warning if tiese machines are to be used in industry additional

warning if tiese machines are to be used in industry additional
SAFETY NOTES.
ELECTRICAL.
Wotorised Machines.
T h e machine must be connected t o the mains supply via a standard 13A plug and socket.
Fuse ratings are shown on the machine label.
When installing the machine follow the standard connection colour code for 13A plugs,
ensuring that the earth wire (green or green/yellow) is connected correctly, AND that the
socket t o be used has a good earth connection back t o the Electricity Board's earth at the
mains inlet t o the premises. If there is any doubt, consult your local Electricity Authority.
I f electrical maintenance is necessary, SWITCH O F F THE MACHINE AND DISCONNECT
T H E MAINS PLUG BEFORE REMOVING A N Y ELECTRICAL COMPARTMENT OR
CONTROL BOX COVER.
REPLACE A L L COVERS BEFORE RECONNECTING TO THE MAINS SUPPLY.
Unmotorised Machines.
A p p l y the rules above t o your own installation and ensure that A L L electrical connections
are covered t o prevent accidental contact.
Have your installation checked b y a qualified electrician before putting into use.
OPERATING.
All machine operations including tool grinding present a hazard, particularly t o the operator's
eyes. Swarf is sharp and hot, and it can be projected upwards as small, high velocity particles
t h i s occurs particularly when machining brass. Therefore:
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ALWAYS WEAR PROTECTIVE GOGGLES WHEN USING MACHINES DON'T T A K E
CHANCES.
Rotating parts are also a hazard, therefore:
1. Ensure that all work pieces and cutting tools are correctly and adequately secured before
commencing machining and at intervals during prolonged machining operations.
2. Don't make measurements while the work is rotating.
3. Don't judge the finish b y running your fingers along a machined part whilst it is rotating.
4. Don't use hand tools such as files close t o the chuck.
THINK SAFETY.
WARNING
I F T I E S E MACHINES ARE TO BE USED I N INDUSTRY ADDITIONAL GUARDING MAY BE
REWIRED AS DEFINED I N THE FACTORIES ACT 1961 AND THE HEALTH AND SAFFX'Y
AT WRK ACT 1974.
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THE COWELLS 9 0 LATHE
T h e Cowells 90 Lathe is a conventional ,backgeared, screwcutting centre lathe.
T h i s Manual outlines its maintenance and operation and provides an introduction t o the Centre
L a t h e for the novice and is also applicable t o the 90 CW and 90 HS Lathes. The user's attention
is directed t o the 'Cowells 9 0 Lathe Handbook' (code 10-260) which provides further and more
detailed descriptions o f the machine and its application t o a wide range o f machining operations.
SECTION 1
MACHINE PARTS A N D THEIR FUNCTIONS.
Movements.
All movements affecting the cutting tool positions, including drilling, etc., using the tailstock
a r e controlled by feedscrews and graduated handwheels. Note that the CW Lathe tailstock
is lever operated. A l l the feedscrews have a pitch o f I m m and the handwheels 4 0
divisions. Therefore, one full rotation o f the handwheel will produce a corresponding linear
movement o f the associated slide o f 1mm and a rotation o f one division will produce a
movement o f .025 mm (.001" approx.) NOTE : A l l feeds with the exception o f the cross
slide are direct reading, i.e. the handwheel dial indicates directly the length turned o n the
d e p t h o f the hole drilled.
W i t h the cross slide, however, the handwheel dial indicates the depth o f cut, BUT, if the t o e l
i s moved inwards one division LO25 mm) the diameter o f the work will be reduced by MI ICE
t h a t amount (.05 mm). THIS IMPORTANT FACTOR MUST BE REMEMBERED WHEN
T U R N I N G DIAMETERS.
T w o additional 'preset' movements are provided a t the Compound Slide and Tailstock t o
facilitate angle and taper turning.
Compound Slide.
T h e Compound Slide operates o n a rotatable base secured to the cross slide b y t w o angle
pins and screws, thus allowing the slide t o be set at various angles t o the lathe axis for taper
a n d angle turning.
To set the compound slide angle, slacken the t w o screws o n the side faces o f the cross slide
immediately under the compound slide. The compound slide can then be rotated t o the
required angle using the angular scale o n the cross slide face. Tighten the screws.
NOTE: Some accessories are attached t o the cross slide using the compound slide mounting
hole. For these accessories t o be used the compound slide and its base must be removed as
a complete unit.
To remove the compound slide assembly, remove the t w o screws t o allow the angle pins t o
move outwards. Then, rotate the unit back and forth, pulling upwards t o push the pins clear.
Note that the assembly is a tight fit and some force is required t o remove it.
Tailstock Set Over.
The tailstock centre can be moved o u t o f alignment w i t h the lathe centre line t o enable taper
turning to be carried out. The total movement is limited t o 6mm and this method o f taper
turning is normally restricted t o very small angles.
T o set the tailstock over:
a) Release the clamp lever at the rear o f the tailstock body.
b) Using the t w o screws (one at the front, and one a t the back o f the tailstock body) move
the body sideways o n its base alternately slackening one screw and tightening the
other u n t i l the desired amount o f set over, in the desired direction, is obtained. The tailstock
can then be used i n the normal way except that the parts turned will have a taper i n
diameter equal t o twice the amount o f set over.
T o set the tailstock back t o its centre position repeat the operations i n (a) and (b) b u t i n
2
t h e reverse direction, using a test bar and dial test indicator t o obtain accurate alignment.
Alternatively, alignment can be set by turning the ends of a bar between centres t o check
t h e setting. The setting is correct when the diameter obtained at each end o f the bar is the
same FOR THE SAME TOOL SETTING.
D r i v e Systems.
1.CW A N D HS LATHES
Single pulley and thyristor speed controller.
2 . 9 0 LATHE
T h e headstock spindle is driven b y a conventional 3 step pulley arrangement from a counters h a f t powered b y the motor. Belt tensioning is achieved b y means o f a cam operating o n a
c a m follower screw which projects through the countershaft bracket. Pulling the cam lever
forward releases the belt tension thus enabling the various steps o f the pulley system t o be
selected. Pushing the lever back tensions the belt.
--
Backgear.
T h e backgear is a device used t o extend the speed range o f the headstock spindle by introducing
gearing between the driven pulley and the spindle.
W i t h the 3 step pulley, 6 speeds can be selected as follows:
a) Unqeared.
Disengage the backgear b y releasing the grubscrew in the t o p face at the rear o f the headstock
casting. Push the lever on the backgear eccentric back until the gears are disengaged. Tighten
t h e screw. Secure the 3 step pulley t o the spindle b y tightening the grubscrew i n the centre
'Vee' o f the pulley. The machine is n o w in direct drive and the 3 speeds available are 880,
5 0 0 and 280 r.p.m.
N O T E : These speeds apply t o 5 0 Hz machines. For 6 0 Hz machines the speeds w i l l be
approximately 20% higher.
b) Geared.
Reverse the procedure in (a) t o engage the backgear ensuring that there is a small amount o f
clearance between the gear teeth. Never run gears tightly meshed. Remember t o secure the
backgear eccentric locking screw and release the pulley locking screw. The machine is n o w
in geared drive and the speeds at the pulley are reduced b y a ratio o f 4.6 t o 1giving 180, 107
a n d 6 0 r.p.m. at the spindle (50 Hz machine).
A u t o Traverse and Clutch. (90 Lathe only).
A u t o traverse provides a means o f moving the cutting tool along the axis o f the lathe t o
perform turning operations automatically. It is achieved b y driving the leadscrew through
a series o f gears driven from the headstock spindle, the rate o f movement (feed) being
determined b y the gear ratio and the pitch o f the leadscrew. Note that 'feed' is the term
used t o express the movement along the axis f o r each revolution o f the workpiece and is
constant f o r any given gear ratio regardless o f spindle speed. The gearing fitted for the auto
traverse provides a feed o f .07mm (.003") approx.
T h e direction o f traverse is controlled by the total number o f gears in the 'train' which is
arranged t o give movement t o the left o r right. Movement t o the left (toward the headstock)
is normal.
The gears are fitted t o a slotted plate clamped to a boss at the headstock end o f the lathe.
The slot in the plate allows for variations in gear centres iflwhen the ratio is changed, and
t h e whole plate, complete w i t h gears, may be rotated around its mounting boss t o engage
t h e driving gear o n the tailend of the headstock spindle. As with all gears, leave a small
clearance between the teeth when setting.
The leadscrew is connected t o the gear system through a clutch operated by the lever at the
front o f the headstock. Moving the lever t o the left disengages the drive, t o the right engages
the drive.
A t r i p bar is provided t o disengage the clutch automatically as the t o o l approaches t h e headstock. The t r i p is in the form o f a slotted bar mounted o n the 'apron' a t the front of the
saddle, the slot allowing for adjustment of the precise point o f trip. For instance, t h e trip
3
can be set to disengage the clutch when the cutting tool is about 118" from the chuck jaws.
Then long turning operations can be performed automatically, each successive cut stopping
at the same point without the risk of the tool or chuck being damaged should the operator's
attention be elsewhere.
Screwcutting: (90 Lathe Only)
The system of driving the leadscrew through a train of gears is also used for screw cutting.
For this the gears are selected from the range provided in accessory set 10-206 together with
those provided with the auto-traverse, t o give the required rate of movement, but in this case
t h e feed is equal to the pitch of the thread to be cut. When screwcutting, the clutch is NOT
disengaged at the end of each cut. The machine MUST BE STOPPED, THE TOOL WITHDRAWN
A N D TRAVERSED BACK TO THE START OF THE THREAD USING THE MOTOR REVERSE.
The tool is then set back to i t s previous position plus the amount for the next cut and the
operation repeated until the required depth of thread is achieved.
SECTION 2
CARE OF THE MACHINE.
Lubrication.
Oiling points are provided for the headstock and leadscrew bearings. All other working
surfaces such as slides, feedscrews, gears etc., are lubricated by applying oil directly to the
surface. Use a good quality SAE 20 or 30 grade of machine oil such as Myford NUTB,
for all lubrication. Do not use 'sewing machine' type oils of the 3 in 1 kind. These are
for light duty only and are not suitable for the Cowells machine.
Frequency of lubrication is dependent upon the duty of the machine but:
(a) Always lubricate before use and after cleaning down.
(b) During prolonged machining operations lubricate at regular intervals paying particular
attention to the headstock oil cups.
Adjustment.
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1. Gib Strip2
Gib strips are steel inserts fitted between the faces of sliding parts to provide accurate control
of the fit of the parts, thus allowing for initial setting and compensation for wear. They are
positioned and secured by means of screws and locknuts and are used on the compound slide,
cross slide and saddle. To adjust any of the gib strips, slacken the appropriate locknuts and
then set each screw in turn to achieve a good slide action, without sideplay and without undue
loading of the feedscrew. Tighten the locknut as each screw is set to ensure that there will be
no further movement when the effect of the setting is checked. Readjust each screw if necessary
t o achieve a good slide action for the whole of the travel.
2. Feedscrew Backlash.
Feedscrew backlash is controlled by the position of the handwheel on the feedscrew extension.
To adjust, slacken the screw in the side of the handwheel and then turn the slotted screw in
the front of the handwheel clockwise until the backlash i s 5 divisions or less of the graduations.
Tighten the screw in the side of the handwheel.
Note that it is impossible to eliminate backlash completely and that any backlash is always
accounted for when performing machining operations.
3. Headstock Spindle Bearings (90 Lathe).
HS Lathe has sealed ball bearings, no adjustment.
CW Lathe has taper cone bearings. Adjustment is provided at the rear cone.
90 Lathe adjustment is provided by means of split caps and screws. To adjust, top up the
bearing cups with the correct oil, set the bzlt to give the highest speed (880 r.p.m.) and switch
the machine on. After a few minutes, switch off and release the belt tension. Turn the bearing
cap screws very slowly and a fraction of a turn a t a time, clockwise to tighten the bearing
whilst rotating the spindle back and forth by hand. The correct setting i s when the screws
are as far clockwise as they can be set without there being any drag on the spindle.
4. Headstock Spindle End Float.
I f end float adjustment is necessary, slacken the grubscrew securing the large gearwheel t o
t h e spindle at the end o f the headstock. Turn the screw collar immediately behind the gear
clockwise (viewed from the rear) t o reduce end float. Tighten the gear wheel securing screw.
T h e setting should be sufficient t o remove end float only; there should be n o loading o f the
bearing faces.
5. Belt Tension.
If adjustment of the belt (or belts) tension becomes necessary, proceed as follows:
a) Position the belt o n the centre step o f the 3 step pulley.
b) Slacken the locknut o n the cam follower screw at the rear o f the countershaft bracket
( o n the 10-200B also slacken the t w o screws o n the right hand face o f the motor compartment.)
c) Set the cam lever t o the tensioned position and adjust the cam follower screw t o obtain t h e
correct belt tension; tighten the locknut.
d) 10-2008 only. After (c) above, push down on the screw in the slot in the motor compartment, (b) above, t o tension the motor drive belt. Tighten both screws o n the right hand face
o f the motor compartment.
T h e setting is now correct for all 3 steps of the spindle pulley.
C W and HS Lathe belts are tensioned b y adjusting the motor position.
General Rules.
1. Pay attention t o lubrication at all times.
2. Keep working surfaces clear of swarf as much as possible. Swarf is abrasive and in some
cases can absorb oil, resulting in 'drying out' o f a previously lubricated surface.
3. Always clean the machine, re-oil after use, particularly if water soluble oils or paraffin
have been used as cutting lubricants. These products can cause rust.
4. Do n o t use abrasive fluids (metal polish etc.,) t o clean the machine. Remove any swarf
w i t h a soft brush wipe with a clean d r y cloth and re-oil.
5. Never leave the machine unused for long periods w i t h the belts tensioned. Always release
t h e belt tension a t the end o f working period.
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N O T E : These rules should also be applied t o machine accessories.
SECTION 3
OPERATING T H E MACHINE
W O R K HOLDING A N D SUPPORT
Centres
Rotating Centre
Between Centres.
This is the simplest method of work holding and consists o f drilling a centre hole using a
centre drill, in each end o f the material. These are then used t o support the material o n t h e
centres i n the headstock and tailstock. Note that the hard centre is fitted t o the tailstock
a n d the soft centre t o the headstock. Rotary motion is imparted by means o f a 'carrier'
or 'dog' which is clamped t o the work a t the headstock end and is driven b y a peg fitted t o
t h e faceplate. Note that the tailstock centre must be kept well lubricated and that, as turning
progresses, the heat generated will cause t h e work t o expand. This necessitates readjusting
t h e tailstock centre at intervals t o compensate for the expansion.
F o u r Jaw Chucks.
Independent 4 Jaw Chuck
T h i s is the most versatile type o f chuck. It is possible t o hold irregular shaped articles, such
as castings and square bar and give absolute accuracy when holding round work. The Jaws
c a n be reversed t o hold large objects, or just one or t w o can be reversed and the others left
in their normal position when, for instance, rectangular objects need t o be held. T o reverse
t h e jaws, withdraw them completely and remove the screw from its recessed tongue seating
on the jaw. Turn the jaw over, refit t o the screw and replace the chuck. The method o f
setting the chuck is t o open each jaw i n t u r n until the work will enter. Now tighten each
j a w equally. Rotate the chuck by hand; any major error i n t r u t h will be very obvious and
c a n be corrected by loosening the jaw on the low side as near as can be estimated b y the half
error. The opposite jaw is then tightened to take u p the slack. Note that it may be necessary
to loosen the other jaws slightly t o enable the workpiece t o move. The final setting is done
using a dial test indicator.
There are many indicators o n the market and we suggest that a l o w cost type such as the
Verdict Junior is obtained. They are very robust and o f a size easily managed o n the Lathe.
To use : F i t the indicator i n the toolpost using a bar t o hold it in a convenient position. Set
t h e stylus o f the indicator against the work t o a point where the hand registers a m i d point
on the scale. Now, b y turning the chuck u n t i l one o f the jaws is directly i n line with the
stylus, note the reading o f the dial. Without altering the position o f the indicator turn the
chuck u n t i l the jaw opposite the one just checked is i n line with the stylus; the dial will indicate
error. This can be corrected by loosening one jaw, the low reading one, and tightening the
high reading one until the readings are the same for both jaw positions. Turn your attention
to the other jaws and repeat the process until the work runs true.
It takes practice t o use the 4 Jaw chuck t o the best advantage, b u t once you have gained the
skill i n adjusting the jaws, it takes very little time t o set a job i n it.
The Three Jaw Self Centering Chuck.
This is useful for holding round and hexagonal material. It is quick and easy t o operate and
is favoured by many users. Its main disadvantage is that it is rarely accurate, and error of
0.075mm (.003") is usual, even when new, and the error can vary o n different diameters o f
workpieces. This does n o t detract f r o m the usefulness o f this accessory as long as the user
is aware o f its limitations.
A l l 3 jaw chucks can be used as 'outside' jaw o r 'inside' jaw chucks. This is achieved o n larger
chucks b y having t w o sets o f jaws. O n the Cowells chuck Part No. 10-208 changing f r o m one
mode to the other is done by removing the slotted screw i n the centre o f each jaw, reversing
t h e jaws o n their carriers and securing them with the screws.
3 Jaw Scroll Chuck
Cowells 3 Jaw Scroll Chuck
O t h e r chucks have jaws which can be reversed. In this case when the jaws have been completely
removed, rotate the scroll until the thread is in position t o engage the teeth o f the jaw No.1.
in slot No.1.
N o t e that the jaws are used in the same slots, i.e. No.1. in slot No.1. and so on. If this sequence
is not followed the jaws w i l l not run true.
Faceplate.
--
This is used f o r objects which are t o o awkward t o hold in the chucks, or discs which cannot
be swung over the bed. The work is clamped t o the faceplate using nuts, screws and clamp
plates.
Collets.
Collet Adaptor w i t h Collets
Collets are used t o hold round material which is reasonably accurate in size, but they w i l l
only hold t h e size o f material for which they are bored. Their advantage is that they are
accurate, easy t o use and are particularly useful for repetitive and small diameter work.
Maintain scrupulous cleanliness at all times w i t h collets. Wipe the nose socket clean of chips
a n d swarf before inserting the collet. D o n o t tighten until you have pushed the material into
t h e collet. Atways wipe the material clean and check that there are no burrs marring the
surface as any defects can result i n inaccuracy.
B l a n k collets are available which users can finish t o their own requirements.
W o r k Holdina on the Cross Slide.
So far, the methods o f work holding have been concerned with turning, that is, the technique
where the work is rotated and the tool is moved along or across it.
Angle Plate
Vertical Milling Slide
Machine Vice
T h e alternative t o this is t o have the work clamped t o the cross slide b y means o f various
accessories, then carrying o u t the machining operation b y traversing the work across o r
along a rotating cutter. This method is used for milling on the lathe, the milling cutter being
held i n a chuck. Note that for milling it is normal t o use a vertical slide mounted o n the
cross slide t o give the 3 r d axis o f movement necessary for this operation, the work being
clamped t o the vertical slide.
Fixed (3 Point) Steady,
--This is a device having 3 arms which are used t o support long workpieces whilst machining
operations are performed o n the free end. It is fitted i n the lathe bed slot and is used b y
adjusting the bearing arms t o the diameter o f the work (this is best done w i t h the work held
in a chuck and the steady positioned as close to the chuck as possible). After setting, it can be
moved t o the required position t o support the work and clamped i n the slot in the lathe bed.
Note that the bearing arms must be kept lubricated when i n use.
Travelling Steady.
T h i s is a similar device t o the fixed steady b u t has only t w o arms and is mounted o n the lathe
saddle. It is designed t o travel along the w o r k as machining is carried o u t thus providing a
support immediately above and behind the t o o l when cutting slender workpieces.
N o t e that lubrication is necessary when in use and that the arms must be readjusted after each
cut.
Fixed Steady
Travelling Steady.
TOOLS, SPEEDS A N D MATERIALS.
Tools.
All turning tools have t w o basic requirements t o their shape. These are:
1) Clearance: This is the slope downwards and back from the cutting edge and is applied
at the f r o n t and side (both sides i n some cases e.g. a parting o f f tool). Normal clearance
is between 3 O and 1OO.
2) Top Rake. This is the slope o f the t o p face o f the t o o l and is applied downwards and away
f r o m the cutting edge. The amount o f t o p rake is DEPENDENT O N THE M A T E R I A L T O
BE CUT and can range from zero t o 20' or more.
T h e included angle made b y the clearance and the t o p rake is called the cutting angle.
A range o f preground tools for various types o f operation is listed i n our catalogue;
alternatively, they may be ground from tool steel blanks which are normally available f r o m
t o o l stockists i n various lengths and sizes. The correct size for Cowells machines is %'*
(fjmm) square or smaller.
T o o l Sharpening.
High speed and carbon steel tool bits can be sharpened o n a standard carborundum wheel.
Take care n o t t o burn the tool, especially a t the tip, b y prolonged grinding without cooling.
Tipped tools are ground on a 'green grit' wheel especially made f o r this purpose.
Safety Note.
1) Use o n l y a proprietory manufactured grinder. D o n o t 'lash up' your own. Excessive wheel
speeds can be lethal.
2) A l l grinding should be carried o u t o n the FRONT o f the wheel. NEVER use the sides.
3) Wear protective goggles a t all times.
Tool Setting,
The cutting edge of the t o o l must be set exactly a t the centre height o f the lathe using shims
i f necessary to achieve the correct height and must be firmly clamped with a minimum overhang to prevent deflection due to the cutting load. The position of the tool relative to the
lathe axis is dependent on the type of tool to be used and the work to be done. Normally
the tool is fixed at 90° t o the lathe axis but this can be varied to suit particular requirement,
e.g. when facing.
Speeds.
-The cutting speed for a given material is the speed a t which the surface being cut passes the
tool and is expressed in feet per minute. From this it can be seen that for a given material
cutting speed, as the diameter increases the lathe speed (RPM) must be decreased and
conversely as the diameter decreases the RPM must be increased.
I n theory this requires an infinitely variable control of spindle speed without the loss of
torque a t low speeds. This is not normally available on small lathes which are generally
provided with stepped speeds. In practice therefore it is necessary to compromise and
select the nearest speed (preferably lower) to the ideal speed and generally speeds can be
described as 'slow', 'medium' or 'fast', some variation being allowable around these terms
because of the relationship between the type of material and i t s diameter. When in doubt
start with a low speed and work up.
Applications.
Cast Iron.
1) Slow Speed.
2 ) No top rake on tool (preferably use a tungsten carbide tipped tool).
3 ) Do not use a cutting lubricant.
Mild Steel.
1) Medium speeds.
2 ) Medium to large top rake on tool.
3 ) Use cutting lubricant.
Brass.
1) High speeds.
2) No top rake on tool.
3) Do not use cutting lubricant.
Bronze.
1) Medium to high speeds.
2)Top rake on tool, depending on copper content.
3 ) Cutting lubricant may be required depending on copper content.
Light Alloys.
--1) High speeds.
2) Large top rake on tool.
3 ) Use paraffin as cutting lubricant.
-Castings.
All castings have a hard skin and it is recommended that the first cuts are made with a tipped
tool at a slow speed. When the skin has been removed normal speeds and tools for the material
can be applied.
General Notes on Turning,
1) Feed the tool along the work smoothly using both hands. Variations in feed will be evident
as rings around the work.
2)Use the appropriate cutting lubricant wherever possible. This will produce a better finish
and prolong the tool life.
3)Wherever possible avoid using sharp pointed tools for turning and facing, the point
disappears very quickly giving a rough finish to the work. A tool with a small radius has
a longer l i f e and produces a better finish.
4)Chatter. This is a phenomenon which occurs in machines and is a function of their natural
resonance. There will be no doubt when it occurs. There will be significant vibration
accompanied by noise and the surface of the work will be very rough almost to the extent
o f having 'flats' on it. Once chatter has started on a workpiece it i s extremely difficult to
overcome.
The normal cause of chatter and points to check are:1) Too much overhang on the work or tool (or both).
2)Too high a speed.
3)Too much of the tool edge in contact with the work.
4) Work not clamped securely.
Chatter is much more easily overcome by checking the possible existence of these causes
BEFORE starting machining.
Other Machiningsperations.
Drilling,
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1/4" Drill Chuck and Key
Drilling (along the axis of the lathe) can be carried out in three ways using a drill chuck
mounted on a suitable arbor (see accessory list).
T h e normal method is to fit the drill chuck in the tailstock whilst the work is held in a chuck
etc. and rotated; the tailstock feedscrew or lever being used to feed in the drill. Alternatively
t h e drill chuck can be held in the headstock and rotated whilst the work is clamped to the
cross slide, the lead screw being used BY HAND to feed the work. This technique can also be
used with a tailstock drilling pad where the work is held against a pad (plain or vee) fitted
in the tailstock; the feed being imparted by the tailstock feedscrew or lever.
When drilling always start the hole with a centre drill and, during drilling, withdraw the drill
partially from time to time to clear the swarf. Large diameter holes may need 'piloting' that
is, drilling a small hole first and then following with the larger drill.
Thread Cutting,
D i e Holders
B u t t o n Dies.
B u t t o n Dies are used extensively t o c u t external threads. They are used o n the Lathe in a
h o l d e r which consists o f a b o d y which is bored through t o a sliding fit o n the tailstock
barrel; the end o f the body being recessed t o take standard b u t t o n dies. The holders are
available in the sizes (Cat. No. 10-226, 10-227, 10-228) t o accept dies o f 13/16", 1" and
I5/16" dia:
T o use:1) F i t the die i n the dieholder recess, securing it w i t h t h e 3 screws f i t t e d t o the holder. Note
t h a t the centre screw engages the split in t h e die and is used to set t h e thread diameter by
varying t h e gap.
2) Extend the tailstock barrel 20-25mm and slide the dieholder onto the barrel.
3) Feed t h e dieholder to t h e work, rotating the spindle BY H A N D t o cut the thread. Use a
c u t t i n g lubricant. When threading i n this way it is essential t o break o f f t h e swarf chips by
r o t a t i n g a fraction o f a turn back for each full t u r n forward.
A f t e r completing t h e cutting remove the die b y rotating the spindle BY H A N D in t h e reverse
direction. D O N O T drive t h e die o f f under power.
GPP~~:
Holes can b e threaded b y using t h e appropriate tap held in a drill chuck fitted to the tailstock.
A s w i t h dies, the complete operation is carried o u t by hand, again rotating back a fraction f o r
each turn t o break o f f the swarf chips.
N o t e t h a t when tapping, the tailstock is l e f t free to slide along t h e lathe bed. Feeding is by
h a n d pressure o n l y behind the taibtock.
Screwcutting ( 9 0 Lathe only).
Both external and internal threads can b e c u t using a single p o i n t t o o l as briefly described
in the section o n A u t o Traverse and Clutch. However, although this is a simple process in
principle it should be regarded as a more advanced turning skill and is therefore considered
to be outside the scope o f these notes.
T h e user's attention is n o w directed t o the 'Cowells 90 Lathe Handbook' which deals in depth
with this subject and the further application o f specialised accessories and techniques.
SECTION 4.
TURNING EXERCISE
F o r the purpose of the exercise assume that a piece of 19mm (34") Dia. mild steel bar, 25mm
( 1") long, must have its diameter reduced to % '"at one end for a length of 10 mm., the
turned diameter.
Procedure.
1. Fit the 4 jaw chuck to the lathe - set the bar in the chuck with W" projecting outside the
jaws - adjust the jaws so that the work runs true, using the technique outlined in the description
o f the 4 jaw chuck.
2. Fit a side turning tool similar to (No.7. from set No. 10-230A or No.4. from set No. 10-230)
in the tool holder slot nearest the chuck so that the cutting edge is exactly at the lathe centre
height and a t 90° to the lathe axis using shims if necessary to obtain the correct height setting.
Clamp the tool securely.
3. Select the lowest of the ungeared speeds (280 r.p.m.), that is, the drive belt must be on the
largest diameter pulley vee on the headstock spindle. DO NOT SWITCH ON.
4. Using the leadscrew and cross slide hand wheels, set the tool position so that it just touches
t h e end of the work. Note the reading on the leadscrew dial. Using the cross slide hand wheel,
move the tool back to clear the bar diameter and then towards the chuck, turning the leadscrew
10 FULL TURNS from the reading noted. Move the tool in until it just touches the bar and
turn the spindle BY HAND one revolution. You will now have a line scribed around the bar
exactly 10mm from the end; this can be used as a guide to the finished length when turning.
5. Move the tdol dear of the work back towards the end of the bar. Switch on. (Note that
t h e direction of rotation is anticlockwise looking a t the chuck jaws).
6. Move the tool in to just touch the bar and then move it to just clear the end. Note that
from this point on the tool will only be moved INTO the work using the cross slide hand
wheel, thus accounting for backlash, and that the cutting movement is obtained by use of
t h e leadscrew handwheel.
7. Set the tool 0.25 mm (%turn) in and take one cut along the bar, stopping just short of the
scribed line. Feed the tool slowly and evenly, using BOTH hands, when cutting. Move the
tool back to the end of the bar and then take a second cut of 0.25 mm. Switch the machine
OFF, and move the tool back to the end of the bar.
Note that switching off before moving the tool stops any tendency to cut on the return movement.
This practice should be followed at any measurement stage and when finishing.
8. Using a micrometer, measure the diameter of the turned length. Assuming that the diameter
is 36" (.7508') and that you are using a 0-1" micrometer, the reading obtained should be .75OV
minus the material removed. 2 cuts of 0.25 mm (.020" total) will have reduced the diameter
b y 0.040", therefore the reading shou Id be ,710" approx.
Let us say the reading is .710". Then, the amount of material s t i l l to be removed is .710" .500" (the required diameter) = .219" but remember that the tool only has to be moved in
by HALF the amount, therefore a further .105" has to be set on the cross slide handwheel to
bring the bar to the finished size. This can be done by using say 4 cuts of .020" (.5 mm) =
.080M, followed by a check measurement, then a cut of .008" (.2mm) followed by a check
measurement. At this stage you will be close to the required diameter and a further reduced
depth of cut can be made to leave a final cut of approximately ,003".
This finishing cut should be made as slowly and evenly as possible. Move the tool BACK from
the work at the end of this cut and switch the machine off.
Note that each cut should be 10 mm long, that is, to the leadscrew dial reading obtained when
scribing the mark in 4 above.
9. The turning exercise is now complete and the turned portion will be %" diameter, 10 mm
long and concentric with the 36" diameter.
I f you wished, you could now carry on and practise drilling and tapping on the same workpiece.
I f this is done without disturbing the bar in the chuck, the hole will also be concentric with
the diameters.
The principles used throughout the exercise are the basis of all machining operations and can
be applied to any work.
-..
Wheel and pinion cutter
Mounting; and maintainance
I , SECURING OF MOTORISED COUNTERSHAFT TO LATHE BASE:
TWO M6 TAPPED HOLES ARE PROVIDED IN THE REAR SURFACI: TABI.1,
AREA OF THE LATHE BASE.THE TWO FIXING BOLTS ARE SUPP1,IED.
REMOVE THE KNURLED ADJUSTER, SPRING AND SEATING WASHERS
FROM THE WHEEL AND PINION MOTOR MOUNTING PLATES.
COUNTERBORED SLOTS WILL BE SEEN IN THE BOTT'OM PLATE.
THE UNIT MAY THEN BE BOLTED TO THE REAR SURFACE TABLE ARI:I-\
IN THE DESIRED POSITION.
2, MOUNTING OF THE VERTICAL MILLING SLIDE:
THE SLIDE SHOULD BE SECURED INTO THE TWO REAR MOST TEE S1,OTS
OF THE LATHE CROSSLIDE WITH ITS TABLE FACING THE LATHE
I-IEADSTOCK,ENSURE CLEARANCE FOR ITS TABLE TO MOVE
VERTICALLY.
TO ENSURE THAT THE 'TABLE IS
TO THE LATHE HEADSTO(:I< 1.1.
IS ADVISED THAT THIS BE
SQUARE USING A DIAL 'rn-r'
INDICATOR.
3, MOUNTING OF THE MILLING SPINDLE HEAD:
THE MILLING SPINDLE HEAD MAY BE MOUNTED IN A VARIETY O F
POSITIONS IJPON THE VERTICAL MILLING SLIDE DEPENDING ON TI-113
WORK UNDERTAKEN.
ATTACH THE SPINDLE HEAD TO THE SLIDE BEFORE HOOKING UP TI-11.1
TOOTHED BELT DR1VE.A LOCATING TENON IS PROVIDED ON I'HE
MILLING HEAD BODY AND TWO M5 CAI' 1HEAD SREWS AND 'T13E NU'I'S
TO SECURE IT IN PLACE.
IT WILL BE NOTED THAT THE CARTRIDGE HOLDING THE MILLING
SPINDLE MAY BE REMOVED.THIS IS TO ALLOW THE MILLING HEAD
BODY TO BE INVERTED AND THERBY GAIN EXTRA HElGHT ABOVE THE
WORKPIECE.ONE M5 CAP HEAD SCREW LOCKS THE CARTRIDGE IN
PI-ACE.
A LUBRICATION HOLE WILL BE SEEN IN THE CARTRIDGE BODY.I'KOI?l
'TIME TO TIME THE CARTRIDGE SHOULD BE REMOVED OR SLID BACK SO
AS TO ALLOW A FEW PUMPS OF OIL.IT IS NOT POSSIBLE TO OVER 011
TI-IISCARTRIDGE,SO PUMP TI-IE OIL,CAN ~m- TI, OIL SEEPS FROI\/I 'rFII:
LUBRICATION HOLE..
4,TENSIONING AND POSITIONING OF TI-IE TOOTH BELT IIRIVE:
THE TOOTHED DRIVE BELT BETWEEN MILLING HEAD AND MOTORISED
LAYSHAFT SHOULD BE TENSIONED VIA THE KNURLED SPRING
ADJUSTER.DO NOT BE TEMPTED TO OVERTIGHTEN THIS ADJUSTER AS
UNDUE TENSION WILL BE EXERTED ON THE LATHE SLIDEWAYS
MAKING THEM STIFF TO 0PERATE.IT IS ONLY NECESSARY TO TIGH1"EN
UNTIL ANY TENDENCY TO BOUNCE IS ELIMINATED.CORREC1'
TENSIONING WILL SOON BECOME APPARENT WITH USE.
THE TOOTHED BELT DRIVE SHOULD RUN IN A VERTICAL POSITION
AUT0MATICALLY;BUT IT MAY BE NECESSARY TO MOVE THE BOTl'OM
I'ULLEY (WITH MOTOR STATIONARY) INTO THE CORRECT POSITTOU.
S~UARE
L
~
~
~
~
~
5, TENSIONING OF THE VEE BELT DRIVE
THE VEE BELT DRIVE BETWEEN 3 S'I'EP MOTOR PlJLLEY IIND LA)'S]j/\!:'l.
PULLEY MAY AFTER SOME TIME REQUIRE ADJUSTMEN'I'.
IT WILL BE NOTED THAT THE MOTOR HAS A MOUNTING CRADLE W1'1'114
X M5 HEX. BOLTS.THE CRADLE ITSELF HAS TWO RUBBER MOUN'I'S
BENEATH IT.IT IS POSSIBLE TO FINE TUNE THE ADJUSTMENT OF THE
BELT BY TIGHTENING OR LOOSENING THE HEX. BOLTS.
SHOULD THIS PROVE INSUFFICIENT,IT WILL BE NECESSARY T O MOVE
THE MOTOR BACK.
6, SLOW SPEED MOTOR PULLEY
PIJLLEYS ARE SECURED TO THE END OF THE MILLING SPINIlLl3 \'IA
TWO GRUB SCREWS A?' 120 DEGREES APART.THE MILLING SPIND1,E IS
HARDENED THROUGHOUT SO NO DAMAGE TO THE SPINDLE CAN
OCCUR.
7, MILLING SPINDLE BEARING ADJUSTMENT
IF END FLOAT CAN BE DETECTED BETWEEN THE MILLING SPINDLE c\VD
ITS BEARINGSJT WILL BE NECESSARY TO ADJUST THE SPLIT NU?'
ADJUSTER.DO NOT OVERTIGHTEN THE SPLIT NUT ADJUSTER; THE
SPINDLE SHOULD REVOLVE FREELY WITHOUT END PLAY.UNtIOOK 'fl-IE
TOOTHED DRIVE BELT TO VERIFY THIS.
8, FITTING THE DIVISION PLATE,DETENT AND ADAP'rOII TO THE
90ME LATHE.
TO FIT THE ABOVE ON THE 90ME LATHE IT WILL BE NECESSARY TO
REMOVE THE LATHE'S GEAR TRAIN.
1. REMOVE THE COLLAR HOLDING ON THE LARGE 64 TOOTH (;EAR 111THE BOTTOM O F THE ?'RAIN.
2,SLACKEN THE M5 CAP HEAD SCREW OF THE GEAR CARRIER PI-AT!:
WITHDRAW THE 64 TOOTH GEAR ALONG WITH THE COMPLETE C;E.AI<
TRAIN.NOTE THAT IT IS NOT NECESSARY TO DISTURB THE SETI'INGS 0 1 '
THE TWO DOUBLE GEARS ON THE TRAIN.
3, REMOVE THE KNURLED LOCKNUT FROM ?'ME LATHE HEADSI'OCK
SPINDLE,20 TOOTH GEAR (BE CAREFUL NOT T O LOOSE THE TINY KEY
BENEATH THE 20 TOOTH GEAR), AND TI-IE IZOUND BEARING ADJIJ3 FER
NUT.DO NOT REMOVE THE 64TOOTH SPINDLE GEAR,IT IS NOT
_NECESSARYTO DISTURB ITS SETTING.
4, THE DIVISIONPLATE ADAPTOR WILL NOW SCREW N T O PLACE.I1'
CAN THEN BE LOCKED IN PLACE VIA THE GRUB SCREW,BENEA'I'H
WHICH IS A BRASS PAD SO AS NOT T O DAMAGE THE SPINDLE TI--IREf\I).
5, THE DETENT MECHANISM MOUNTS IN THE SAME MANNER AS THl.
GEAR TRAIN PLATE.
9, LUBRICATION
THE LAYSHAFT SPINDLE RUNS IN OILITE BUSHES IMPKEGNAI'E~~l>
M I 1-14
OIL. HOWEVER, IT IS ADVISABLE 'rO LET A l,ITTL.E 011. INTO .THI:SI,
BIJSHES FROM TIME T O TIME.NO OILERS ARE PROVIDED,BUI' THE OIL.
WILL INGRESS IF THE ENDS OF THE LAYSI-IAFT ARE LUBRICA'TED.
ALWAYS KEEP THE LUBRICATION HOLE ON THE MILLING S P N D L E
CARTRIDGE IN THE UPRIGHT POSII'ION SO AS TO PREVENT D I ~ A I N A G
E.
10, FITTING THE DIVISION PLATE AND DETENT PLUNGER TO THE
90CW LATHE.
IT WILL BE NOTED THAT TWO M5 THREADED DIAGONALLY OPPOSED
HOLES ARE SITUATED IN THE HEADSTOCK END OF THE LATHE'S BED.
THESE HOLES MARRY TO THE DETENT PLUNGER MOUNTING PLATE.
SECURE THE PLATE IN POSITION WITH THE TWO M5 COUNTERSINK
SCREWS PROVIDED.
TO FIT THE DIVISION PLATE AND ITS ADAPTOR TO THE LATHE
HEADSTOCK SPINDLE.
REMOVE THE ALLJMINIUM END CAP FROM THE END OF THE LATHE'S
HEADSTOCK SPINDLE.
IT IS THEN NECESSARY TO REMOVE THE SPLIT SPINDLE ADJUSTER NUT.
THIS CAN BE ACHIEVED BY CAREFULLY SPLAYTNG THE NUT WITH A
SMALL DRIFT.(A SMALL SCREWDRIVER WILL SUFFICE IF A DRIFT IS NOT
TO HAND).
THE DIVISION PLATE AND ITS ADPAPTOR MAY THEN BE SCREWED ON
TO THE FINE THREAD IN PLACE OF THE SPLIT ADJUSTER.
SCREW ON THE PLATE AND ATTACHED ADAPTOR UNTIL IT GENTLY
BUTTS AGAINST THE BACKFACE OF THE BEARING CONE.
TWO M6 SCREWS WILL BE NOTED IN THE ADAPTOR AT 120 DEGREES
APART. BENEATH THESE SCREWS ARE BRASS PADS;THIS IS TO ENSURE
THAT NO DAMAGE CAN OCCUR TO THE FWE THREADS OF T m LATHE
SPINDLE.
THE CORRECT TENSION IS ACHlEVED WHEN THE LATHE SPINDLE
ROTATES FREELY WITH NO END PLAY IN THE LATHE SPINDLE.
SECURE BOTH M6 GRUB SCREWS.
NEVER USE THE LATHE UNDER POWER WITH THE DIVISION PLATE
AND ADAPTOR ATTACHED.
NOTES:
DETENT MECHANISM FOR THE 90ME LATHE:THE SPACER(16mm dia. Tapped M6 and M5) BETWEEN THE SLOTTED
PLATE (substitutes for the gear train plate) AND THE DETENT ARM (carries
the detent plunger) HAS BEEN DELIBERATELY MADE OVER LENGTH.
THIS IS BECAUSE THERE MAY BE A VARIATION IN HEADSTOCK
CONFIGURATION FROM MACHINE TO MACHINE.
THE IDEAL LENGTH FOR THE SPACER WILL BECOME APPARENT
ONCE THE DIVISION PLATE AND DETENT MECHANISM HAVE BEEN
MOUNTED ON YOUR LATHE.
THE SPACER CAN BE REDUCED TO THE REQUIRED LENGTH ON
YOUR LATHE- IT IS RECOMMENDED THAT AN EQUAL AMOUNT BE
MACHINED FROM EACH END OF THE SPACER.
COWELLS WILL BE HAPPY TO CARRY OUT THIS WORK (without
charge) SHOULD YOU NOT WISH TO DO THIS ON YOUR LATHE.
IN THIS CASE,PLEASE ADVISE US OF THE EXACT OVERALL LENGTH
REQUIRED.
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