moves towards right. The toolhead
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moves in the opposite direction and this movement is known as the return stroke. The liquid
on the right side of the piston is sent back to the reservoir through A and P.
Ram
Cylinder
Piston
Direction
control valve
Relief valve
Pump
Reservoir
Fig 6.14 Hydraulic circuit of a shaping machine
Quick return of the ram
Due to the change of stroke volume of the cylinder during forward and return stroke,
the piston returns at a faster rate.
The stroke volume of the cylinder during return stroke is comparitively smaller than
during forward stroke due to the presence of the piston rod. So, the pressure increases
automatically to push the piston and the toolhead at a faster speed during return stroke.
168
6.10 Hydraulic symbols
Sl.No
Description
Symbol
1.
Liquid flow line
2.
Drain line
3.
Line crossing
4.
Line joining
5.
Flexible line
6.
Direction of flow
7.
Line to reservoir - above liquid
8.
Line to reservoir - below liquid
9.
Fixed displacement pump
10.
Variable displacement pump
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6.10 Hydraulic symbols (contd.)
Sl.No
Description
Symbol
11.
Electric motor
12.
Open valve
13.
Closed valve
14.
Check valve
15.
Pressure reducing valve
16.
Pressure gauge
17.
Filter
18.
Single acting cylinder
19.
Double acting cylinder- 1 piston rod
20.
Double acting cylinder- 2 piston rods
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QUESTIONS
I A. Choose the correct option
1. The pressure obtained by a gear pump is
a. 180 k.g/cm 2
c. 170 k.g/cm 2
b. 140 k.g/cm2
d. 150 k.g/cm2
2. A centrifugal pump is classified according to the type of casing as
a. Low lift pump
c. Mixed flow type
b. Closed impeller pump
d. Diffuser casing pump
3. Impeller is a part found in a
a. reciprocating pump
c. centrifugal pump
b. gear pump
d. vane pump
4. A cylinder used in lifting of objects of high mass is
a. single acting cylinder
c. telescopic cylinder
b. double acting cylinder
d. combination cylinder
I.B. Answer the following questions in one or two words
1. How are hydraulic pumps classified according to the volume of the outlet?
2. Mention one property of a positive displacement pump.
3. Which type of pump is a vane pump?
4. Mention a type of a special valve.
5. What do you know about the suction head of a centrifugal pump?
6. Which type of a pump has a connecting rod?
7. How is a hydraulic cylinder otherwise known as?
II. Answer the following questions in one or two sentences.
1. What is hydraulics?
2. Define a hydraulic pump.?
3. What is the principle of a hydraulic pump?
4. Mention the types of hydraulic pumps.
5. What is a hydraulic motor?
6. What are the important parts of a centrifugal pump?
7. What are the uses of a reciprocating pump?
8. What is a hydraulic cylinder?
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9. What are the uses of a hydraulic cylinder?
10. What are the valves used to control the flow of hydraulic liquid?
III .Answer the following questions in about a page
1. List out the differences between a centrifugal pump and a reciprocating pump.
2. Explain the parts of a centrifugal pump with a diagram.
3. Explain the parts of a reciprocating pump with a diagram.
4. Explain a lobe pump with a diagram.
5. Draw the circuit of a hydraulic shaper and label its parts.
172
7. ELECTRICAL EQUIPMENTS
7.1 Introduction
Electricity is a form of energy. It occupies an important place in our daily activities –
in life and business. One cannot see electricity but can feel the effects of it. One should not
have a direct contact with it as it may cause damages.
Electricity is being used for everything - from providing light and other facilities to our
household to latest space research. The contributions made by American scientists like
Benjamin Franklin, Thomas Alwa Edison and Michael Faraday of England are immeasurable.
7.2 Motor
A motor is a device used to convert electrical energy into mechanical energy. Different types of motors are used according to their usage and the place in which they are used.
7.2.1 Types of motors
1) D.C. Motor
2) A.C. Motor
i) Three phase induction motor
a) Squirrel cage induction motor
b) Slip ring induction motor
ii) Single phase induction motor
a) Split phase induction motor
b) Capacitor induction motor
c) Repulsion motor
d) Shaded pole motor
7.2.2 Three phase induction motors - the principle of working
When a three phase supply is supplied to three phase windings placed 120° apart
inside the stator of an induction motor, a constant rotating magnetic field is induced.
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It induces e.m.f in the conductors of the rotor known as armature. According to
Lens’ law, we know that when an e.m.f. is induced in a circuit electromagnetically, the
current set up always opposes the motion or change in the current which produces it.
7.3 Construction of a induction motor
The main parts of a induction motor are
1. Stator
2. Rotor
7.3.1 Stator
It is made of thin sheets arranged as tube. The laminated core has slots cut
longitudinally on it parallel to the axis. It is wound for two, four, six poles depending on the
required speed.
Eye-hole
Frame
Stator core
Stator slot
Spider
Leg
Fig 7.1 Stator
7.3.2 Rotor
Based on the construction of the rotor, the three phase induction motor can be
classified as
1. Squirrel cage induction motor
2. Slip ring induction motor
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7.3.3 Construction of a squirrel cage induction motor
The rotor of a squirrel cage motor is made of cylindrical laminated core with small
openings. These openings receive insulated conductors. The openings are formed parallel to
the axis. So, the motor starts to run with a uniform rotating torque. Humming is reduced to a
great extent. One bar is placed in each slot and all the bars are short circuited by two end
rings. This makes a complete squirrel cage rotor.
Conductors
Rotor shaft
Short circuiting ring
Bearing
Fig 7.2 Rotor of squirrel cage induction motor
There are two types of squirrel cage induction rotors
1. Single squirrel cage induction rotors - It has only one winding in the rotor.
2. Double squirrel cage induction rotors - It has two windings in the rotor.
7.3.4 Construction of a slip ring induction motor
The rotor of the slip ring motor is actually wound for three phase windings connected
in star formation. These windings are placed in insulated rotor slots and the ends are brought
out and connected to the three slip rings mounted on the shaft. Brushes mounted on the slip
rings connect the rotor windings to external resistance for the purpose of starting.
This motor is started with full additional resistance in the rotor circuit to ensure less
starting current and more starting torque. The external resistance is reduced gradually and
the required speed is obtained by short-circuiting the three slip rings. The rotor winding will
have the same number of poles found in the stator. This motor is also known as wound rotor
induction motor.
175
7.3.5 Differences between a squirrel cage induction motor and
a slip-ring induction motor.
Slip ring induction motor
Squirrel cage induction motor
1. Simple in construction
1. Construction is complicated because
rotor is also wound with insulated wire
2. Low cost
2. The cost is high
3. Operates at high efficiency
3. Efficiency is not high
4. There is no chance of sparks and
hence it is explosion proof
4. Sparking risk is there because of
slip-rings and the brushes riding on them
5. Requires the least maintenance
5. Maintenance is troublesome
6. Starting arrangements are simple
6. Requires costly starters
7. Starting torque is less
7. High starting torque
8. Speed control is not easily possible
8. Speed can be changd earily
7.4 A.C single phase capacitor start motor
The stator of a A.C single phase capacitor start motor has two windings - running
winding & starting winding. A capacitor and a centrifugal switch are connected in series with
the starting winding. A squirrel cage rotor is fitted in this motor. Capacitor creates 90°
phase difference between the two windings.
Single phase current is supplied and the development of rotating magnetic field makes
the rotor to rotate. When the rotor attains 70% of the total speed, the centrifugal switch
disconnects the starting winding. This motor has high starting torque. The direction of
rotation can be changed by just changing the connection of terminals of any one of the
windings. The motors find extensive use in wet grinders, small grinding machines, drilling
machines, compressor motors used for air -conditioners and refrigerators.
176
Capacitor
Running
winding
Rotor
Centrifugal
switch
Starter winding
Fig 7.3 A.C. Single phase capacitor start motor
7.5 Starters for induction motors
7.5.1 Need of starters
When induction motors are directly switched on to supply, it takes about five to six
times of full load current. This initial excessive current causes damages to the motor and
supply wires. Starters are used to limit the inrush of starting line current and full current is
supplied when the motor picks up speed. It consists of protective elements like no volt coil
and over load relays.
7.5.2 Different types of starters for induction motors
There are different types of starters used for induction motor.
i) Direct – on – line starter (D.O.L Starter)
ii) Star – delta starter
iii) Auto transformer starter
iv) Rotor resistance starter (for slip ring motor)
7.5.3 Direct - on - line (D-O-L) starter
It is simple in construction when compared with other starters. It permits the motor
to startup with full voltage on. It has protective elements to safeguard the motors against
over loading and single phasing. Single-phasing means operation of motor with one line cut
of accidentally. When the start button is pressed, the no volt coil circuit energises. The
contacts are pressed against spring tension to connect the motor terminals to three-phase
supply. The motor starts running.
177
Plunger
Bimetallic strip
Fig 7.4 D.O.L starter
Even if the pressing of ‘start’ button is stopped, the circuit is closed through the
fourth conductor and the motor continues to run. When the motor is overloaded, the
temperature of the heating elements becomes high to heat the bimetallic strip. This makes
over load relay (OLR) to press a lever to open the no volt coil for a moment to switch off the
supply to stop the motor.
If the OFF button is pressed, the supply to the No volt coil is disconnected and the
motor is stopped. Direct-on-line starters are used for motors with capacity upto 5 hp.
7.5.4 Star – delta starter
This starter has two positions – ‘start’ and ‘run’. When the handle is pressed to
‘start’, the three motor windings are connected in star formation. Each phase winding gets
only 58% of the line voltage. So the starting line current to the motor is reduced. As the
motor picks up speed and attains nearly 80% of normal r.p.m., the starter handle is pushed
to ‘run’ position. In this run position, the three winding get connected in delta formation so
that each winding gets full supply voltage and full line current.
This starter is provided with usual protective devices such as overload relay, no volt
release and single phase preventer. Star-delta starter is used for motors of capacity 5 hp to
15 hp.
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Fig 7.5 Star - Delta starter
7.5.5 Auto transformer starter
An auto transformer is fitted in this starter and so it is costlier. Star connected
transformers with 40, 60 and 80% tapings, allows specific voltage to be pressed against the
motor windings.
When the starter handle is thrown to start position-reduced voltage is supplied to the
motor windings and the motor starts with reduced line current and reduced torque. When
the starter handle is pushed to run position, full line voltage is applied to motor windings and
the auto transformer is isolated from the circuit. This starter is provided with usual protective devices such as overload relay and no volt coil. This type of starter is intended for
starting three phase induction motors of capacity more than 15 hp.
179
7.5.6 Rotor resistance starter
Slip ring motors are always started with a resistance in series with each rotor phase.
In this starter, full line voltage is applied across starter windings. Full value additional
resistance is added in series with each phase of the rotor windings. These resistances are
immersed in oil. As the rotor starts up, the handle is rotated slowly until the entire resistance
is out. The motor then runs normally. At this stage, rotor windings are short-circuited
eliminating the resistance. Now the motor runs like a squirrel cage motor
QUESTIONS
I. A Choose the correct option
1. The device used to converet electrical energy into mechanical energy is
a. generator b. electric motor
c. starter
d. transformer
2. Starter used for motors of capacity upto 5 hp is
a. star – delta starter
b. Direct – on – line starter
c. auto transformer starter
d. rotor resistance starter
3. The safety device used to protect the motor from over load or single phasing is
a. no volt coil b. over load relay
c. contactor d. capacitor
I. B Answer the following questions in one or two words
1. Expand - D.O.L starter.
2. Name the windings present in the A.C. single phase capacitor start motor.
3. Expand - A.C.
II. Answer the following questions in one or two sentences
1. List out the types electrical motors.
2. What are the types of starters used in induction motors?
3. What are the safety devices fitted in starters to protect the induction motors?
4. What is the need of a starter in a motor?
III. Answer the following questions in about a page
1. Differenciate a squirrel cage induction motor from a slip ring induction motor.
2. Draw and explain a D.O.L starter.
3. Draw a neat diagram of a star - delta starter and explain.
4. Draw and explain a A.C. single phase capacitor start motor.
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8. WELDING
8.1 Introduction
Welding can be defined as the process of joining two metal parts by applying heat .
In industry, welding process is primarily used for fabricating works.
Welding is useful in making permanent joints. It can be performed by applying or not
applying pressure. The contours of the metal parts are molten to make the joint in some
methods. In some types of welding processes, filler metal is used. In some other methods,
filler metal is not used.
The process of welding finds application in manufacturing automobiles, aeroplanes,
rail coaches, machine components, metal structures, boilers and ships. Generally, welding
process is applied wherever metal works are performed.
8.2 Methods of welding
There are two methods by which welding is performed
1. Plastic welding
2. Fusion welding
8.2.1 Plastic welding
In this method, the metal parts are heated to plastic state. At this stage, pressure is
applied to make a perfect joint. It is also known as pressure welding.
8.2.2 Fusion welding
The metal parts are heated upto the point of melting in this method. The joint is made
at this stage and the parts are allowed to cool. On cooling, the molten metal forms a solid
joint. No pressure is applied in this method. Hence, it is also known as prersure less
welding. Arc welding and gas welding fall in this category.
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8.3 Classification of welding processes
1. Arc welding
a. Carbon arc welding
b. Metal inert gas welding
c. Tungsten inert gas welding
d. Atomic hydrogen welding
e. Plasma arc welding
f. Submerged arc welding
g. Electro slag welding
2. Gas welding
a. Oxy-acetylene welding
b. Air-acetylene welding
c. Oxy hydrogen welding
3. Resistance welding
a. Butt welding
b. Spot welding
c. Seam welding
d. Projection welding
e. Percussion welding
4. Thermit welding
5. Solid state welding
a. Friction welding
b. Explosive welding
c. Ultrasonic welding
d. Diffusion welding
6. Newer welding
a. Electron beam welding
b. Laser welding
7. Welding related processes
a. Oxy-acetylene cutting
b. Arc cutting
c. Hard facing
d. Brazing
e. Soldering
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8.4 Arc welding
In arc welding, the edges of two metal parts are melted by an electric arc and the
joint is made. An electrode made of a suitable metal is utilised for this purpose. The
electrode is taken closer to the parts to be joined and electric current is supplied to both the
parts and the electrode. An electric arc is made between the electrode and the metal parts.
This arc generates high temperature and melts the metal parts. The parts are joined at this
molten state. The filler metal in the form of electrode is deposited along the joint. The metal
parts are joined without the application of any pressure. Electrical energy is coverted into
heat energy in arc welding.
The distance between the metal parts and the eleclrode should be around 3mm. The
heat generated during arc welding ranges from 5000°C to 6000°C. A generator or a
transformer supplies the required current to both the electrode and the metal parts. The
electrodes are flux coated to prevent the molten metal from reacting with the atmosphere.
Fig. 8.1 shows arc welding operation.
Flux coating
Electrode
Arc stream
Gaseous shield
Slack
Weld deposit
Depth of fusion
Fig 8.1 Arc welding
183
8.5 Arc welding equipments
The following equipments are used for the process of arc welding
1. D.C welding generator (or) AC transformer
2. Cables
a. Electrode cable
b. Work cable
3. Electrode holder
4. Electrode
5. Gloves
6. Protective shield (or) Goggles
7. Apron for the operator
8. Wire brush
9. Chipping hammer
A typical arc welding circuit is shown in Fig. 8.2
Electrode
Power source
Electrode
holder
Work
Fig 8.2 Arc welding circuit
184
8.5.1 Differences between DC welding generator and AC welding
transformer
DC welding generator
AC welding fransformer
1. Low efficiency
1. The efficiency is high
2. High power cost
2. The cost for the power is low
3. The cost of the machine (equipment) is
high
3. Low machine cost
4. Runs on low voltage
4. High voltage is necessary
5. Safe equipment
5. The chances of accidents is high
6. Uncoated electrodes may be used
6. Only flux coated electrodes are used
7. Joints are made with ferrous and nonferrous metal parts
7. Non-ferrous metal parts cannot be
joined
8. Work is connected to the positive
terminal (+) and the electrode is
connected to the negative terminal (-)
8. No restriction in the direction of power
supply connection
9. Noisy functioning
9. No noise during operation
10. Easy maintenance of equipments
10. Requires proper maintenance
11. The cost of the process is low
11. High process cost
12. Thin metal parts can easily be welded
12. Difficult to weld thin parts
8.5.2 Specification of electrodes
Generally, the size of the electrodes is specified by the length and its diameter. They are
available to a maximum of 12 mm diameter and 450 mm length. The size of the electrode
increases with the current used. In manual welding, the size of the electrode changes according
to the thickness of the metal parts. Spring like electrodes are used in automatic welding.
8.5.3 Types of electrodes
The electrodes used in arc welding are of two types
1. Consumable electrode
2. Non-consumable electrode
185
There are three types of consumable electrodes. They are
1. Bare electrodes
2. Lightly coated electrodes
3. Heavily coated electrodes
Non-consumable electrodes are used in the processes of atomic hydrogen welding
and TIG welding.
8.5.4 Selection of electrodes
The material used for manufacturing electrodes depends upon the material to be
welded. Given is the list indicating suitable materials for manufacturing electrodes for
welding different metals.
Sl. No.
Material to be welded
Electrode material
1.
Wrought iron
Low carbon steel
2.
Mild steel
Mild steel with copper coating
3.
Alloy steel
Nickel steel
4.
Cast iron
Cast iron
5.
Aluminium
Cast aluminium alloy
6.
Carbon steel
Steel wire(0.15% carbon & 0.025% Phosperous
7.
Copper
Copper
8.
Brass
Brass
8.6 Carbon arc welding
In carbon arc welding, the process of welding is carried out by an electric arc. The
arc formed between the electrode and the workpiece generates high amount of heat. In
D.C. electric supply, the carbon electrode is connected to the negative terminal and the
positive terminal is connected to the workpiece. During the formation of the electric arc, the
temperature of the positive terminal is 4000°C and the negative terminal will be around
3000°C. Carbon, the electrode material will not fuse with the workpiece materials. This
prevents the joint from becoming weak. A lengthy arc produces Carbon-monoxide at the
location of welding and prevents the molten metal from reacting with the atmospheric air.
Fig. 8.3 illustrates the process of carbon arc welding.
186
Carbon electrode
Work
Fig 8.3 Carbon arc welding
Both ferrous and non-ferrous metals can be welded by this method. Steel sheets,
copper and its alloys, brass and aluminium parts are welded using carbon arc welding. This
method of welding can also be done automatically. Starting of the electric arc is easy and the
temperature is controlled easily. The disadvantage of this method is the presence of blow
holes in the joint.
8.7 Gas welding
Gas welding is the process of melting and joining metal parts by means of a gas flame.
Generally pressure is not applied during the process of gas welding. Oxygen and acetylene
gases are made to pass through the welding torch. These gases are mixed at the required
ratio at the torch and the tip of the welding torch is ignited to produce the flame. Because of
the heat generated by the flame, the edges of the metal parts are melted. Filler rod provides
the additional metal required for making the joint. The flux coated on the electrodes prevents
oxidation and removes impurities. This method is suitable in welding metal parts of thickness
varying from 2mm to 50 mm. The temperature of the flame is around 3200°C.
8.8 Gas welding equipments
The following equipments are necessary for gas welding
1. Gas cylinders
2. Regulators
187
3. Pressure gauges
4. Rubber hoses
5. Welding torch
6. Safety goggles
7. Gloves
8. Spark lighter
9. Wire brush
8.8.1 Gas cylinders
Oxygen and acetylene gases are stored in separate cylinders and used for gas
welding. The colour of oxygen cylinder is black and the acetylene gas is stored in maroon
cylinders. Oxygen is stored at a pressure of 125Kg/cm 2. Acetylene gas is stored at a
pressure of 16 Kg/cm2. in the cylinder.
Pressure
gauges
Hoses
Control valves
Torch
Nozzle
Oxygen
cylinder
Acetylene cylinder
Fig 8.4 Gas welding
8.8.2 Regulators
Separate regulators are fitted on both the cylinders. A regulator is used to control the
working pressure of the gases. The working pressures of oxygen is 1Kg/cm 2 and acetylene
is 0.15Kg/cm 2. Working pressure of these gases are altered according to the thickness of
the metal parts of the joint.
188
8.8.3 Pressure gauges
Two pressure gauges are fitted each on the oxygen cylinder and on the acetylene
cylinder. One of the pressure gauges indicates the pressure of the cylinder and the other
gauge indicates the working pressure of the specific gas.
8.8.4 Hoses
Separate hoses are used to connect the two cylinders with the welding torch through
regulators. The colour of the hose from the oxygen cylinder is black and the one from the
acetylene cylinder is red. These hoses carry the gases to the welding torch.
Gas welding kit is shown in Fig. 8.4
8.8.5 Welding torch
Oxygen and acetylene reach the welding torch through the passages of hoses from
the respective cylinders. These gases are mixed in the mixing chamber of the welding torch.
Flame is produced at the tip of the torch when the gases are ignited. There are two control
valves present in the torch to control the quantity of oxygen and acetylene. By this control,
the grade of the flame can be altered. The size of the flame is altered to suit the thickness of
the metal parts. A welding torch is shown in Fig. 8.5
Mixing chamber
Nozzle
Oxygen passage
Oxygen control
valve
Hoses
Acetylene
passage
Acetylene
control valve
Fig 8.5 Welding torch
8.8.6 Goggles
Oxy acetylene flame emits ultraviolet and infrared rays. These rays are highly harmful
to bare eyes. In order to protect the eyes of the welder, goggles should be used by him.
189
8.8.7 Welding gloves
Protective hand gloves are used by the operator to prevent possible damages that
may be caused by high temperatures and metal splashes during welding.
8.9.8 Spark lighter
Spark lighter is used to ignite the oxy-acetylene gas at the tip of the welding torch.
8.8.9 Wire brush
Wire brushes are useful in cleaning the weld before and after the welding process.
8.9 Types of gas flames
The size of the flame can be altered by varying the ratio of oxygen and acetylene. By
doing so, the following three types of flames are obtained.
1. Neutral flame
2. Carburising flame
3. Oxidising flame
8.9.1 Neutral flame
The supply of equal quantities of oxygen and acetylene produces neutral flame.
There are two zones in this flame- 1. Sharp and bright inner cone and 2. Bluish outer cone.
The temperature of the inner cone will be around 3200°C. This neutral flame is generally
used as it will not cause any chemical reaction upon the heated metal.
8.9.2 Carburising flame
This flame is also known as reducing flame. The supply of acetylene will be more
than oxygen to produce this flame. Carburising flame consists of three zones namely,
1. Sharp inner cone
2. White intermediate cone
3. Bluish outer cone
Carburising flame is useful in welding low carbon steel and alloy steels. It is also
used to harden the outer surface of metal parts.
The types of gas flames are shown in Fig. 8.6
190
Neutral flame
Carburising flame
Oxidising flame
Fig 8.6 Types of flames
8.9.3 Oxidising flame
Oxidising flame is obtained by supplying more oxygen than acetylene. It consists of
two zones namely bright inner cone and outer cone. This flame is useful in welding brass and
bronze.
8.10 Filler rods used in gas welding
Filler rods used in gas welding supply the additional metal in making joints. These
rods are melted by the gas flame and deposited over the parts of the joint. Generally the
filler rods are made of the same metal as that of the parts of the joint.
The diameter of the filler rod depends upon the thickness of the parts to be welded.
The strength of the welding joint is increased by adding Nickel or Chromium in filler rods. A
thin coat of copper is provided on the filler rods to prevent the molten metal from reacting
with atmospheric oxygen. Flux may be applied either in powdered form or liquid form.
191
8.11 Advantages of gas welding
1. Applied for different classes of work
2. Welding temperature is controlled easily
3. The quantity of filler metal added in the joint can easily be controlled
4. The cost of the welding unit is less
5. The cost of maintenance is less
6. Both welding and cutting can be done
8.12 Limitations of gas welding
1. Intended for welding thin workpieces only
2. The process of welding is slow
3. The time taken by the gas flame to heat the metal is more when compared with
electric arc
4. The strength of the joint is less
5. Great care should be taken in handling and storing gas cylinders
8.13 Differences between arc welding and gas welding
Arc welding
Gas welding
1. The heat is generated by the electric
arc
1. The required heat is provided by the
gas flame
2. The working temperature is about
4000°C
2. The temperature of the gas flame is
about 3200°C
3. The filler rod is used as electrode.
3. Filler rod is used separately
4. Care should be taken aginst the
dangers that may be caused because of
electricity
4. The danger of the process is because of
the gases at high pressure
5. The strength of the joint is more
5. The joint is not as strong as that of arc
welding
6. Brazing and soldering cannot be
performed by the electric arc
6. The processes of brazing and soldering
can be done with the gas flame
7. The filler rod metal should be selected
as the same metal as that of the parts of
the joint.
7. The filler rod metal can be different
from that of the parts of the joint.
192
8.14 Resistance welding
The process of resistance welding involves
(i) developing electrical resistance in the parts of the joint to bring them into a plastic
state and
(ii) applying pressure on the parts to make the joint
Pressure
Movable
arm
Transformer
Work
Copper
electrodes
Fixed arm
A.C
Frame
Fig 8.7 Resistance welding
Two copper electrodes are connected to an electric circuit of low resistance. The
parts to be welded are placed between the electrodes. When current is allowed to pass
through the electrodes, high electrical resistance is developed at the joint. Because of the
resistance, heat is generated at the joint. The metal parts reach plastic state at this high
temperature.
At this point, pressure is applied by means of either mechanical or hydrulic or
pneumatic power source to make the joint. Current is provided by a suitable A.C.
transformer. Resistance welding is useful in welding sheet metal, bars and pipes.
Fig. 8.7 shows resistance welding.
193
8.15 Welding related processes
Following are some important welding related processes used in industries.
1. Oxy-acetylene cutting
2. Arc cutting
3. Hard facing
4. Soldering
5. Brazing
8.15.1 Oxy-acetylene cutting
Plates made of iron and steel are cut by oxygen, acetylene cutting torch. Oxygen and
acetylene are mixed in the cutting torch and a gas flame is generated. The flame heats the
sheets to bring them to red hot condition. High pressure oxygen is supplied on the red hot
metal through a separate central hole of the cutting torch. Iron and steel sheets are thus cut
by the jet of oxygen. Fig. 8.8 shows oxy-acetylene cutting.
Oxygen
Mixed gases
Preheat
orifices
Oxygen orifice
Fig 8.8 Oxy-acetylene cutting
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8.15.2 Arc cutting
In this process, the metal parts are heated by means of carbon or metal electrodes.
High pressure air is supplied on the molten metal to remove it and cut the metal parts.
Oxygen jet is supplied along with the electrode instead of air nowadays. Arc cutting is not
suitable for accurate work.
8.15.3 Hard facing
Hard facing is a process of coating a hard matrial on soft metal parts. Powdered
coating metal is filled in the welding gun. The metal powder is melted by the oxy-acetylene
gas flame. The supply of inert gas at pressure makes the powdered metal to split into small
particles. These particles are sprayed on the surfaces of the soft metal. Coatings of Tungsten
carbide, Chromium carbide and Aluminium oxide can be made on the surfaces of different
cutting tools and cutters. Fig. 8.9 shows hard facing.
Powdered
metal
Work surface
Coating
Burning gases
Inert gas
Oxy-acetylene
gas
Atomized spray
Fig 8.9 Hard facing
8.15.4 Soldering
Two parts made of similar or dissimilar metals are joined by a solder made of a
fusible alloy. Solder is an alloy made of Tin and Lead. The melting temperature of the solder
is in the range of 150°C to 350°C. The surfaces of the two metal parts are cleaned and held
in correct positions. Flux paste made of Zinc chloride is applied on the parts by soldering
iron. Application of flux prevents oxidation. The solder is melted by the heat provided by the
soldering iron and filled between the metal parts. The solder solidifies and joins the metal
parts. Soldering is illustrated in Fig. 8.10.
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Solder
Soldering iron
Work
Soldering joint
Fig 8.10 Soldering
8.15.5 Brazing
In brazing, filler metal in molten state is filled between the metal parts of the joint.
The filler rod is heated upto 450°C. The parts to be joined are cleaned and the molten filler
metal is applied between the parts to make the joint. In this method, the metal parts are not
melted. The process of brazing is illustrated in Fig. 8.11.
Work
Brazing torch
Brazing tip
Filler rod
Fig 8.11 Brazing
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8.16 Types welded joints
Following are the types of welded joints
1. Butt joint
2. Lap joint
3. T-Joint
4. Corner joint
5. Flange joint
8.16.1 Butt joint
Butt joint is a joint in which the corners or the edges of two metal parts are joined.
The process is done by keeping the metal parts on a same plane. The edges of metal parts of
thickness upto 5 mm may be kept open square. If the thickness of the metal parts exceeds
5 mm, edges of the parts need to be prepared in proper shape before welding. D i f f e r e n t
types of welded joints are shown in Fig.8.12
Butt joint
‘T’ joint
Lap joint
Corner joint
Flange joint
Fig 8.12 Types of welded joints
8.16.2 Lap joint
It is a joint in which the metal plates are placed overlapping before welding. The
edge of one part is welded with the surface of the other plate. There are two types of lap
joint namely (i) Single lap joint and (ii) double lap joint.
8.16.3 T-joint
This joint is made by keeping the metal plates at perpendicular (90°) to each other.
Sheets with thickners over 3 mm only are welded by this type
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8.16.4 Corner joint
Two metal sheets kept at 90° to each other are welded by this joint. This method is
adopted when making boxes and tanks. Corner joints are adopted for thin and thick sheets.
8.16.5 Flange joint
The plates of the joint may be kept parallel or at 90° to each other. The edges of the
plates are bent to form the shape of a flange.
8.17 Safety precautions for welding
We make use of electrical devices and inflammable gases like oxygen and acetylene
in welding. If proper care is not shown in handling them, there is always a possibility of
accidents taking place. So,welding process should be carricd out with due safety and
caution.
8.17.1 Safety precautions to be observed during gas welding
1. Gas cylinders should be kept in ventilated locations.
2. Cylinders should not be kept near hot locations. They should be kept away from
electrical terminals.
3. Pressure regulators should be closed after the welding work is completed.
4. Regulators should be handled properly.
5. Old and worn out regulators should be replaced immediately.
6. The operator should wear goggles, gloves, apron and proper footwear.
7. Fire extinguishers and First-aid box should be kept ready always.
8.17.2 Safety precautions to be observed during arc welding
1. The welder should always wear goggles. gloves, apron and proper footwear
during welding.
2. Welding shop should be located properly so that it does not cause any discomfort
to others.
3. The welder should act carefully against electric shocks.
4. A high quality electrode holder should be put into use.
5. Power supply should be provided at required voltage and uniform current.
6. Fire extinguishers and First-aid box should always be kept ready in a welding
shop.
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QUESTIONS
I A. Choose the correct option
1. Atomic hydrogen welding is a ------------ process
a. gas welding
b. resistance welding
c. arc welding
d. solid state welding
2. The working temperature of arc welding is
a. 100°C-150°C
b. 50°C-100°C
c. 5000°C-6000°C
d. 150°C-200°C
3. The pressure of oxygen in the cylinder of gas welding equipment is
a.16 kg/cm 2
b. 125kg/cm2
c. 100kg/cm 2
d. 14kg/cm2
4. The presssure of acetylene in the cylinder of gas welding equipment is
a. 16kg/cm 2
b. 125kg/cm2
c. 100kg/cm 2
d. 14kg/cm2
I.B. Answer the following questions in one or two words
1.Name the flame obtained by supplying more acetylene than oxygen.
2. Which is otherwise known as plastic welding?
3. Which type of welding converts electrical energy into heart?
4. Which type of welding require filler rods?
5. Name the colour of the hose which connects the oxygen cylinder with the welding
torch in gas welding.
6. Name the colour of the hose which connects the acetylene cylinder with welding
torch.
II. Answer the follwing questions in one or two sentences
1. How is welding done?
2. What are the methods of welding?
3. How is the welding electrodes specified?
4. What are the types of electrodes?
5. Name the three types of flames generated in gas welding?
6. Write short notes on filler rods used in gas welding?
7. Write any four advantages of gas welding?
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8. What are the limitations of gas welding?
9. What are the types of welded joints?
III. Answer the following questions in about a page
1. List out the types of welding.
2. Discribe arc welding with a diagram.
3. Name and explain the equipments required for arc welding.
4. List out different electrode metals for welding parts of different metals.
5. Explain any two types of flames obtained in gas welding with diagrams.
6. What are the differences between arc welding and gas welding
7. List out the safety precautions to be observed during arc welding and gas welding.
IV. Answer the following questions in detail
1. Explain carbon arc welding with a diagram.
2. What are the differences between DC arc welding generator and AC arc
welding transformer?
3. Explain any five equipmants used in gas welding.
4. Explain gas welding with a diagranm.
5. Explain resistance welding with a diagram.
6. Explain any four welding related processes with diagrams.
7. Explain any four welded joints with diagrams.
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9. CNC MACHINES
9.1. Introduction
Production is a process of converting raw material into finished products. The
process of production is achieved by the collective efforts of man and machine using
materials and tools. It requires information and energy to accomplish production by
machining. Over the period of time, several techniques and methods are used in the process.
The evolution of new methods of production saw the increasing involvement of machines in
providing the information and energy required for production and the role played by the
humans declined. Prepared programs consisting of informations and instructions took the
role of controlling the machines instead of manual control. This has led to a manufacturing
system of higher production at lower cost with more accuracy.
9.2. Numerical Control
In NC System, intervention of human beings in the machining process is substituted
by some operating instructions in a coded form. This coding otherwise known as part
program is stored in cards or tapes. Getting the required instructions from these input
media, the machine carries out different tasks in a proper sequence.
Numerical control can be defined as a system in which actions of a machine tool are
controlled by recorded informations in the form of numerical data.
Computer Numerical Control
When the activities of a Numerical Control machine is administered by a dedicated
computer, it is known as Computer Numerical Control machine tool. The functions of the
machine tool are controlled by the instructions stored as programs in the computer.
9.3
Elements of NC machines
As explained in the previous section, the NC system requires the preparation of
manuscript (part program) based on the product drawing, preparation of input media (punched
cards & punched tapes), the data entry into the control unit, consequent processing and
actuation of the machine tool to produce the desired part.
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Fig 9.1 Lay-out of a NC System
In performing all the above operations, the NC machine may have the following elements:
1. Software
2. Machine Control Unit
3. Driving devices
4. Manual control unit
5. Machine tool
9.3.1 Software
A series of instructions are required to control the actions of a NC machine. These
instructions are prepared based on the profile and the material of the part being
manufactured. These instructions and their storage media can be called as software.
Software of a NC system can be referred to as items comprising of instructions
(programs), languages used to write these programs and a variety of input media.
The instructions given to the NC machine may be dimensional or managerial. They
are fed into the control unit as different numbers only. The decimal system of numbering uses
10 digits (0 to 9) to represent any number. The base of the numbers will be 10. But in order
to provide informations into the control unit or a computer, a convenient system of numbering known as binary format is used. In this system, only two digits (0 & 1) are used and the
base is 2. All instructions and informations are converted as numbers consisting of digits 0
and 1. It becomes easy to record the informations on punched tapes or punched cards in the
form of holes (Holes may indicate 1 and no hole may represent 0)
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Input media
Different types of input media are used to store informations and to provide input to
various control units of the NC machine. They are
1. Punched cards
2. Punched tapes
3. Magnetic tapes
4. Floppy disks
Punched cards and punched tapes are useful in storing data in the form a series of
punched holes along their length. Punched tapes may be made of paper, a plastic material
known as mylar or Aluminium foils. Magnetic tapes are made of plastic material and are
coated with Gamma ferric oxide layer. The advantages of magnetic tapes as input media are
(i) their greater strorability and (ii) data can be erased and be reused.
9.3.2 Machine Control Unit (MCU)
Machine Control Unit consists of electronic circuits (hardware) that are useful in
reading and interpreting the instructions (NC program) fed by means of input media and
convert them into mechanical actions of the machine tool.
Generally, the MCU may be of three types
(i)
Inbuilt type
(ii)
Swing around type
(iii)
Stand alone type
Fig 9.2 In-built MCU
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Inbuilt MCU
When the control unit of the NC machine is housed in the construction of the machine
itself, it is known as Inbuilt MCU. Fig. 9.2 shows a inbulit MCU.
Swing atound MCU
This MCU is a separate unit and is connected to the machine by a swinging
arrangement. The unit as a whole can be swung around the machine depending upon the
position of the operator. Fig. 9.3 shows a swing around MCU.
Fig 9.3 Swing around MCU
Stand alone MCU
Stand alone MCU is designed as a separate unit and placed at a distance from the
machine.
Fig. 9.4 shows a stand alone MCU.
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Fig 9.4 Stand alone MCU
Elements of a Machine Control Unit
In general, a Machine Control Unit consists of following elements
1. Input reading unit
2. Memory unit
3. Processing unit
4. Output channels
5. Feedback unit
Input reading unit
It is a electro - magnetic device useful in reading the NC programs in the form of
instructions.
The main functions of a input reading unit are
1. To accept the input media like punched cards, punched tapes, magnetic tapes and
floppy disks
2. To send them into a reading unit to extract the information stored in them
3. To process the collected information
4. To collect the input media to be used again
Different types of reading equipments are used to extract the stored data from punched
cards and punched tapes. They may be of mechanical, optical or pneumatic type. Magnetic
tape readers are used to retrieve the data from magnetic tapes and disks.
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Memory unit
A block of information received from the input media consists of words and codes.
Sequential informations are arranged in a desired order as separate blocks. These blocks of
informations are stored in a temporary memory known as buffer memory. The memory unit
will provide the information blocks to the processing unit in the desired sequence.
Processing unit
The processing unit serves as a link between the memory unit and output channels.
The processor does the duty of co-ordinating and controlling the other units of the MCU.
The informations received from the buffer are processed here and appropriate signals are
given to various units at particular points of time. Until a few years ago, processors made
use of vacuum tubes and transistors. But recently, when the era of Integrated Circuits (IC)
has dawn, processors are driven by ICs.
Output channels
Mostly output channels are the pins found on ICs or the wires coming out of
processors. These channels emit electric pulses of very low voltage / current. The pulses are
the result of processed information based on the NC program. In order to drive or actuate
various slides of the machines, the pulses are amplified by means of electronic or
electro - magnetic amplifiers or thyristors.
Feedback unit
Feedback unit consists of some electrical or electronic hardware. This is used for
converting physical quantities like displacement or velocity into electrical pulses. This
system is used in a NC system to check whether the operations are carried out in accurate
manner.
The system of operation of a NC machine mainly depends upon the accurate displacement of slides and proper speed of driving units. The actual quantity of these factors
during the operation is measured, converted as electrical pulses and sent back to processing
unit for checking.
The devices used to convert one form of physical quantity into electrical pulses is
known as transducers. Transducers used in a NC system are of two types
1. Velocity transducers
2. Position transducers
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Velocity transducers:- They are used to measure spindle speed and slide velocity.
An electric tachometer can be used as a velocity transducer.
Position transducer :- They are used to measure slide displacement.
9.3.3 Driving devices
Driving devices consist of different types of motors and gear trains. They convert
the instructions form the MCU into accurate mechanical displacements of the machine tool
slides. The motors may be electrical, hydraulic or pneumatic.
Electrical motors are mainly used as prime movers because of their speed and torque
characteristics. A.C. induction motors are cheap and easy to maintain. For easy and
effective speed changes, D.C. motors are also used.
Hydraulic motors are used in some specific types of CNC machines. Hydraulic
motors get the drive from oil pumped from a constant delivery hydraulic pump. Hydraulic
motors are used where the load is high and wider range of speed is necessary.
Servomotor, stepper motor, synchros and resolvers are different types of motors
used as drives in NC machines.
9.3.4 Manual control unit
Manual control unit consists of dials and switches to be operated by the
operator. It may also have a display unit to provide useful informations to the operator. In
some machines, the manual control unit may be a part of the MCU (machine control unit)
The operator use the manual contrl unit to
1. switch on and off the machine
2. load and unload the workpieces and
3. change the tools in certain types of machines
9.3.5 Machine tool
It is the element of the NC machine which actually performs the useful work
of converting the raw material to finished components. It is designed to perform various
machining operations. It consists of a machine table, spindles, cuttingtools, work holding
devices such as jigs and fixtures, coolant systems, swarf removal systems and other
auxiliary equipments.
207
208
Fig 9.5 Lay out of a NC machine tool
9.4 Classification of NC machine tools
According to various features, NC machine tools are classified as the following
A. According to the type of power to the drives
a. Electrical
b. Hydraulic
c. Pneumatic
B. According to motion control system of slides
a. Point- to - point system
b. Contour (or) continuous path system
C. According to the feedback system
a. Open loop system
b. Closed loop system
D. According to axis identification
a. 2- axis
b. 3- axis
c. 4- axis
d. 5- axis
9.5 Motion control system
The cutting tool and the work are located at certain postions in NC machine. During
the machining, they are moved from their positions with relation to each other. The system
involved in moving the cutting tool and the work is known as motion control system.
9.5.1 Point - to - point motion control system
It is a system in which the cutting tool is located at a particular point in relation to the
work. Machining is performed only after the cutting tool and the work are located at
defined positions and there will not be any change in their positions during machining. This
system is also called positioning system for this reason. When machining at the particular
position is over, the cutting tool (or) the work (or) both are moved to be relocated to
different points for subsequent machining. The relocation is achieved by their movement in
two main axes (x axis and y axis). This is the reason for this system to be called as
point - to - point system. The NC machines with point to point system are simple in
construction and are cheaper. They are adapted for drilling machines, jig boring machines
and spot welding machines.
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9.5.2 Continuous path motion control system
In this system, both the cutting tool and the work change their positions during
machining. The movement of the cutting tool and the work is simultaneous in all axes and in
all planes each at different speed. This system is also called as contouring system and is
mainly used in milling machine.
9.6
Feedback System
In NC machine system, the instructions are picked from the punched card or tape by
the reading Unit. Processors send electric pulses which actuate the motors and slides to
govern the movement of the spindle or tables. A control system is necessary to check the
actual output movement with the desired value as given in the input. This system is known as
feedback system.
9.6.1 Open loop System
When a NC system does not have any feedback arrangement, it is known as open
loop system. Actual output movement is not directly measured and checked with the desired
movement.
9.6.2 Closed loop system
In this system, the final movements (spindle speed and slide displacement) are
compared and balanced with the values given through the input commands. The movements
of spindle and slides are measured by feedback devices like velocity transducers and
position transducers and sent back to control unit for comparing. If the feedback values
does not match with the input values, the difference is corrected. This system is adopted
where highest positional accuracy is required.
9.7
Advantages of CNC machines over conventional machine tools
With the advent of CNC machines, several advancements are seen in the field of
manufacturing. The advancements prove to be very advantageous when comparing them
with convetional machine tools. The advantages are
1. The process of production planning becomes easy and effective.
2. As the CNC machines are capable of doing several machining operations, the output
of a single CNC machine is equivalent to the output of many conventional machines.
3. The above fact ensures a considerable reduction of floor space and storage space.
4. The lead time required for the preparation of punched cards and tapes is very less
when compared with the preparation of jigs and fixtures.
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5. Parts can be run economically in smaller quantities and it reduces the inventory.
6. The design change of the component (if necessary) can be done easily and quickly.
7. As the CNC machines require very little attention of the operator, the machine
utilisation is better.
8. Expensive jigs and fixtures are not necessary for location and holding. It reduces the
tooling costs.
9. Production of a workpiece requires very few set ups because more operations can
be performed at each set up of the work.
10. The accuracy achieved is very high. It leads to better assembly and reduces fitting
costs. The quality of the product also becomes better.
11. Operator errors are substantially reduced and so very less scrap is produced.
12. As a single operator can supervise several machines at a time, the labour cost is reduced.
9.8 Programming for CNC machines
Based on the component drawing, a lot of informations are needed to be fed into the
control unit for processing and machining. The informations include dimensions, shape, cutting speed, feed, depth of cut, sequence of operations, tool and work material. The said
informations should be fed into the machine control unit in an acceptable form. Preparation
of the instructions in the above form is known as programming.
9.8.1 Part program
A series of instructions describing the part to be produced in an acceptable form to
the control unit or computer is known as part program. Generally part programming is done
by the following methods.
1. Manual part programming
2. Computer assisted part programming.
APT (Automatically Programmed Tools), ADAPT, EXAPT, SPLIT, PROMPT are
some of the high level languages used for writing NC programs.
9.9 Advancements in NC machines
After the modern micro-processor based computers took control of the NC system,
the technology in this field has grown tremendously. Following are two major advancements
of NC system.
1. Direct Numerical Control (DNC)
2. Adaptive Control (AC)
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9.9.1 Direct Numerical Control (DNC)
A manufacturing system in which several NC machines are connected to and
controlled by a remotely located main frame computer, is known as Direct Numerical
Control. The basic constituents of the system are (i) Main frame computer (ii) Bulk memory
(iii) Nerwork system and (iv) NC machine tools.
DNC system eliminates the need of separate machine control units, input media like
punched card and tapes. This system looks after the scheduling of work of all the NC
machine tools. The required network system may be a LAN (Local Area Network) or a
WAN (Wide Area Network).
9.9.2 Adaptive Control
Adaptive control is a system in which an important feature of decision making is
employed during machining. When a component is being manufactured, some important
process variables like torque, force and temperature are measured. These values are
compared with established limits. On comparison, the process of production is modified by
the adjustment of cutting speed, feed and depth of cut. This system enables cost effective,
quality and high rate of production.
QUESTIONS
I.A. Choose the correct option
1. Production is achieved by
a. man and machine
c. men, machine, materials and tools
b. materials and tools
d. men and tools
2. In NC system, the program instructions are given as
a. information
b. numerical data
c. symbols
d. encryption
3. IC refers to
a. Information Control
c. Internal Control
b. Instruction Control
d. Integrated Circuits
4. Easy and effective speed changes can be done with
a. Electrical motors
b. D.C.motors
c. A.C.induction motors
d. Hydraulic motor
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5. Output channels are found as pins on the
a. memory unit
b. feedback unit
c. processors
d. driving devices
6. Transducers are
a. feedback devices
c. output channels
b. memory unit
d. processors
7. When a NC system does not have any feedback arrangement, it is known as
a. positioning system
b. contouring system
c. closed loop system
d. open loop system
8. Diredt Numerical control (DNC) needs
a. On-site supervisors
c. network system
b. adaptive control
d. feedback system
I B. Answer the following questions in one or two words
1. What are numbers used in binary format of numbering?
2. Expand - MCU.
3. Name two input media used in NC systems.
4. How is temporary memory otherwise known as?
5. What is the main duty of the processing unit?
6. What do the output channels emit?
7. What are the types of transducers?
8. How are NC machine tools classified according to feedback system?
9. What are the motion control systems in NC systems?
10. Name two major advancements of NC systems?
II. Answer the following questions in one or two sentences
1. Define - Numerical Control.
2. What do you mean by software of a NC system?
3. What is Machine Control Unit?
4. What are the types of MCU?
5. Mention the functions of input reading unit?
6. How is processing unit important in a NC system?
7. Write short notes on ‘Output channels’.
8. What is manual control unit?
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9. What are the uses of manual control unit?
10. How are NC machine tools classified?
11. What is motion control system?
12. Define - Part program.
13. Name some high level languages used to write NC programs?
14. What is Direct Numerical Control?
15. What is Adaptive Control?
IV. Answer the following questions in about a paragraph
1. Explain a NC system.
2. Explain (i) software (ii) input media.
3. What is MCU? Explain its types?
4. Explain driving devices of a NC system?
5. Explain the types of feedback system?
6. Briefy explain the advancements in NC machines.
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10. MACHINE TOOL MAINTENANCE
10.1 Introduction
“Prevention is better than cure”. With reference to this proverb, the task
performed to make the machine tools work perfectly is called ‘Maintenance’. This is achieved
by ensuring that machine tools, cutting tools and measuring instruments function properly
without any fault.
10.2. The objective of ‘Maintenance’
The primary objective of the maintenance department is to ensure the machine tools,
instruments, tools and accessories in good working condition. It is also necessary to ensure
safety to both the machine tools and the operator. The accuracy and efficiency of the
machine tools and the instruments are also to be maintained properly. By performing
maintenance, we can avoid accidents inside the workshop and increase the production
capacity.
All the machine tools are driven by electrical motors. It is necessary that the switches,
fuse, the connections and other controls should be in order. Care should also be taken to
keep in good conditions the parts used for transmitting power from the motor – gears, chain
drive, belt drive etc.,
The rotating shafts of the machine tools are fitted with bearings and suitably supported
by different types of brackets. As bearings are precision parts, we have to apply grease or any
lubricating oil at recommended intervals to keep them in good operating conditions. The
sliding parts of various machine tools should be maintained cleanly without any dirt on them.
The metal chips should be cleaned at regular intervals.
The moving and rotating parts should be properly lubricated at the brackets where
they are fitted.
The coolant pumps, filter elements, pipelines and valves should always be in good
working condition.
215
The tools, accessories, special attachments and measuring instruments should be in good
working conditions and be placed in their respective places.
10.3 Wear & tear and backlash
Wear and tear
Due to continuous working of a machine tool and the nature of work performed on it,
wear and tear is observed in the sliding parts of machine tools. As a result of this, the
accuracy of the products is affected. In remedy, it is necessary to repair the said machine
tools. The affected parts are to be replaced if necessary.
Backlash
Some slackness is observed in holding of parts, meshing gears or bolt and nut
assembly. This slackness is known as backlash. If the amount of backlash is more in the
case of mating gears, they should be replaced. The wear and tear on the gears should be
observed once in a week time.
10.4 Machine tools
The term machine tools refers not only the cutting tool. It means the machines,
cutting tools, attachments, measuring instruments and accessories.
10.5 Lubrication
Rotating and sliding parts, which make contact with other parts, are subjected to
wear due to friction. Viscous oil called lubricant is applied to these parts to avoid direct
contact between them. The process of reducing friction is called lubrication.
Applying oil or grease to the axle shaft of the bullock cart and the cycle wheel,
gearbox of automobiles, motor shafts of pumps, fans and sewing machine are some
examples of lubrication.
Friction occurs as the shafts are rotating and the sliding parts moving on each other.
It generates heat and the parts get damaged.
In order to keep the machine tools accurate and durable, it is necessary to apply
lubricants between mating parts. It will reduce friction and wear is minimised.
Lubrication is the nerve centre of machine tool. As it is blood circulation for the
human body, lubrication is for the machine tools.
216
10.5.1 The machine parts which need to be lubricated
1. Mechanisms of hydraulic systems
2. Guideways and sliding parts
3. Rotating shafts
4. Gear box
5. Feed box
6. Speed changing mechanisms
7. Bearings
10.5.2 Objectives of lubrication
1. Smooth functioning of sliding and moving parts
2. To reduce friction and consequent wear
3. To remove burrs and dust
4. To reduce the heat generated due to friction
5. To prevent rust formation on precise parts
6. To provide cushioning effect to the load shocks
7. For hydraulic circuits to transmit power
10.5.3 Types of lubricants
The materials used for reducing wear between moving and sliding parts are called
lubricants. Though there are many types of lubricants available, oil and grease are mostly used.
Grease
Grease is manufactured with the ingredients of soap and mineral oils. Different types
of grease are manufactured for specific applications under different commercial names. So,
it is necessary to know the specific type of grease to be applied for the specific part.
10.6 Methods of lubrication
The different methods of lubrication are
1. Ring lubrication
2. Wick lubrication
3. Splash lubrication
4. Grease lubrication
217
10.6.1 Ring lubrication
The method of ring lubrication involves a ring hanging from down the rotating shaft.
The bottom portion of the ring is immersed in the oil container. When the shaft starts
rotating, the ring also rotates. While the ring rotates, it carries a small amount of oil and the
oil is spread into the bearing and the shaft. Fig.10.1 illustrates ring lubrication.
Oil hole
Metal
bushing
Ring
Oil
Fig. 10.1 Ring lubrication
10.6.2 Wick lubrication
Wick lubrication is a method in which the wick along with a flexible thin piece of
metal is used. A container having oil is placed above the bearing. The wick connects the
container and the part to be lubricated. This lubrication enables the oil to flow from the
container to the required place. Wick lubrication is illustrated in Fig. 10.2.
10.6.3 Splash lubrication
The rotating part of the machine itself is made to be immersed in the oil container.
When the part starts rotating, the oil is splashed and the moving parts are lubricated.
Bearings are generally lubricated by this method. Little spoons are attached to the rotating
parts to get more quantity of oil to the part to be lubricated.
218
Wick
Oil
Fig. 10.2 Wick lubrication
10.6.4 Grease lubrication
Grease lubrication is done with the help of grease guns. Another way of doing it
simply is to fill a container with grease and the container is connected to the parts to be
lubricated by means of a small tube. When a screw is screwed into the container, a good
amount of grease is taken to the required place. Fig. 10.3 shows a grease gun.
Handle
Grease
filling
port
Grease
outlet
Fig. 10.3 Grease gun
219
Lubricating oil and grease are manufactured under several trade names by the Indian
oil companies. Suitable lubricants are used for specific purposes.
10.7 Central maintenance department
The primary aim of maintenance department is to ensure the machine tools,
instruments, tools and accessories in good working conditions. More maintenance attention
is needed when the work load increases. If the machines are maintained properly, we can
lookout for more production.
Separate maintenance department will be functioning in major machine shops and
industries. Experienced engineers, supervisors, technicians will be working in this
department. Separate equipments and instruments will be used in the department.
10.8 Types of maintenance
There are different types of maintenance and they are
1. Routine maintenance
a. Daily maintenance
b. Weekly maintenance
2. Preventive maintenance
3. Breakdown maintenance
4. Capital repairs or Corrective maintenance
10.8.1 Routine maintenance
Routine maintenance is done to avoid unnecessary breakdown of machine tools. It
involves regular works like cleaning and lubricating, making minor adjustments and doing
small repair works.
It is important to chart out what are all to be done daily, weekly and monthly.
Daily maintenance
1. Cleaning all the parts of the machine tool
2. Lubricating the movable parts with grease and oil as per requirements
3. To correct the machine tool to make it operate accurately
4. To look at whether the coolant supply and auto lubricating equipments are
working properly
5. To remove the burrs cleanly
220
Weekly maintenance
1. The measuring instruments, gauges and hand tools are checked and corrected
if necessary.
2. The spare parts and integral parts of the machine tools should be cleaned.
3. The entire workshop premises should be maintained cleanly.
4. Grinding wheels of bench grinders and tool and cutter grinders should be dressed.
The work rests of these machines should be adjusted properly.
5. The protective devices in the machine tool are checked whether they are properly
fixed. And they are corrected if necessary.
6. The cables and electrical connections should be checked.
7. The position and working of belt, chain etc., are checked and adjusted.
8. Parts like gears, clutches and bearings are checked for their proper functioning.
9. The accuracy of precision measuring instruments are checked and corrected. They
are also checked for zero error.
10.8.2 Preventive maintenance
In order to avoid sudden breakdown of machine tools and major repairs, a complete
maintenance programme is charted out. This will ensure that there is no slip in the rate of
production.
In case of any major breakdown to the machine tool, two types of losses are
incurred to the management.
1. Direct losses
2. Indirect losses
Direct loss is the expenditure incurred for repairing the machine tools and getting
them back in action.
Indirect losses happen by the loss of income for the disturbed production. The
management has to pay the labourers their wages. It will also be earning a bad name due to
non - deliverance of the products to its customers. So, it is necessary to plan the preventive
maintenance program to avoid such losses.
Even if the machine tools are working in proper conditions, it is better to stop
production once in a while to make the necessary repairs and adjustments. Certain parts
should be replaced if necessary.
221
10.8.3 Breakdown maintenance
Even after enforcing routine maintenance and preventive maintenance, there are
chances that some machine parts may fail due to some reason or other. In order to bring
back the machine to its original working condition, some minor or major repairs are needed
to be done. This type of maintenance is known as breakdown maintenance.
10.8.4 Corrective maintenance
Even if the machine is functioning properly, it is necessary to halt the functioning of
the machine to do some major repair once is a year. To do that, the machine parts are to be
dissembled completely and worn out parts are replaced. Some parts of the machine may be
in a condition that they need to be replaced soon. To correct all such difficulties, the
machine is stopped from functioning to do all and every repairs to bring back the machine to
accurate machining conditions. This called as corrective maintenance.
10.9 Planned maintenance programme
The main objective of planned maintenance programme is to increase the production
by keeping the machine tools always ready in good condition. It is done by keeping the
machine tools to perform all the activities correctly with the required accuracy at desired
speed with full safety protection.
The planned maintenance programme is to be prepared and executed as follows.
1. When a new machine tool arrives to the machine shop or the existing machine
tools are to be replaced, it is required to install the machine tools properly, level and align
them correctly and connect them to the electrical terminals safely.
2. If errors are found in the dimensional accuracy, the errors should be recorded and
analysed whether the machine is in bad condition.
3. It is necessary to plan and get ready the materials, spares and tools required for
the maintenance in advance so that the maintenance work is carried out in time.
4. The operators and supervisors should know the importance of the cutting speed,
feed data of the machine tools.
5. Emergency repair works should be done without any delay in the case of
breakdown of any of the machine tools.
222
6. The machine should be overhauled if the working efficiency of the machine tool
goes below a particular level.
7. If the machine tools become very old and not performing to the desired level, it
has to be dismantled completely and worn out parts should be replaced to bring it to the
normal working condition.
8. The following details should be prepared and made as charts : the layout plan of
the shop, the size and specification of the machine tools and the parts to be lubricated. The
manuals and the list of spare parts of all the machine tools are also to be kept ready.
9. Annual budget for the maintenance work should be prepared atleast six months or
one year in advance.
10.10 Materials and instruments needed for doing maintenance
1. Steel rule
2. Try-square
3. Calipers
4. Micrometer
5. Vernier calipers
6. Gauges
7. Vice
8. Files
9. Tap & Die
10. Spanner set
11. Hammers
12. Screw drivers
13. Wrenches
14. Hacksaw frame & blades
15. Lubricating devices
16. Emery sheets
17. Scraper
223
QUESTIONS
I. Answer the following questions in one or two words
1. Name any one method of lubrication.
2. Name any two instruments required for doing maintenance.
II. Answer the following questions in one or two sentences
1. What is direct loss?
2. What do you mean by indirect loss?
3. What is machine tool maintenance?
4. What is the objective of maintenance?
5. What are the types of maintenance?
6. What is preventive maintenance?
7. What is ‘wear’?
8. What is backlash?
9. What is breakdown maintenance?
10. Define - ‘Corrective maintenance’.
11. What is lubrication?
12. What are the parts which need to be lubricated?
III. Answer the following questions in about a page
1. What are the objectives of lubrication?
2. Explain ‘Ring lubication’ with a diagram.
3. Explain ‘Wick lubrication’ with a diagram.
4. ‘Grease lubrication’ - Explain.
5. Explain ‘Routine maintenance’.
6. Explain ‘Planned maintenance programme’.
224
225
1
15
CNC Machines
Machine tool maintenance
Total questions
9
10
Marks
1
Welding
8
15
1
1
1
15
1
1
1
1
1
2
2
2
2
2
4 marks
15x1=15 15x1=15 10 x 4 = 40
1
1
Electrical equipments
7
1
1
1
Hydraulic equipments
2
6
2
2
2
Grinding machine
4
2
2
2
Shaping machine
3
2
2
Milling machine
Drilling machine
2
2
Objective 1 or 2 words
1 mark
Part - I
5
Lathe
Title
1
Sl. No.
6
-
-
1
-
-
1
1
1
1
1
20 marks
Part - IV
5 x 10 = 50 4 x 20 = 80
7
1
1
-
1
1
1
-
-
1
1
10 marks
Question allotment
Part - II
Part - III
QUESTION PAPER BLUE PRINT
200
Total
MODEL QUESTION PAPER
GENERAL MACHINIST
Time alloted : 3 hours
Maximum marks : 200
Part - I
30 x 1 = 30
A. Choose the correct option
1. Lathe was first developed by
a. Henry Maudslay
b. Eli Whitney
c. James Nasmith
d. Michael Faraday
2.Turret and capstan lathes are classified under
a. automatic lathes
b. semi-automatic lathes
c. bench lathe
d. tool room lathe
3. The lip clearance angle of a drill is
a. 59°
b. 118°
c. 12° to 15°
4. Reamer is a
a. multi point cutting tool
b. single point cutting tool
c. parting tool
d. 180°
d. saw teeth cutting tool
5. The part involved in reciprocation by quick return is
a. table
b. ram
c. column
d. crossrail
6. The mechanism used to move the shaper table automatically is
a. back gear mechanism
b. crank & slotted link mechanism
c. tumbler gear mechanism
d. ratchet & pawl mechanism
7. The heat generated during dry grinding will be
a. 2000°C
b.20°C
c. 1000°C
8. Bond used for making elastic grinding wheel is
a. vitrified
b. silicate
c. shellac
d. 1200°C
d. resinoid
9. The amount of table travel a milling machine is controlled by
a. saddle
b. trip dogs
c. cross-slide
d. elevating screw
10. The distance travelled by a point on a milling cutter in one minute is known as
a. cutting speed b. depth of cut
c. spindle speed
d. feed
11. Impeller is a part found in
a. reciprocating pump
c. centrifugal pump
b. gear pump
d. vane pump
226
12. Starter used for motors of capacity upto 5 hp is
a. star – delta starter
b. Direct – on – line starter
c. auto transformer starter
d. rotor resistance starter
13. Atomic hydrogen welding is a ------------ process
a. gas welding
b. resistance welding
c. arc welding
d. solid state welding
14. Transducers are
a. feedback devices
b. memory unit
c. output channels
d. processors
15. Maintenance done once a year is known as
a. breakdown maintenance
b. routine maintenance
c. corrective maintenance
d. preventive maintenance
B. Answer the following questions in one or two words
16. Name a device useful in holding a long workpiece.
17. Name the operation performed in a lathe by offsetting the tailstock.
18. Name the groove present on the drill.
19. Name the device useful in holding a cylindrical workpiece on drilling machine
table.
20. What type of surfaces are machined on a shaper?
21. Which part of the shaper is involved in automatic lifting of the tool during the return
stroke of the ram?
22. Name one artificial abrasive.
23. Name the grinding machine used for grinding jigs, fixtures and tools.
24. What is the base of a milling machine made of ?
25. Name the part which holds the other end of the arbor in a milling machine.
26. Which type of pump is a vane pump?
27. Name the windings present in the A.C. single phase capacitor start motor.
28. Which type of welding require filler rods?
29. What are the numbers used in binary format of numbering?
30. Name any one method of lubrication.
Part - II
Answer any ten questions in one or two sentences
31. What are the important parts of a lathe?
32. What is swing diameter in a lathe?
227
10 x 4 = 40
33. Define ‘cutting speed’ in a drilling machine.
34. State any two differences between the processes of reaming and boring.
35. What is the use of swivel toolhead of a shaping machine?
36. Name any two points in specifying the size of a shaping machine.
37. What is centreless grinding?
38. What is glazing?
39. What is milling?
40. What is the use of indexing head?
41. Mention the types of hydraulic pumps.
42. What are the safety devices fitted in starters to protect the induction motors?
43. What are the types of electrodes?
44. What is Machine Control Unit?
45. What is the objective of maintenance?
Part - III
5 x 10 = 50
Answer any five questions in about a page
46. List out the types of lathe.
47. Explain any two drill holding devices.
48. What are the differences between a plain milling machine and a universal milling
machine?
49. Draw the circuit of a hydraulic shaper and label its parts.
50. Draw and explain a D.O.L starter.
51. Explain (i) software (ii) input media.
52. Explain ‘Ring lubrication’ with a diagram.
Part - D
4 x 20 = 80
Answer any four questions in detail
53. Explain the back gear arrangement with a diagram.
54. Explain any four operations performed in a drilling machine.
55. Explain the crank & slotted link mechanism of quick return of the ram with a
diagram.
56. Draw and explain a external cylindrical grinder.
57. Explain any four cutter holding devices in a milling machine with diagrams.
58. Explain resistance welding with a diagram.
228
GENERAL MACHINIST
PRACTICAL I & II
VOCATIONAL EDUCATION
HIGHER SECONDARY - SECOND YEAR
A Publication under
Government of Tamilnadu
Distribution of Free Textbook Programme
( NOT FOR SALE )
Untouchability is a sin
Untouchability is a crime
Untouchability is inhuman
TAMILNADU
TEXTBOOK CORPORATION
College Road, Chennai - 600 006.
©
Government of Tamilnadu
First Edition - 2011
Chairperson
Dr. R. RAJKUMAR,
Head of the Department ( Mechanical )
AMK Polytechnic College,
Sembarambakkam, Chennai - 602 103.
Authors
G. JAYAKUMAR JESUDOSS,
Vocational Teacher,
Dharmamurthi Rao Bahadur Calavala Cunnan Chetty’s
Hindu Higher Secondary School,
Thiruvallur - 602 001.
C. RAVIVARMAN
A. VELAYUTHAM
Vocational Teacher,
Govt. Boys Higher Secondary School,
Nattrampalli,
Vellore Dist - 635 852.
Vocational Teacher,
Govt. Higher Secondary School,
Nemili,
Vellore Dist - 631 051.
B. PRABHAKARAN
N. PALANIVELU
Vocational Teacher,
Govt. Boys Higher Secondary School,
Vandavasi,
Thiruvannamalai Dist-604 408.
Vocational Teacher,
Govt. Boys Higher Secondary School,
Arni,
Thiruvannamalai Dist - 632 301.
This book has been prepared by the Directorate of School Education on behalf of the
Government of Tamilnadu
This book has been printed on 60 GSM paper
Printed by Web Offset at :
GENERAL MACHINIST PRACTICAL - I
CONTENTS
Ex. No.
Date
Title of the exercise
Page
No.
1.
Facing
8
2.
Facing and plain turning
10
3.
Step turning
14
4.
Step turning and chamfering
18
5.
Taper turning
22
6.
Knurling
26
7.
Grooving
30
8.
Undercutting
34
9.
Collar turning
38
10.
Plain and taper turning
42
iii
Teacher’s
signature
GENERAL MACHINIST PRACTICAL - II
CONTENTS
Ex. No.
Title of the exercise
Date
Page
No.
1.
Filing, marking & punching
46
2.
‘
’ cutting
50
3.
‘
’ cutting
54
4.
‘
’ cutting
58
5.
‘
’ cutting
62
6.
‘
’ cutting
66
7.
‘
’ cutting
70
8.
‘
’ cutting
74
‘
’ cutting
‘
’ cutting
9.
10.
78
82
iv
Teacher’s
signature
GENERAL MACHINIST
PRACTICAL - I
Note : All the dimensions are given in mm. The diameter of the round rod is given as 20 mm.
The design of the exercises may be modified accoding to the size of the material available.
1
2
Points to be considered while working on a lathe
Some important points are to be considered before setting on to work on a lathe.
They are
1. The suitable method of holding different types of work according to their shape.
2. Selection of proper cutting speed according to the size, weight, material of the
work and the type of the operation.
3. Selection of proper cutting tool.
4. Mounting of the selected tool on the tool post.
The following illustrations are given to provide a good idea of holding a work,
cutting speed, types of tools and setting of the tool.
Holding of the work
The method of setting the work in a four jaw chuck with the help of a surface gauge
3
A cylindrical work is held in a three jaw chuck
A rod of square section is held in a four jaw chuck
Cutting speed
Speed can be defined as the distance an object moves in a particular time. In a lathe,
the cutting speed is the distance travelled by a point on the outer surface of the work in one
minute. It is expressed in meters per minute.
πdn
Cutting speed = ——— m/min.
1,000
Where
‘d’ - is the diameter of the work in mm.
‘n’ - is the r.p.m. of the work.
4
Table showing cutting speed for various materials
Cutting tool material
Work material
High speed steel
Tungsten steel
Stellite
Mild steel
30 m/ min
80 m/ min
58 m/ min
High carbon steel
26 m/ min
65 m/ min
50 m/ min
Cast steel
15 m/ min
80 m/ min
42 m/ min
Cast iron
22 m/ min
80 m/ min
50 m/ min
Aluminium
90 m/ min
400 m/ min
330 m/ min
Brass
61 m/ min
200 m/ min
33 m/ min
Tools used in a lathe
A. According to the construction, the lathe tools are classified into three types
1. Solid tool
2. Brazed tipped tool
3. Tool bit and tool holders
B.According to the operation to be performed, the cutting tools are classified as
1. Turning tool
2. Thread cutting tool
3. Facing tool
4. Forming tool
5. Parting tool
6. Grooving tool
7. Boring tool
8. Internal thread cutting tool
9. Knurling tool
C. According to the direction of feed movement, the following tools are used
1. Right hand tool
2. Left hand tool
3. Round nose tool
5
Method of mounting the cutting tool on the tool post
Correct method
The cutting edge of the cutting tool is positioned exactly aligned to the axis of the
lathe spindle
Incorrect methods
6
If the cutting edge of the cutting tool is positioned above the axis of the lathe spindle,
the front clearance surface of the tool drags on the work. The cutting edge loses its cutting
capacity due to wear.
If the cutting edge of the cutting tool is positioned above the axis of the lathe spindle,
the cutting edge loses its keenness. When the tool is provided with depth of cut, the work
rides over the tool. The cutting edge may be broken and the work surface is damaged.
Types of toolposts
Single screw toolpost
Four way toolpost
7
Exercise - 1 (Facing)
Operation - 1
8
1. FACING
Aim
To machine a flat surface on the face of the given round rod (Facing)
Required instruments
1. Facing tool
2. Chuck key
3. Tool holder
4. Steel rule
5. Vernier caliper
6. Surface gauge
Tool setting
A facing tool is mounted on the toolpost and its cutting edge is set exactly aligned to
the axis of the lathe spindle. The compund rest is set at 0° mark.
Holding of the work
1. The metal piece to be machined is held in the chuck of the lathe.
2. Surface gauge is used to check whether the work is held aligning with the lathe
axis.
Selection of cutting speed
πdn
Cutting speed = ——— m/min.
1,000
The above formula is used to arrive at a proper cutting speed for machining and the
spindle speed is adjusted suitably.
Procedure
The lathe is switched on and the facing tool mounted on the toolpost is given feed by
the cross-slide perpendicular to the lathe axis. A flat surface on the face of the work is
generated.
Result
The finished piece of work is sent for inspection after the machining is over.
9
Exercise - 2 (Facing & plain turning)
Operation - 1
All dimensions are in mm
10
2. FACING AND PLAIN TURNING
Aim
To machine a flat surface on the face of the given round rod (Facing) and to perform
plain turning operation to produce a cylindrical part of given dimensions.
Required instruments
1. Facing tool
2. Plain turning tool
3. Chuck key
4. Tool holder
5. Steel rule
6. Vernier caliper
7. Outside caliper
8. Inside caliper
9. Surface gauge
Tool setting
A facing tool and a plain turning tool are mounted on the toolpost and their cutting
edges are set exactly aligned to the axis of the lathe spindle. The compund rest is set at 0°
mark.
Holding of the work
1. The metal piece to be machined is held in the chuck of the lathe.
2. Surface gauge is used to check whether the work is held aligning with the lathe
axis.
Selection of cutting speed
πdn
Cutting speed = ——— m/min.
1,000
The above formula is used to arrive at a proper cutting speed for machining and the
spindle speed is adjusted suitably.
11
12
Facing operation
The lathe is switched on and the facing tool mounted on the toolpost is given feed by
the cross-slide perpendicular to the lathe axis. A flat surface on the face of the work is
generated.
Marking
Marking is done on the work at the required point to indicate the length to be plain
turned.
Procedure
1. The cross-slide is adjusted for required depth of cut and the lathe is switched on.
The plain turning tool mounted on the tolpost is given feed by the carriage parallel to the
lathe axis.
2. The above process is repeated until the required diameter is obtained. This is
done by gradually moving the cross-slide after each cut.
3. During this process, the diameter of the work is checked with the help of outside
caliper.
4. Finishing tool is used to obtain accurate dimensions of length and diameter.
Result
The finished piece of work is sent for inspection after the machining is over.
13
Exercise - 3 (Step turning)
Operation - 1
Operation - 2
All dimensions are in mm
14
3. STEP TURNING
Aim
To perform step turning operation to produce a cylindrical part of given dimensions.
Required instruments
1. Facing tool
2. Plain turning tool
3. Chuck key
4. Tool holder
5. Steel rule
6. Vernier caliper
7. Outside caliper
8. Inside caliper
9. Surface gauge
Tool setting
A facing tool and a plain turning tool are mounted on the toolpost and their cutting
edges are set exactly aligned to the axis of the lathe spindle. The compund rest is set at 0°
mark.
Holding of the work
1. The metal piece to be machined is held in the chuck of the lathe.
2. Surface gauge is used to check whether the work is held aligning with the lathe
axis.
Selection of cutting speed
πdn
Cutting speed = ——— m/min.
1,000
The above formula is used to arrive at a proper cutting speed for machining and the
spindle speed is adjusted suitably.
15
16
Facing operation
The lathe is switched on and the facing tool mounted on the toolpost is given feed by
the cross-slide perpendicular to the lathe axis. A flat surface on the face of the work is
generated.
Marking
Marking is done on the work at the required point to indicate the length of the steps
to be turned.
Procedure
1. The cross-slide is adjusted for required depth of cut and the lathe is switched on.
The plain turning tool mounted on the tolpost is given feed by the carriage parallel to the
lathe axis.
2. The above process is repeated until the required diameter is obtained. The length
should be equal to the sum of the lengths of larger and smaller diameter.
3. When the larger step of given diameter is obtained, the tool is again fed parallel to
the lathe axis to the given length of smaller step. Depth of cut is gradually given by the
cross-slide to get the smaller step of required length and diameter.
4. Finishing tool is used to obtain accurate dimensions of length and diameter.
5. During this process, the dimensions of the work are checked with the help of
outside caliper and inside calipers.
Result
The finished piece of work is sent for inspection after the machining is over.
17
Exercise - 4 (Step turning and chamfering)
Operation - 1
Operation - 2
All dimensions are in mm
18
4. STEP TURNING AND CHAMFERING
Aim
To perform step turning and chamfering operations to produce a cylindrical part of
given dimensions.
Required instruments
1. Facing tool
2. Plain turning tool
3. Chamfering tool
4. Chuck key
5. Tool holder
6. Steel rule
7. Vernier caliper
8. Outside caliper
9. Inside caliper
10. Surface gauge
Tool setting
A facing tool, a plain turning tool and a chamfering tool are mounted on the toolpost
and their cutting edges are set exactly aligned to the axis of the lathe spindle. The compund
rest is set at 0° mark.
Holding of the work
1. The metal piece to be machined is held in the chuck of the lathe.
2. Surface gauge is used to check whether the work is held aligning with the lathe
axis.
Selection of cutting speed
πdn
Cutting speed = ——— m/min.
1,000
The above formula is used to arrive at a proper cutting speed for machining and the
spindle speed is adjusted suitably.
19
Operation - 3
20
Facing operation
The lathe is switched on and the facing tool mounted on the toolpost is given feed by
the cross-slide perpendicular to the lathe axis. A flat surface on the face of the work is
generated.
Marking
Marking is done on the work at the required point to indicate the length of the steps
to be turned.
Procedure
1. The cross-slide is adjusted for required depth of cut and the lathe is switched on.
The plain turning tool mounted on the tolpost is given feed by the carriage parallel to the
lathe axis.
2. The above process is repeated until the given larger diameter is obtained. The
length should be equal to the sum of the lengths of larger and smaller diameter. When the
larger step of given diameter is obtained, the tool is again fed parallel to the lathe axis to the
given length of smaller step. Depth of cut is gradually given by the cross-slide to get the
smaller step of required length and diameter.
3. During this process, the dimensions of the work are checked with the help of
outside caliper and inside calipers.
4. Finishing tool is used to obtain accurate dimensions of length and diameter.
5. The chamfering tool (form tool) is set at the end of the work at the required angle.
Feed is given to the tool by the cross-slide to perform chamfering.
Result
The finished piece of work is sent for inspection after the machining is over.
21
Exercise - 5 (Taper turning)
Operation - 1
All dimensions are in mm
22
5. TAPER TURNING
Aim
To perform taper turning to produce a cylindrical part of given dimensions.
Required instruments
1. Facing tool
2. Plain turning tool
3. Chuck key
4. Tool holder
5. Steel rule
6. Vernier caliper
7. Outside caliper
8. Inside caliper
9. Surface gauge
Tool setting
A facing tool, and a plain turning tool are mounted on the toolpost and their cutting
edges are set exactly aligned to the axis of the lathe spindle. The compund rest is set at 0°
mark.
Holding of the work
1. The metal piece to be machined is held in the chuck of the lathe.
2. Surface gauge is used to check whether the work is held aligning with the lathe
axis.
Selection of cutting speed
π dn
Cutting speed = ——— m/min.
1,000
The above formula is used to arrive at a proper cutting speed for machining and the
spindle speed is adjusted suitably.
23
24
Facing operation
The lathe is switched on and the facing tool mounted on the toolpost is given feed by
the cross-slide perpendicular to the lathe axis. A flat surface on the face of the work is
generated.
Marking
Marking is done on the work at the required point to indicate the length of the steps
to be turned.
Procedure
1. The angle(Ø) through which the compound slide is to be swiveled is calculated by
the formula
D-d
tan Ø = ---------2l
Where
‘D’ is the larger diameter
‘d’ is the smaller diameter and
‘l’ is the length of the taper
2. The compound slide is swiveled to the angle calculated as above.
3. The depth of cut is set by adjusting the cross-slide.
4. The plain turning tool mounted on the toolpost is given feed by the compund slide
at the required angle to the lathe axis.
5. The above process is repeated until the taper of required length is obtained. This
is done by adjusting the cross-slide for depth of cut and compound slide for feed.
6. While doing so, feed is provided from smaller diameter to larger diameter.
Result
The finished piece of work is sent for inspection after the machining is over.
25
Exercise - 6 (Knurling)
Operation - 1
All dimensions are in mm
26
6. KNURLING
Aim
To perform knurling operation on a cylindrical part of given dimensions.
Required instruments
1. Facing tool
2. Plain turning tool
3. Knurling tool holder
4. Chuck key
5. Tool holder
6. Steel rule
7. Vernier caliper
8. Outside caliper
9. Inside caliper
10. Surface gauge
Tool setting
A facing tool and a plain turning tool are mounted on the toolpost and their cutting
edges are set exactly aligned to the axis of the lathe spindle. The compund rest is set at 0°
mark.
Holding of the work
1. The metal piece to be machined is held in the chuck of the lathe.
2. Surface gauge is used to check whether the work is held aligning with the lathe
axis.
Selection of cutting speed
πdn
Cutting speed = ——— m/min.
1,000
The above formula is used to arrive at a proper cutting speed for machining and the
spindle speed is adjusted suitably.
27
28
Facing operation
The lathe is switched on and the facing tool mounted on the toolpost is given feed by
the cross-slide perpendicular to the lathe axis. A flat surface on the face of the work is
generated.
Marking
Marking is done on the work at the required points to indicate the length of the
portion to be knurled.
Procedure
1. The cross-slide is adjusted for required depth of cut and the lathe is switched on.
The plain turning tool mounted on the tolpost is given feed by the carriage parallel to the
lathe axis.
2. The above process is repeated until the required diameter is obtained. This is
done by gradually moving the cross-slide after each cut.
3. During this process, the diameter of the work is checked with the help of outside
caliper and inside caliper.
4. Finishing tool is used to obtain accurate dimensions of length and diameter.
5. A knurling tool holder has one or two knurling rolls fitted to it. It is fitted on the
toolpost and pressed against the work rotating at a slower speed. The feed is given by the
carriage parallel to the lathe axis.
6. The knurling tool holder is relieved from the work after the operation is performed
for the required length.
Result
The finished piece of work is sent for inspection after the machining is over.
29
Exercise - 7 (Grooving)
Operation - 1
Operation - 2
All dimensions are in mm
30
7. GROOVING
Aim
To machine a groove of given width and depth on a cylindrical part of given
dimensions.
Required instruments
1. Facing tool
2. Plain turning tool
3. Parting tool
4. Chuck key
5. Tool holder
6. Steel rule
7. Vernier caliper
8. Outside caliper
9. Inside caliper
10. Surface gauge
Tool setting
A facing tool, a plain turning tool and a parting tool are mounted on the toolpost and
their cutting edges are set exactly aligned to the axis of the lathe spindle. The compund rest
is set at 0° mark.
Holding of the work
1. The metal piece to be machined is held in the chuck of the lathe.
2. Surface gauge is used to check whether the work is held aligning with the lathe
axis.
Selection of cutting speed
πdn
Cutting speed = ——— m/min.
1,000
The above formula is used to arrive at a proper cutting speed for machining and the
spindle speed is adjusted suitably.
31
32
Facing operation
The lathe is switched on and the facing tool mounted on the toolpost is given feed by
the cross-slide perpendicular to the lathe axis. A flat surface on the face of the work is
generated.
Marking
Marking is done on the work at the required points to indicate the location of the
groove after plain turning is performed to the required diameter.
Procedure
1. The cross-slide is adjusted for required depth of cut and the lathe is switched on.
The plain turning tool mounted on the tolpost is given feed by the carriage parallel to the
lathe axis.
2. The above process is repeated until the required diameter is obtained. This is
done by gradually moving the cross-slide after each cut.
3. During this process, the diameter of the work is checked with the help of outside
caliper and inside caliper.
4. Finishing tool is used to obtain accurate dimensions of length and diameter.
5. The parting tool is brought to the marked location of the groove. The depth of cut
is set by the cross-slide and the feed is provided by moving the carriage slowly between the
marked points.
6. The above process is repeated until the required depth and the length of the groove
is obtained.
Result
The finished piece of work is sent for inspection after the machining is over.
33
Exercise - 8 (Undercutting)
Operation - 1
Operation - 2
All dimensions are in mm
34
8. UNDERCUTTING
Aim
To machine a undercut groove of given width and depth on a cylindrical part of given
dimensions.
Required instruments
1. Facing tool
2. Plain turning tool
3. Parting tool
4. Chuck key
5. Tool holder
6. Steel rule
7. Vernier caliper
8. Outside caliper
9. Inside caliper
10. Surface gauge
Tool setting
A facing tool, a plain turning tool and a parting tool are mounted on the toolpost and
their cutting edges are set exactly aligned to the axis of the lathe spindle. The compund rest
is set at 0° mark.
Holding of the work
1. The metal piece to be machined is held in the chuck of the lathe.
2. Surface gauge is used to check whether the work is held aligning with the lathe
axis.
Selection of cutting speed
πdn
Cutting speed = ——— m/min.
1,000
The above formula is used to arrive at a proper cutting speed for machining and the
spindle speed is adjusted suitably.
35
36
Facing operation
The lathe is switched on and the facing tool mounted on the toolpost is given feed by
the cross-slide perpendicular to the lathe axis. A flat surface on the face of the work is
generated.
Marking
Marking is done on the work at the required points to indicate the location of the
undercut groove after plain turning is performed to the required diameter.
Procedure
1. The cross-slide is adjusted for required depth of cut and the lathe is switched on.
The plain turning tool mounted on the tolpost is given feed by the carriage parallel to the
lathe axis.
2. The above process is repeated until the required diameter is obtained. This is
done by gradually moving the cross-slide after each cut.
3. During this process, the diameter of the work is checked with the help of outside
caliper and inside caliper.
4. Finishing tool is used to obtain accurate dimensions of length and diameter.
5. The parting tool is brought to the marked location of the groove. The feed is
provided by moving the cross-slide slowly into the work perpendicular to the lathe axis.
6. The above process is repeated until the required depth and the length of the groove
is obtained.
Result
The finished piece of work is sent for inspection after the machining is over.
37
Exercise - 9 (Collar turning)
Operation - 1
Operation - 2
All dimensions are in mm
38
9. COLLAR TURNING
Aim
To machine a collar of given width on a cylindrical part of given dimensions.
Required instruments
1. Facing tool
2. Plain turning tool
3. Parting tool
4. Chuck key
5. Tool holder
6. Steel rule
7. Vernier caliper
8. Outside caliper
9. Inside caliper
10. Surface gauge
Tool setting
A facing tool, a plain turning tool and a parting tool are mounted on the toolpost and
their cutting edges are set exactly aligned to the axis of the lathe spindle. The compund rest
is set at 0° mark.
Holding of the work
1. The metal piece to be machined is held in the chuck of the lathe.
2. Surface gauge is used to check whether the work is held aligning with the lathe
axis.
Selection of cutting speed
πdn
Cutting speed = ——— m/min.
1,000
The above formula is used to arrive at a proper cutting speed for machining and the
spindle speed is adjusted suitably.
39
40
Facing operation
The lathe is switched on and the facing tool mounted on the toolpost is given feed by
the cross-slide perpendicular to the lathe axis. A flat surface on the face of the work is
generated.
Marking
Marking is done on the work at the required points to indicate the location of the
collar after plain turning is performed to the required diameter.
Procedure
1. The cross-slide is adjusted for required depth of cut and the lathe is switched on.
The plain turning tool mounted on the tolpost is given feed to obtain a part of given diameter
of the collar.
2. The plain turning tool is used to turn a step at the right side of the collar upto the
given length.
3. The above process is repeated until the required diameter is obtained. This is
done by gradually moving the cross-slide after each cut.
4. Straight turning is done at the left side of the collar with the help of a parting tool
to the given diameter and length.
5. During this process, the diameter of the work is checked with the help of outside
caliper and inside caliper.
6. Finishing tool is used to obtain accurate dimensions of length and diameter.
Result
The finished piece of work is sent for inspection after the machining is over.
41
Exercise - 10 (Plain and taper turning)
Operation - 1
Operation - 2
All dimensions are in mm
42
10. PLAIN AND TAPER TURNING
Aim
To perform the operations of plain and taper turning on a cylindrical part of given
dimensions.
Required instruments
1. Facing tool
2. Plain turning tool
3. Chuck key
4. Tool holder
5. Steel rule
6. Vernier caliper
7. Outside caliper
8. Inside caliper
9. Surface gauge
Tool setting
A facing tool, and a plain turning tool are mounted on the toolpost and their cutting
edges are set exactly aligned to the axis of the lathe spindle. The compund rest is set at 0°
mark.
Holding of the work
1. The metal piece to be machined is held in the chuck of the lathe.
2. Surface gauge is used to check whether the work is held aligning with the lathe
axis.
Selection of cutting speed
πdn
Cutting speed = ——— m/min.
1,000
The above formula is used to arrive at a proper cutting speed for machining and the
spindle speed is adjusted suitably.
43
Facing operation
The lathe is switched on and the facing tool mounted on the toolpost is given feed by
the cross-slide perpendicular to the lathe axis. A flat surface on the face of the work is
generated.
Marking
Marking is done on the work at the required point to indicate the length to be plain
turned.
Procedure
1. The cross-slide is adjusted for required depth of cut and the lathe is switched on.
The plain turning tool mounted on the tolpost is given feed by the carriage parallel to the
lathe axis.
2. The above process is repeated until the required diameter is obtained. This is
done by gradually moving the cross-slide after each cut.
3. During this process, the diameter of the work is checked with the help of outside
caliper.
4. Finishing tool is used to obtain accurate dimensions of length and diameter.
5. The angle(Ø) through which the compound slide is to be swiveled is calculated by
the formula
D-d
tan Ø = ---------2l
Where
‘D’ is the larger diameter
‘d’ is the smaller diameter and
‘l’ is the length of the taper
6. After plain turning is done, the compound slide is swiveled to the angle calculated
as above. The plain turning tool mounted on the toolpost is given feed by the compund slide
at the required angle to the lathe axis. The above process is repeated until the taper of
required length is obtained. This is done by adjusting the cross-slide for depth of cut and
compound slide for feed. While doing so, feed is provided from smaller diameter to larger
diameter.
Result
The finished piece of work is sent for inspection after the machining is over.
44
GENERAL MACHINIST
PRACTICAL - II
Note : All the dimensions are given in mm. The size of the M.S. flat is given as 50 x 50 x 6.
The design of the exercises may be modified accoding to the size of the material available.
45
Exercise - 1 (Filing, marking and punching)
Marking and punching
Finished model
All dimensions are in mm
46
1. FILING, MARKING & PUNCHING
Aim
To perform the operations of filing, marking and punching
Tools required
1. Bench vise
2. Try square
3. Hacksaw frame
4. Scriber
5. Steel rule
6. Punches
7. Flat file - rough
8. Flat file - medium
9. Flat file - smooth
10. Triangular file
11. Hammer
12. Divider
13. Chalk paste
14. Vernier caliper
15. Surface plate
Procedure
1. The design of the given model is studied completely to understand the features like
its size and shape.
2. The given piece of metal is checked for sizes whether it is sufficient for the design.
3. Hand tools and measuring instruments are selected suitably to perform the required
operations.
4. The piece of metal (mild steel) is held in the bench vise and two adjacent sides are
filed for squareness using a flat file. These two sides are considered prime sides.
47
48
5. The remaining two sides are also filed for squareness (The angle between adjacent
sides = 90 degrees). The same is checked with the help of a try-square.
6. The piece of work is checked for 90° on all four sides.
7. A thin layer of chalk paste is applied on the flat surface of the metal piece.
8. Chalk is allowed to dry.
9. The given design is scribed on the chalked surface using steel rule, divider and
scriber.
10. Punch marks are made at required points on the surface using a dot punch and a
hammer.
11. Punch marks are made by keeping the punch inclined at 60° so that they are filed
off later.
12.The spacing between adjacent punch marks should be atleast 6mm.
Result
The operations of square filing, marking and punching are performed according to
the given design on the given M.S plate.
49
Exercise - 2 (‘
’ cutting)
Marking and punching
Finished model
All dimensions are in mm
50
2. ‘
’ CUTTING
Aim
To make the given shape in given size on the given M.S. plate.
Tools required
1. Bench vise
2. Try square
3. Hacksaw frame
4. Scriber
5. Steel rule
6. Punches
7. Flat file - rough
8. Flat file - medium
9. Flat file - smooth
10. Triangular file
11. Hammer
12. Divider
13. Chalk paste
14. Vernier caliper
15. Surface plate
Procedure
1. The design of the given model is studied completely to understand the features like
its size and shape.
2. The given piece of metal is checked for sizes whether it is sufficient for the design.
3. Hand tools and measuring instruments are selected suitably to perform the required
operations.
4. The piece of metal (mild steel) is held in the bench vise and two adjacent sides are
filed for squareness using a flat file. These two sides are considered prime sides.
51
52
5. The remaining two sides are also filed for squareness (The angle between adjacent
sides = 90 degrees). The same is checked with the help of a try-square.
6. The piece of work is checked for 90° on all four sides.
7. A thin layer of chalk paste is applied on the flat surface of the metal piece.
8. Chalk is allowed to dry.
9. Steel rule, divider and scriber are used for scribing.
10. The given design is scribed on the chalked surface by a scriber
11. Punch marks are made at required points on the surface using a dot punch .
12. Punch marks are made by keeping the punch inclined at 60° so that they are filed
off later.
13. The spacing between adjacent punch marks should be at least 6mm.
14. Thin auxiliary lines are made at a distance of 1.5mm from the punched line.
15. Hack cuts are made on these auxiliary lines. The unwanted portion of the metal
piece is removed.
16. The remaining portion of the metal piece is filed with the help of flat files (rough,
medium and smooth)
17. When filing, care is taken that half of the punch mark is retained on the workpiece.
18. The sharp corners of the shape are finish filed with the help of triangular file.
19. The edge surfaces of the workpiece are checked frequently for perpendicularity
and parallelism with the help of a try-square.
Conclusion
The operations of square filing, marking, punching, hacksaw cutting and finish filing
(for ‘T’ shape) are performed according to the given design on the given M.S plate.
53
Exercise - 3 (‘
’ cutting)
Marking and punching
Finished model
All dimensions are in mm
54
3. ‘
’ CUTTING
Aim
To make the given shape in given size on the given M.S. plate.
Tools required
1. Bench vise
2. Try square
3. Hacksaw frame
4. Scriber
5. Steel rule
6. Punches
7. Flat file - rough
8. Flat file - medium
9. Flat file - smooth
10. Triangular file
11. Hammer
12. Divider
13. Chalk paste
14. Vernier caliper
15. Surface plate
Procedure
1. The design of the given model is studied completely to understand the features like
its size and shape.
2. The given piece of metal is checked for sizes whether it is sufficient for the design.
3. Hand tools and measuring instruments are selected suitably to perform the required
operations.
4. The piece of metal (mild steel) is held in the bench vise and two adjacent sides are
filed for squareness using a flat file. These two sides are considered prime sides.
55
56
5. The remaining two sides are also filed for squareness (The angle between adjacent
sides = 90 degrees). The same is checked with the help of a try-square.
6. The piece of work is checked for 90° on all four sides.
7. A thin layer of chalk paste is applied on the flat surface of the metal piece.
8. Chalk is allowed to dry.
9. Steel rule, divider and scriber are used for scribing.
10. The given design is scribed on the chalked surface by a scriber
11. Punch marks are made at required points on the surface using a dot punch .
12. Punch marks are made by keeping the punch inclined at 60° so that they are filed
off later.
13. The spacing between adjacent punch marks should be at least 6mm.
14. Thin auxiliary lines are made at a distance of 1.5mm from the punched line.
15. Hack cuts are made on these auxiliary lines. The unwanted portion of the metal
piece is removed.
16. The remaining portion of the metal piece is filed with the help of flat files (rough,
medium and smooth)
17. When filing, care is taken that half of the punch mark is retained on the workpiece.
18. The sharp corners of the shape are finish filed with the help of triangular file.
19. The edge surfaces of the workpiece are checked frequently for perpendicularity
and parallelism with the help of a try-square.
Conclusion
The operations of square filing, marking, punching, hacksaw cutting and finish filing
(for ‘T’ shape) are performed according to the given design on the given M.S plate.
57
Exercise - 4 (‘
’ cutting)
Marking and punching
Finished model
All dimensions are in mm
58
4. ‘
’ CUTTING
Aim
To make the given shape in given size on the given M.S. plate.
Tools required
1. Bench vise
2. Try square
3. Hacksaw frame
4. Scriber
5. Steel rule
6. Punches
7. Flat file - rough
8. Flat file - medium
9. Flat file - smooth
10. Triangular file
11. Hammer
12. Divider
13. Chalk paste
14. Vernier caliper
15. Bevel protractor
16. Protractor
17. Combination set
18. Surface plate
Procedure
1. The design of the given model is studied completely to understand the features like
its size and shape.
2. The given piece of metal is checked for sizes whether it is sufficient for the design.
3. Hand tools and measuring instruments are selected suitably to perform the required
operations.
59
60
4. The piece of metal (mild steel) is held in the bench vise and two adjacent sides are
filed for squareness using a flat file. These two sides are considered prime sides.
5. The remaining two sides are also filed for squareness (The angle between adjacent
sides = 90 degrees). The same is checked with the help of a try-square.
6. The piece of work is checked for 90° on all four sides.
7. A thin layer of chalk paste is applied on the flat surface of the metal piece.
8. Chalk is allowed to dry.
9. Steel rule, divider and scriber are used for scribing.
10. The given design is scribed on the chalked surface by a scriber. The angular lines
are scribed with the help of a protractor head of a combination set.
11. Punch marks are made at required points on the surface using a dot punch .
12. Punch marks are made by keeping the punch inclined at 60° so that they are filed
off later.
13. The spacing between adjacent punch marks should be at least 6mm.
14. Thin auxiliary lines are made at a distance of 1.5mm from the punched line.
15. Hack cuts are made on these auxiliary lines. The unwanted portion of the metal
piece is removed.
16. The remaining portion of the metal piece is filed with the help of flat files (rough,
medium and smooth)
17. When filing, care is taken that half of the punch mark is retained on the workpiece.
18. The sharp corners of the shape are finish filed with the help of triangular file.
19. The edge surfaces of the workpiece are checked frequently for perpendicularity
and parallelism with the help of a try-square.
Conclusion
The operations of square filing, marking, punching, hacksaw cutting and finish filing
(for ‘T’ shape) are performed according to the given design on the given M.S plate.
61
Exercise - 5 (‘
’ cutting)
Marking and punching
Finished model
All dimensions are in mm
62
5. ‘
’ CUTTING
Aim
To make the given shape in given size on the given M.S. plate.
Tools required
1. Bench vise
2. Try square
3. Hacksaw frame
4. Scriber
5. Steel rule
6. Punches
7. Flat file - rough
8. Flat file - medium
9. Flat file - smooth
10. Triangular file
11. Hammer
12. Divider
13. Chalk paste
14. Vernier caliper
15. Bevel protractor
16. Protractor
17. Combination set
18. Surface plate
Procedure
1. The design of the given model is studied completely to understand the features like
its size and shape.
2. The given piece of metal is checked for sizes whether it is sufficient for the design.
3. Hand tools and measuring instruments are selected suitably to perform the required
operations.
63
64
4. The piece of metal (mild steel) is held in the bench vise and two adjacent sides are
filed for squareness using a flat file. These two sides are considered prime sides.
5. The remaining two sides are also filed for squareness (The angle between adjacent
sides = 90 degrees). The same is checked with the help of a try-square.
6. The piece of work is checked for 90° on all four sides.
7. A thin layer of chalk paste is applied on the flat surface of the metal piece.
8. Chalk is allowed to dry.
9. Steel rule, divider and scriber are used for scribing.
10. The given design is scribed on the chalked surface by a scriber. The angular lines
are scribed with the help of a protractor head of a combination set.
11. Punch marks are made at required points on the surface using a dot punch .
12. Punch marks are made by keeping the punch inclined at 60° so that they are filed
off later.
13. The spacing between adjacent punch marks should be at least 6mm.
14. Thin auxiliary lines are made at a distance of 1.5mm from the punched line.
15. Hack cuts are made on these auxiliary lines. The unwanted portion of the metal
piece is removed.
16. The remaining portion of the metal piece is filed with the help of flat files (rough,
medium and smooth)
17. When filing, care is taken that half of the punch mark is retained on the workpiece.
18. The sharp corners of the shape are finish filed with the help of triangular file.
19. The edge surfaces of the workpiece are checked frequently for perpendicularity
and parallelism with the help of a try-square.
Conclusion
The operations of square filing, marking, punching, hacksaw cutting and finish filing
(for ‘T’ shape) are performed according to the given design on the given M.S plate.
65
Exercise - 6 (‘
’ cutting)
Marking and punching
Finished model
All dimensions are in mm
66
6. ‘
’ CUTTING
Aim
To make the given shape in given size on the given M.S. plate.
Tools required
1. Bench vise
2. Try square
3. Hacksaw frame
4. Scriber
5. Steel rule
6. Punches
7. Flat file - rough
8. Flat file - medium
9. Flat file - smooth
10. Triangular file
11. Hammer
12. Divider
13. Chalk paste
14. Vernier caliper
15. Bevel protractor
16. Protractor
17. Combination set
18. Surface plate
Procedure
1. The design of the given model is studied completely to understand the features like
its size and shape.
2. The given piece of metal is checked for sizes whether it is sufficient for the design.
3. Hand tools and measuring instruments are selected suitably to perform the required
operations.
67
68
4. The piece of metal (mild steel) is held in the bench vise and two adjacent sides are
filed for squareness using a flat file. These two sides are considered prime sides.
5. The remaining two sides are also filed for squareness (The angle between adjacent
sides = 90 degrees). The same is checked with the help of a try-square.
6. The piece of work is checked for 90° on all four sides.
7. A thin layer of chalk paste is applied on the flat surface of the metal piece.
8. Chalk is allowed to dry.
9. Steel rule, divider and scriber are used for scribing.
10. The given design is scribed on the chalked surface by a scriber. The angular lines
are scribed with the help of a protractor head of a combination set.
11. Punch marks are made at required points on the surface using a dot punch .
12. Punch marks are made by keeping the punch inclined at 60° so that they are filed
off later.
13. The spacing between adjacent punch marks should be at least 6mm.
14. Thin auxiliary lines are made at a distance of 1.5mm from the punched line.
15. Hack cuts are made on these auxiliary lines. The unwanted portion of the metal
piece is removed.
16. The remaining portion of the metal piece is filed with the help of flat files (rough,
medium and smooth)
17. When filing, care is taken that half of the punch mark is retained on the workpiece.
18. The sharp corners of the shape are finish filed with the help of triangular file.
19. The edge surfaces of the workpiece are checked frequently for perpendicularity
and parallelism with the help of a try-square.
Conclusion
The operations of square filing, marking, punching, hacksaw cutting and finish filing
(for ‘T’ shape) are performed according to the given design on the given M.S plate.
69
Exercise - 7 (‘
’ cutting)
Marking and punching
Finished model
All dimensions are in mm
70
7. ‘
’ CUTTING
Aim
To make the given shape in given size on the given M.S. plate.
Tools required
1. Bench vise
2. Try square
3. Hacksaw frame
4. Scriber
5. Steel rule
6. Punches
7. Flat file - rough
8. Flat file - medium
9. Flat file - smooth
10. Triangular file
11. Hammer
12. Divider
13. Chalk paste
14. Vernier caliper
15. Bevel protractor
16. Protractor
17. Combination set
18. Surface plate
Procedure
1. The design of the given model is studied completely to understand the features like
its size and shape.
2. The given piece of metal is checked for sizes whether it is sufficient for the design.
3. Hand tools and measuring instruments are selected suitably to perform the required
operations.
71
72
4. The piece of metal (mild steel) is held in the bench vise and two adjacent sides are
filed for squareness using a flat file. These two sides are considered prime sides.
5. The remaining two sides are also filed for squareness (The angle between adjacent
sides = 90 degrees). The same is checked with the help of a try-square.
6. The piece of work is checked for 90° on all four sides.
7. A thin layer of chalk paste is applied on the flat surface of the metal piece.
8. Chalk is allowed to dry.
9. Steel rule, divider and scriber are used for scribing.
10. The given design is scribed on the chalked surface by a scriber. The angular lines
are scribed with the help of a protractor head of a combination set.
11. Punch marks are made at required points on the surface using a dot punch .
12. Punch marks are made by keeping the punch inclined at 60° so that they are filed
off later.
13. The spacing between adjacent punch marks should be at least 6mm.
14. Thin auxiliary lines are made at a distance of 1.5mm from the punched line.
15. Hack cuts are made on these auxiliary lines. The unwanted portion of the metal
piece is removed.
16. The remaining portion of the metal piece is filed with the help of flat files (rough,
medium and smooth)
17. When filing, care is taken that half of the punch mark is retained on the workpiece.
18. The sharp corners of the shape are finish filed with the help of triangular file.
19. The edge surfaces of the workpiece are checked frequently for perpendicularity
and parallelism with the help of a try-square.
Conclusion
The operations of square filing, marking, punching, hacksaw cutting and finish filing
(for ‘T’ shape) are performed according to the given design on the given M.S plate.
73
Exercise - 8 (‘
’ cutting)
Marking and punching
Finished model
All dimensions are in mm
74
8. ‘
’ CUTTING
Aim
To make the given shape in given size on the given M.S. plate.
Tools required
1. Bench vise
2. Try square
3. Hacksaw frame
4. Scriber
5. Steel rule
6. Punches
7. Flat file - rough
8. Flat file - medium
9. Flat file - smooth
10. Triangular file
11. Hammer
12. Divider
13. Chalk paste
14. Vernier caliper
15. Bevel protractor
16. Protractor
17. Combination set
18. Surface plate
Procedure
1. The design of the given model is studied completely to understand the features like
its size and shape.
2. The given piece of metal is checked for sizes whether it is sufficient for the design.
3. Hand tools and measuring instruments are selected suitably to perform the required
operations.
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4. The piece of metal (mild steel) is held in the bench vise and two adjacent sides are
filed for squareness using a flat file. These two sides are considered prime sides.
5. The remaining two sides are also filed for squareness (The angle between adjacent
sides = 90 degrees). The same is checked with the help of a try-square.
6. The piece of work is checked for 90° on all four sides.
7. A thin layer of chalk paste is applied on the flat surface of the metal piece.
8. Chalk is allowed to dry.
9. Steel rule, divider and scriber are used for scribing.
10. The given design is scribed on the chalked surface by a scriber. The angular lines
are scribed with the help of a protractor head of a combination set.
11. Punch marks are made at required points on the surface using a dot punch .
12. Punch marks are made by keeping the punch inclined at 60° so that they are filed
off later.
13. The spacing between adjacent punch marks should be at least 6mm.
14. Thin auxiliary lines are made at a distance of 1.5mm from the punched line.
15. Hack cuts are made on these auxiliary lines. The unwanted portion of the metal
piece is removed.
16. The remaining portion of the metal piece is filed with the help of flat files (rough,
medium and smooth)
17. When filing, care is taken that half of the punch mark is retained on the workpiece.
18. The sharp corners of the shape are finish filed with the help of triangular file.
19. The edge surfaces of the workpiece are checked frequently for perpendicularity
and parallelism with the help of a try-square.
Conclusion
The operations of square filing, marking, punching, hacksaw cutting and finish filing
(for ‘T’ shape) are performed according to the given design on the given M.S plate.
77
Exercise - 9 (‘
’ cutting)
Marking and punching
Finished model
All dimensions are in mm
78
9. ‘
’ CUTTING
Aim
To make the given shape in given size on the given M.S. plate.
Tools required
1. Bench vise
2. Try square
3. Hacksaw frame
4. Scriber
5. Steel rule
6. Punches
7. Flat file - rough
8. Flat file - medium
9. Flat file - smooth
10. Triangular file
11. Hammer
12. Divider
13. Chalk paste
14. Vernier caliper
15. Bevel protractor
16. Protractor
17. Combination set
18. Surface plate
Procedure
1. The design of the given model is studied completely to understand the features like
its size and shape.
2. The given piece of metal is checked for sizes whether it is sufficient for the design.
3. Hand tools and measuring instruments are selected suitably to perform the required
operations.
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80
4. The piece of metal (mild steel) is held in the bench vise and two adjacent sides are
filed for squareness using a flat file. These two sides are considered prime sides.
5. The remaining two sides are also filed for squareness (The angle between adjacent
sides = 90 degrees). The same is checked with the help of a try-square.
6. The piece of work is checked for 90° on all four sides.
7. A thin layer of chalk paste is applied on the flat surface of the metal piece.
8. Chalk is allowed to dry.
9. Steel rule, divider and scriber are used for scribing.
10. The given design is scribed on the chalked surface by a scriber. The angular lines
are scribed with the help of a protractor head of a combination set.
11. Punch marks are made at required points on the surface using a dot punch .
12. Punch marks are made by keeping the punch inclined at 60° so that they are filed
off later.
13. The spacing between adjacent punch marks should be at least 6mm.
14. Thin auxiliary lines are made at a distance of 1.5mm from the punched line.
15. Hack cuts are made on these auxiliary lines. The unwanted portion of the metal
piece is removed.
16. The remaining portion of the metal piece is filed with the help of flat files (rough,
medium and smooth)
17. When filing, care is taken that half of the punch mark is retained on the workpiece.
18. The sharp corners of the shape are finish filed with the help of triangular file.
19. The edge surfaces of the workpiece are checked frequently for perpendicularity
and parallelism with the help of a try-square.
Conclusion
The operations of square filing, marking, punching, hacksaw cutting and finish filing
(for ‘T’ shape) are performed according to the given design on the given M.S plate.
81
Exercise - 10 (‘
’ cutting)
Marking and punching
Finished model
All dimensions are in mm
82
10. ‘
’ CUTTING
Aim
To make the given shape in given size on the given M.S. plate.
Tools required
1. Bench vise
2. Try square
3. Hacksaw frame
4. Scriber
5. Steel rule
6. Punches
7. Flat file - rough
8. Flat file - medium
9. Flat file - smooth
10. Triangular file
11. Hammer
12. Divider
13. Chalk paste
14. Vernier caliper
15. Bevel protractor
16. Protractor
17. Combination set
18. Surface plate
Procedure
1. The design of the given model is studied completely to understand the features like
its size and shape.
2. The given piece of metal is checked for sizes whether it is sufficient for the design.
3. Hand tools and measuring instruments are selected suitably to perform the required
operations.
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4. The piece of metal (mild steel) is held in the bench vise and two adjacent sides are
filed for squareness using a flat file. These two sides are considered prime sides.
5. The remaining two sides are also filed for squareness (The angle between adjacent
sides = 90 degrees). The same is checked with the help of a try-square.
6. The piece of work is checked for 90° on all four sides.
7. A thin layer of chalk paste is applied on the flat surface of the metal piece.
8. Chalk is allowed to dry.
9. Steel rule, divider and scriber are used for scribing.
10. The given design is scribed on the chalked surface by a scriber. The angular lines
are scribed with the help of a protractor head of a combination set.
11. Punch marks are made at required points on the surface using a dot punch .
12. Punch marks are made by keeping the punch inclined at 60° so that they are filed
off later.
13. The spacing between adjacent punch marks should be at least 6mm.
14. Thin auxiliary lines are made at a distance of 1.5mm from the punched line.
15. Hack cuts are made on these auxiliary lines. The unwanted portion of the metal
piece is removed.
16. The remaining portion of the metal piece is filed with the help of flat files (rough,
medium and smooth)
17. When filing, care is taken that half of the punch mark is retained on the workpiece.
18. The sharp corners of the shape are finish filed with the help of triangular file.
19. The edge surfaces of the workpiece are checked frequently for perpendicularity
and parallelism with the help of a try-square.
Conclusion
The operations of square filing, marking, punching, hacksaw cutting and finish filing
(for ‘T’ shape) are performed according to the given design on the given M.S plate.
84