This home-made 3-1/2in. lathe has novel features GEORGE B. ROUND,

This home-made 3-1/2in. lathe has novel features GEORGE B. ROUND,
--
This home-made 3-1/2in. lathe has
first of four articles by GEORGE B. ROUND,
novel features
in which he gives an account of the construction of a basic piece of machinery
machine to be described
is not put forward as an
“ ideal ” lathe, but as an
example of a plain lathe of simple
and straightforward construction to
which additions can be made as
time, fancy, or necessity dictates.
The lathe came into being through
the acquisition of a set of Stuart
No 10 engine castings and the
realisation that I had no means of
machining.
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Certain” limited facilities became
available, and it was decided to make
up a simple lathe rather than deal
with the engine castings, as this would
leave me with a lathe after the engine
was finished. As things turned out,
this was a wise decision, the facilities
for machining ending much sooner
than was expected.
Only a plain lathe was needed and
something on the lines of Maudslay’s
triangular bar bed was favoured, a
type I had always wanted to try out.
I dislike anything that looks obviously
home-made, however good its performance may be. As castings were
out of the question for a variety of
reasons, commercially obtainable sections, plus the junk heap had. to
provide the materials for construction.
They required careful selection to
ensure that appearance did not suffer.
It was decided to keep costs down to
the minimum, and in fact, the only
items purchased specially for the
machine itself, were Allen-type screws
and the mandrel ball-thrust bearing.
Design of the bed
The first item to be considered was
the bed, and the proposed design
was quickly modified for triangular
section bar is not readily obtainable,
nor particularly easy to machine
from round bar. The use of two round
bars was then considered but rejected
in favour of a square bar bed as
approximating more to the original
idea. No square bar over 1 in. being
to hand. the idea of arc-welding two
mild steel angles to form a square
tube was quite sound, and 2 in. x
2 in. x 3/8 in. thick angle was made the
basis of the design.
The lathe itself is 3-1/2 in. centre
height, taking about 13 in. between
22 OCTOBER 1959
centres, with a bed 27-1/2 in. long, the
extreme overall length being 2 ft 11 in.
and the overall width 15) in. It is
fitted with a form of back gearing
together with a worm drive to mandrel,
is screwcutting and has a back-shaft
drive for power traverse. Fig. 1 shows
the general arrangement and end
view, and collectively these show the
main features of the machine, which
started as a plain lathe and has
gradually acquired considerable elaboration.
To return to the bed, trouble was
encountered straight away. The
maximum traverse of the milling
machine was only about 20 in., and
this was not nearly long enough. A
large diameter plate was fixed to the
milling spindle with a single inserted
fly cutter, and with this a length of
27-1/2 in. could be machined. This had
to suffice although I would have
preferred a few more inches of bed.
No attempt was made to machine
the sides of the bed to a definite
dimension, care only being taken to
clean off all rough scale and to get
true parallel surfaces.
The four
corners were machined to clean up
the welds and to remove sharp
edges. Beyond drilling and tapping
eight holes, this finished the bed,
the fly cutter leaving the faces very
smooth and requiring little hand work.
The actual finished section of the bed
is shown in Fig. 2.
The headstock was the next consideration. It was fabricated by arc
welding mainly from angle and plate,
and is shown in Fig. 3. It was formed
from two 3/8in. thick plates cut to a
V at the bottom to fit over a 6-1/2in.
length of 2-1/2 in. angle with two smaller
angles between to act as stiffeners.
The bosses were formed of slices
of 2 in. dia. b.d.m.s. bar, the whole
being welded up into a strong and
rigid unit. Holes 3/8in. dia. were
drilled through the centres of the
bosses and at appropriate places in
the plates and bolted together for
location in weldine. Thicker plate
would have been used but it was not
available and 3/8 in. has proved to be
amply rigid in use.
General view of the 3-1/2 in. lathe to be described in these articles
293
MODEL ENGINEER
The milling machine was fitted with
a universal vertical milling attachment.
This was really accurate so that the
headstock was completely machined
in only two settings, first, set upside
down to machine out the underside,
using the vertical attachment set
alternately 45 deg. each side of the
centre.
Without disturbing the
setting, a vertical and horizontal
datum surface was machined on each
side of the V, as shown in section x-x,
Fig. 3.
This was used for locating squarely
on the table in the second set-up,
using the milling machine as a boring
machine, to bore and face the housings
for the bushes parallel with the V-base,
as with this form of bed any angular
adjustment of the headstock for
lining up is virtually non-existent.
The accuracy achieved with these
set-ups fully justified the trouble
taken.
It will be seen from Fig. 4 that the
mandrel front bearing is of substantial dimensions, 1-1/4 in. dia. x
2-1/4 in. long, the back bearing being
1 in. dia. x 1-5/16 in. long; the latter
would have been made longer had
material been available. If it becomes
necessary to fit a replacement, it will
be made 1-3/4 in. long, the mandrel
being turned down to suit.
Bearing bushes
The gunmetal bearing bushes are
solid and without a means of adjustment. This may cause some lifting
of eyebrows, but in my experience
with lathes of various makes and
sizes, only two were entirely free
from chatter and they were the only
two fitted with solid bushes. Admittedly, both had taper front bearings
for endwise adjustment, but a Pratt
and Whitney 4 in. had a parallel
rear bearing, and the other, a 5 in.
Pittler, was, I think, tapered though
I never removed the mandrel and so
cannot be certain.
However, the parallel bushes fitted
in my lathe show no signs of play
after nearly seven years of use. The
rear bush was fitted with the flange
between the housings to form a
shoulder for the thrust bearing to bed
against. The front bush was flanged
only for appearance.
Bright mild steel bar was used for
the mandrel and it was intended to
make the nose suitable for Myford
backplates and to take No 2 Morse
taper drills and centres, hence the
Headstock in closeup. Angle and plate
were the main items
used in fabrication
F A S T HEAD STOCK
MODEL ENGINEER
294
22
OCTOBER 1959
17/32 in. dia. hole through the body
of the mandrel. This was hurriedly
altered to 1 in. Whit. to use commercial hex. nuts welded to steel
discs as chuck backplates, which also
meant a change to No 1 Morse for
the taper. But 1 in. nuts are easily
obtained whereas specially threaded
backplates are not, except at a price.
A 1 in. roller thrust bearing of cheap
manufacture was used to take care
of thrust from drilling, etc., and a
plastic washer for the opposite thrust.
I was presented with some difficulty
in getting material for the bed section
of the tailstock. Eventually a cast
iron firebar was located which machined up into a nice rectangular bar
1-1/4 in. x 1-15/16 in . x some 27 in. long.
A piece 5 in. long was milled out to
fit the bed and a tailstock body
welded up from mild steel tube and
flat section bar. The tube was reamed
out to 7/8 in. dia. to take a lever-
22 OCTOBER 1959
Lathe mounted on a metal
cabinet with a self-contained countershaft unit
operated barrel, 7/8 in. dia., this being to the barrel. This is crude but
easier to make up than the screw- effective, and about the only suitable
operated pattern. It was also more method m the circumstances.
handy for drilling, as the machine
* To be continued on November 5
would have to do duty as a driller.
The bottom face was machined to
The Festiniog Railway, Vol. II,
suit the headstock centre height
by J. I. C. Boyd. T h e Oakwood
when bolted to the cast iron block.
Press, price 30s.
Two 5/16 in. hex. head setscrews were
R BOYD'S second volume
used and fitted solely for lining up
carries the history of the
purposes. I rarely require the tailFestiniog Railway from 1889 to
stock to be set over for taper turning,
the present time. It thus covers
and the extra refinement of a crossthe period from the death of
guide was felt to be unnecessary in a
Charles Spooner, the dynamic
plain lathe. Clamping of the barrel is
force behind this little railway,
by a thumbscrew and brass pad on
the Colonel Stephens era, the
post-war slump of 1923-1928, the
partial closure of 1939 and the
closure of 1946, and finally the
re-opening during 1955.
The author has made a lifetime’s study of the Festiniog
Railway and its associated lines,
and this book covers its subject
most thoroughly. Appendices are
included giving full details of the
locomotives, passenger coaches and
goods wagons; the track, stations,
yards and shops, as well as a
chronology from the original Authorisation in 1832.
Excellently produced, and well
illustrated with 47 photographs,
28 drawings, maps and plans, this
new book will appeal to all who
are interested in the fascinating
narrow-gauge railways of this
country.-R.M.E.
M
295
MODEL ENGINEER
3-1/2 in, SCREWCUTTING LATHE
Continued from 22 October 1959, pages 293 to 295
Constructing a suitable
slide-rest, cross-slide
and tool block
A
this stage the whole affair
was somewhat unwieldy, so
two temporary bench legs
were made up out of 1-1/2 in. slices
of angle welded to bits of 1/4 in.
plate. These were bolted to the
ends of the bed providing a
support while the head and tailstocks were fitted. The headstock
was secured by four 3/8 in. Whit.
Allen screws and the tailstock by
a forked clamp tightened with a
2-1/2 in. dia. black moulded plastic
handwheel, as shown in Fig. 5.
Attention was next turned to the
question of a suitable slide-rest.
After giving much consideration to
T
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By G.B. ROUND
Cutting change gearwheel using vertical slide
and directing attachment
various schemes to get the longest
t raverses, it was realised that in the
bed itself lay the obvious answer to
the problem, for here was the basis
of a slide the fulllength of the machine.
A V-groove was, therefore, milled in
each of two 6 in. lengths of the firebar and bolted to a piece of thick plate
surfaced on both sides, with a cutaway to clear the tailstock.
The bolt holes in the front piece
were slotted for adjustment and an
angle fitted to take the screws for
adjusting purposes. Two strips were
machined and screwed to the top face
with 3/16 in. Allen screws and this
made an excellent saddle.
The
arrangement was as shown in Fig. 6
and also in the photograph.
It was at this stage that a most
unexpected snag developed, for the
firm which had given me machining
facilities closed down and I had
barely time to finish off the mandrel.
However, a cross-slide was made up
from a chunk of cast iron and operated
by a long 3/8 in. Whit. bolt threaded its
full length, giving about 3 in. of cross
traverse. A piece of 1/2 in. round bar
threaded 1/2 in. Whit. was pressed into
service to operate the saddle up and
down the bed, both being operated
by handwheels salvaged from the
junk heap. A tool block was fashioned
out of an offcut from the firebar, and
a tryout to ascertain what could be
anticipated, seemed advisable.
The drive
This meant that a drive had to be
arranged and for this I used an 1/8 h.p.
Brook Cub motor together with a
9 in. V-pulley and belt. The 9 in.
pulley bore just fitted the end of the
mandrel. With the l-1/2in. pulley
already on the motor, it was felt that
it would do to just turn it round
and perhaps handle a 1/8 in. drill, and
in no time it was connected up and
running.
The motor was very large for such
a small rating, and as the 1/8 in. drill
seemed to have little effect on the
motor, a 1/4 in. drill was tried. This
too, was well within its stride, so
MODEL
ENGINEER
SCREWCUTTING LATHE
continued
turning was gingerly attempted with
complete success. In this state the
lathe was used for a considerable
time, machining up the Stuart engine
castings with no difficulty, the motor
giving ample power to turn the 3 in.
dia. flywheel.
One speed was a handicap and
eventually a 5 in. dia. pulley was
acquired which gave a much faster
speed for small drills and turning.
But it was awkward to change as it
involved moving the motor as well
as changing the pulley. So two fourspeed pulleys were turned up from
mahogany with diameters of 3 in.,
4 in., 5 in., and 6 in., arranged in an
angle iron frame on two 1/2 in. shafts,
one above the other.
The drive from the motor was on to
the lower shaft and a single V-belt
drive from the upper shaft went to the
mandrel, the diameter of the four-
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speed pulleys being too large to be
fitted between the headstock bearings.
Lignum vitae blocks were used for
the countershaft bearings and 1/4 in.
round leather belt for the cone pulleys.
A 4-1/8 in. dia. V-pulley was secured in
the normal position on the mandrel
with a 5/16 in. Allen grubscrew, and an
A size V-belt drive from the countershaft completed the arrangement.
Square threaded screw
This extra load had little effect on
the motor, and it was much more
convenient in use. As the end of the
mandrel was now free, I had thoughts
of making some sort of automatic
traverse. At this stage a friend produced a square threaded screw #in.
dia. It was too short for a normal
leadscrew, too long for the available
traverse of the saddle, being screwed
for its entire length. Above all, it
had seven threads per inch, but it was
much better than the 1/2 m. screwed
bar I was using, and extended my
plans to include screwcutting.
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- DE T A I L
ENGINEER
All turning had to be done on the
lathe itselfand to fit this screw called
for careful planning. Once the existing
traverse screw was removed the lathe
was out of action as far as turning
was concerned. Because of this new
dwarf legs were first made, the one
at the headstock end being of box
form, and welded up from angle,
channel and flat bar, as shown in
Figs 7 and 8.
Next a nut was cast in white metal,
as there was no nut with the screw
and cutting a nut in the normal way
was out of the question. A mould
was made by cutting a recess in a
block of wood, with holes at each end
through which to pass the leadscrew,
the recess being twice the required
length of nut, and forming an open
topped mould. The white metal used
was a mixture of all the broken diecast toys I could find, melted in a
tin can on the gas stove and poured
into the open mould.
As soon as it was set, the mould was
split off and with little trouble, the
354
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5 NOVEMBER 1959
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cast nut was screwed off the leadscrew,
which had been “ smoked ” to prevent
sticking, and then cut into two, thus
providing a spare nut when required.
The resulting thread was good, and
the metal stands up well to wear, so
that it will be a long time before
the spare is needed.
*To be continued on November 19
WORKING DRAWINGS
FOR A MARINE BOILER
For the ship modelling enthusiast who is seeking a suitable
boiler to power the engine of his
tug the Scotch return-tube marine
boiler has a lot to recommend it.
Being of compact design it fits
snugly in the limited length of a
vessel such as Gondia, which has
a length of 42in., a beam of
10 in. and a draught of 5 in.
Working drawings for a Scotch
marine boiler are now available.
The details are contained on one
sheet, price 6s. 6d. including
postage, and may be had from
the Plans Service, Percival
Marshall Ltd., 19-20 Noel Street,
London Wl. Plans for Gondia
are also obtainable, price 14s. 6d.
OPEN LEG
5 NOVEMBER 1959
355
MODEL ENGINEER
3-1/2 in. SCREWCUTTING LATHE
Continued from 5 November 1959, pages 353 to 355
Fitting a new
,
cross-slide and
other units
By G. B. ROUND
T
leadscrew brackets were
made up from mild steel
angle. At the tailstock end
a steel sleeve made from scrap
with a brass bush was used. This
was secured with a fine thread
locknut, the sleeve being already
threaded to suit. For the headstock end bracket, brass bushes
forced into suitably sized holes
were used.
Two bushes were fitted to enable
a reduction gear to be added at a
future date, to give the equivalent of
an 8 t.p.i. leadscrew for changewheel
calculations. It also helped to offset
the shortness of the leadscrew and
provide room for a clutch instead of
the more usual split nut arrangement.
This is shown in Fig. 9 whichillustrates
the final form of leadscrew and clutch.
HE
Adapting the leadscrew
To adapt the leadscrew, it was
necessary to turn down a plain portion
at each end. This was done by fitting
.a brass bush in place of the tailstock
barrel and using the tailstock body
as a steady while the screw, held in
the four-jaw chuck, was being turned
down. Both ends were thus treated,
the small portion of screw held in the
chuck being cut off afterwards. A
plain extension piece was then fitted
and pegged at the tailstock end. It
was left on the long side to take a
handwheel and leave room for possible
future developments.
The nut was secured to the saddle
by means of a cage, bent up from
16-gauge sheet riveted to an angle
bracket and attached by a couple of
19
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NOVEMBER 1959
421
MODEL ENGINEER
Allen screws. It allows for the nut
being readily removed and at the
same time restrains it from turning
and moving endwise, see Fig. 10. An
apron or cover, Fig. 11, was also
fitted to keep swarf off the leadscrew
as far as possible. This was sprung
into place and secured endways by
means of a tab, held by two screws
at the right-hand end.
A chip tray, Fig. 12, was made and
fitted between the lathe and the bench
to help retain turnings and keep things
tidy.
Being restricted for bench space,
it was felt that a separate stand for the
lathe would be a valuable asset and as
a quantity of 20-gauge galvanised
sheet offcuts were to hand, a cabinet
stand was designed to suit the sizes
available.
The arrangement and
SHELF
422
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19 NOVEMBER 1959
details of this are shown in Fig. 13
and also in the photograph of the
complete machine.
With the exception of the 14-gauge
backplate and the angle feet, it was
constructed throughout from 20-gauge
sheet fastened together with 1/4 in.
19 NOVEMBER 1959
galvanised gutterbolts. It has proved
to be rigid and yet is much lighter
than cast or angle iron legs and
provides ample storage space for tools
and equipment belonging to the
machine.
The construction was simple, only
423
plain bends being used. Although I
had the use of a hand-folding machine,
all bends can be done between two
angles.
All pieces were formed,
drilled, and finally bolted together.
The countershaft angle pillars were
bolted to the cupboard sides through
MODEL
ENGINEER
the 14-gauge plate, thus making a
solid unit.
The object of the thicker plate for
the back of the cupboard was to
carry the motor and so form a selfcontained unit, but for a number of
reasons this has not been done. To
give a professional touch a monogram
plate was fitted over the cupboard
door. It was cut from plywood with
two of the plies cut away to leave
raised letters and surround. It was
in fact a pattern for a casting, used
as the casting.
The lathe was mounted with 1/4 in.
plywood packings between the feet
and chip tray, and also between tray
and cabinet top. It has proved very
satisfactory, 1/2 in. thick rubber pads
being inserted between stand and
floor as it is used in an indoor workshop
Changing power units
At this stage I acquired a Leyland
Barlow 6 in. power shaper with a
traversing head, complete with stand
and 1/2 h.p. motor. The first thing to be
done was to arrange a drive to the
lathe from the shaper motor and so
free the lathe motor to work a sensitive
drilling machine which had been made
up in the meantime from oddments.
Up to this time all drilling had been
done on the lathe.
With the advent of the shaper, a
new cross-slide was made up in steel,
as shown in Fig. 14. It has a number
of tapped holes instead of T-slots, and
the fitting of a topslide was now
I wanted to get ample
essential.
clearance between the tailstock and
topslide handle and also to try out a
square guide in place of the usual
V-pattern.
As I still had some of the firebar
left, a piece was machined as detailed
in Fig. 15. The slide pivots on a
3/8 in. Allen screw, which was also
used as the main fixing, with an angleplate attached to the side, and curved
slots with setscrews to facilitate
setting for taper turning. These are
clearly shown in the photograph.
* To be continued on December 3
Saddle and topsIide with four-tool
turret. Note offset topslide screw
MODEL ENGINEER
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424
19 NOVEMBER 1959
3-1/2 in. SCREWCUTTING LATHE
Continued from 19 November 1959, pages 422 to 424
Completing the vertical slide,
back gear and
change wheels
By GEORGE B. ROUND
T
topslide nut was formed in one piece with the keep
plate and brings the operating screw well clear of the
tailstock. There is no tendency to bind and the slide
operates smoothly and does not require to be adjusted as
tightly as is necessary with a V-slide. The success of this
topslide prompted the making up of the vertical slide shown
in Fig. 16. Construction was similar to the topslide, except
for a single 1/2 in. bolt which is used to ‘allow for angular
HE
setting when required.
Again a number of tapped holes are used instead of T-slots.
All feed screws are 3/8 in. dia. x 16 t.p.i. as I prefer to work in
sixteenths rather than tenths of an inch. I am considering the
advisability of changing to 20 t.p.i. so as to fit feed dials graduated
in thous. But I feel that this thread is too fine for feedscrews, and
a lot of work is involved in making 10 t.p.i. square-thread screws
for all Slides.
A small electric motor from a Burroughs calculating machine
had been obtained
to drive the drilling
machine before I
had the shaper. This
was fitted with
a gearbox which
yielded a bronze
worm wheel and
steel worm with a
ratio of approximately 10-1/2 : 1. It
also had a peculiar
clutch arrangement
fitting on a shaft of
the same diameter
as the leadscrew extension, which gave
promise of a fine
feed a la Pittler.
The worm was
made in one piece
with the shaft, but
was detachable from
the motor armature? and fitted into
a piece of 1 in. x
14-gauge steel tube,
secured to the end
leg of the bed by
an odd aluminium
casting.
An extension shaft allowed for the fitting of
a pulley at the rear
of the machine to
MODEL
ENGINEER
482
3 DECEMBER 1959
View of the handandpower drive to
leadscrew at tailstock end of bed
clearly shows this arrangement, together with the finalised form of power
drive to give a longitudinal feed.
The vertical slide in use with the
side and face milling cutters of 3 in.
and 4in. dia., emphasised the need
for a back gear. This was also a
necessity for screwcutting, which by
this time was deemed to be essential.
Screwcutting meant change wheels.
These in turn, meant some form of
indexing the blanks for cutting the
teeth, all of which I was determined
to produce on the lathe itself. These
additions were more or less fitted
concurrently as the various requirements were dependent on one another.
VERTICAL
SLIDE
.
enable a power drive to be arranged
later.
The worm wheel, together with
the centre portion of the clutch,
revolves loosely on the shaft, and
the outer portion, to which a handle
is fixed, was pinned to the shaft,
thus driving the leadscrew through
the medium of a removable pin. As
the worm has seven starts this gearing
is reversible. After a slow traverse
with the handwheel or power feed,
the saddle can be returned for another
cut by means of the handle without
3 DECEMBER 1959
the necessity for disengaging the
clutch. This is an advantage when
screwcutting as it is not essential for
the wormwheel to be disconnected
from the leadscrew.
This was a fault on my 5 in. Pittler,
where it was possible to get the wormdriven screwcutting gears engaged at
the same time as the worm-driven
feed at the opposite end of the leadscrew. No doubt Pittler fitted some
sort of device to prevent this occurring,
but if so, it had been removed from
my machine. The picture on this page
483
Sorting out the gears
In the search for a wormwheel
suitable for dividing, a broken circular
knitting machine was discovered. This
provided a worm and wheel, but of
77 teeth-too large for a dividing
head, but big enough to fit on the
mandrel of the lathe. Although this
was an awkward number for dividing
purposes, it was better than nothing.
Also discovered were two gearwheels
of 80 and 90 teeth and 1.5 module
pitch, of which size I had a milling
cutter: No 8 for 135 teeth and over.
These, together with some useful bits
and pieces from the knitting machine,
were all the ready-made parts available.
Laying out these items in various
ways. I suddenly realised that by
breaking away from tradition an
effective backgear was possible. An
article in MODEL ENGINEER by George
Gentry many years ago provided the
solution, viz, an independent drive
for the mandrel when slow speeds
were required. Other additions (or
complications) suggested themselves
at the same time, and Fig. 18 shows
the final scheme, also seen in the
MODEL ENGINEER
second picture given here.
The 80 T wheel would just fit on
the mandrel if a slight clearance was
cut in the stiffening angles of the headstock, allowing the 90 T wheel to be
used as an idler wheel between an
18 T wheel on the drive shaft, giving
a ratio in the region of 4-1/2 : 1.
At the same time the worm and
wheel together with their cast iron
frame, were fitted with their integral
bevel gear drive to give an extra low
gear when desired, i.e., for circular
milling.
Both were driven by a
3-3/4 in. dia. V-pulley, also off the
knitting machine.
All this was
carried by two plates secured to a
channel bracket bolted to the box
leg at the rear of the headstock.
Fixing the 80 T gear
Brass was used for the 18 T gear,
this being easier to cut in the circumstances. With a little touching up
with a fine file to remedy the deficiencies of the shape of the teeth as
left by the cutter, the basic elements
were complete. Fixing the 80 T gear
to the mandrel was something of a
problem, as owing to the solid bearing
bushes for the mandrel, raised keys
could not be fitted until the mandrel
was in place. Furthermore, the keyway had to be cut by ha d. So as the
pulley had previously b een secured
with an Allen grubscrew, it was
decided to use the same method with
the addition of a dimple in the mandrel
for greater security.
The wormwheel and 80 T gear were,
therefore, bored a close fit to the
mandrel and before final assembly,
the pulley and wormwheel were
drilled with clearance holes, and the
80T gear with tapped holes for four
2 BA hex. head bolts to secure all
three together as one unit.
These were assembled individually
on the mandrel and the four bolts
tightened up. At the same time a
new 1 in. ball-thrust was fitted. It
was felt the arrangement deserved a
Reduction gear drive to mandrel
MODEL ENGINEER
R E D U C T IO N
thrust race that was above suspicion,
and that it would avoid the necessity
for dismantling later to fit a new race.
Assembly went well, tightening up
being a bit tricky owing to the confined
space. Finally, the whole unit was
solid with the mandrel, and not until
the reduction gearing had been in use
for some time was it discovered that
the grubscrew in the pulley had not
been tightened. Friction alone had
provided an adequate drive due no
doubt to slight inaccuracy in facing
the bosses.
Changing gear
The gear unit has proved most
effective and rigid in use, backgear
being engaged by sliding the 90 T
idler wheel into mesh with mandrel
and drive shaft gears. Withdrawing
a spring-loaded pin in the countershaft V-pulley drives the mandrel
direct, two movements only being
necessary as in normal backgearing.
The bevel gears for the extra low
ratio gearing are only in mesh when
required, being secured by a grubscrew. The frame carrying the worm
is secured by a locknut in the engaged
or disengaged positions,, this frame
being pivoted on the drive shaft.
A detachable handle on the drive
shaft allows the mandrel to be turned
slowly by hand for special operations,
and a 3 in. dia. pulley screwed to the
upper four-speed countershaft pulley
484
GEAR
U N IT
provides an adequate range of speeds.
It is a reduction gear rather than a
backgear. The drive shaft is, of course,
always revolving whether the gear is
in use or not-unless the belt is
removed. But this is not a serious
drawback. Provision has also been
made for fitting a handle at the top
of the vertical worm shaft.
To cut the gears a dividing head on
the direct indexing principle was made.
A gear cutting set-up on one of the
change wheels is shown in the issue
for November 5. A block of duralumin
was used for the body. Two interchangeable spindles were used, one
with a 3/8 in. dia., and one (as drawn)
with a 5/8 in. dia. seating for the gear
blanks being cut.
Division plates, four in number so
far, are in 1/8 in. thick hard aluminium
sheet, brass not being available.
Steel was considered too hard and
troublesome in which to drill a large
number of small holes. The aluminium has proved to be quite satisfactory.
I made a drilling spindle to drill the
holes, the body being formed from a
piece of 1 in. dia. round brass bar,
with a No 0 size Jacobs chuck fitted
to a taper on the spindle. When in
use, the gadget is clamped on the
topslide and driven by a spring belt
from the 1/8 h.p. drilling machine motor,
set up in a convenient position.
* To be continued on December 17
3 DECEMBER 1959
3-1/2 in. SCREWCUTTING LATHE
Fitting the gears
and other parts
Continued from 3 December 1959, pages 482 ta 484
By GEORGE B. ROUND
M
gearwheels were
borrowed and fixed on
an extension of the lathe
mandrel to divide the plates during
drilling, the plates being held on
a stud in the centre hole to ensure
concentric rings of holes. These
were first “ spotted ” with a l/32 in.
centre drill a n d then opened out
to 5/64 in. dia. using the same
set-up.
ACHINE-CUT
The drawing shows the details of
the spring-loaded plunger.
dividing head has also been used on
the shaping machine, with equal
success for gearcutting as on the
lathe. The fly cutter is mounted in a
toolholder and fed downwards for each
tooth. This makes an interesting
variation in the method of cutting
the teeth involved in a set of change
wheels.
All change gears are 20 d.p., this
being settled by a Myford gear of
65 T that was already to hand. It
was used as a gauge in grinding the
flv cutter and it also meant one gear
less to cut. A small amount of easing
with a fine file was necessary for the
smaller gears to ensure smooth running. Various materials were used for
the gears, brass, steel, cast iron and
Tufnol, and the complete set consists
of 20, rising by fives to 80, plus 63
and 100 and duplicates of 20 and 30.
All are 3/8 in. wide x 5/8in. bore, the
100 wheel being made from two 3/16 in,
thick layers of Tufnol riveted together.
The cluster gear
Fig. 21 shows the arrangement of
the cluster gear, which is of the fivewheel type, a design I wanted to try
out as it is considered to be free from
the “ gathering into mesh ” effect of
the four-wheel pattern. The cluster
gears are of Tufnol and the mandrel
and stud wheels of steel. All are of
20 d.p. x 3/8 in. face and have proved
exceptionally smooth in action.
Change gears, feed
shaft drive, reduction and worm drive
MODEL
ENGINEER
544
Detailed in Fig. 22 is the pivot pin
for the cluster frame. The leadscrew
clutch is detailed in Figs. 9, 24 and 25.
It is of steel throughout and 1/8 in. dia.
stop pins are provided in the box leg
to limit the travel of the operating
lever.
Details of the quadrant and change
gear studs are given in Figs. 26, 27
and 28, these. again being in steel.
The quadrant has a separate arm and
curved slot for locking in position,
an Allen screw in the boss being used
for temporary adjustment when meshing the gears. The boss is a separate
item riveted to the quadrant.
An odd shaped bracket from the
knitting machine, together with a
pair of dural bevel gears from a
scrapped aero engine, finalised the
longitudinal power feed. These were
fitted as shown in Fig. 29 and Fig. 7.
An aluminium packing block suitably
cut to shape furnished the bracket
at the tailstock end of the bed. The
backshaft is 1/2 in. dia. x 16-gauge
drawn steel tube, with solid ends
pegged to the tube, and a cork washer
1 in. dia. recessed into one of the bevel
gears, making an effective clutch.
The pulleys
A hardwood pulley, Fig. 30, is
fitted in place of the change wheel on
the stud- and drives by means of a
spring belt to the pulley on the backshaft. This belt is crossed to clear
the driveshaft for the mandrel reduction gear. The backshaft pulley is
“ rubber ” and was a moulded castor
wheel with an inserted boss of steel,
turned down and grooved for the belt
and has exceptional gripping power.
The lever fed tailstock barrel was
at some disadvantage since drilling was
now normally taken care of by a
separate machine. It had insufficient
control over the drill for heavy drilling
in the lathe and so a new barrel,
operated bv a handwheel and screw.
as shown in Fig 31, was made and
fitted. It can, however, be withdrawn
by loosening two grubscrews and the
lever-operated barrel can then be
inserted in a couple of minutes
whenever required.
With the change in driving motors
came the problem of continually
stopping and starting. The 1/8 h.p.
motor was dealt with by a 5 amp.
17 DECEMBER 1959
F EE D PULLEY
026
_ .” _I - I^ - - -.
I
tumbler switch in a metal case mounted
on a length of steel conduit bolted to
the cabinet stand at the right-hand end,
[ME, October 22]. This proved to be
unsuitable for the 1/2 h.p. motor and
for a short time, recourse was had
to flicking the round belt on and off
the four-speed pulleys. This was a
most
unsatisfactory
arrangement
which frequently resulted in the belt
breaking at the fastener, usually
when one was in a hurry to complete
the job in hand.
Some form of clutch was obviously
called for, as owing to the use of
a new four-speed pulley was turned
up from mahogany, and fitted with
ball races so as to run freely on the
shaft, and having a lining piece of
1/8 in. plywood on the large face. To
this was glued a disc of sheet cork,
1/4 in. thick, to provide the friction drive.
A 6 in. dia. light alloy V-pulley
was fastened to a shouldered steel
sleeve and faced off true with the bore
of the sleeve, and suitably marked for
reassembling. The 1 in. roller thrust
race originally fitted to the mandrel
was placed between the pulley and
shoulder of the sleeve, with a light
in conjunction with pulleys grooved
to the same angle as for A-size Vbelts. These too, have proved to be
capable of transmitting all the power
required to drive the mandrel. While
the work the lathe has done does not,
of course, compare with factory
production speeds and feeds, it has
handled work up to its maximum
capacity in steel.
The machine incorporates a number
of controversial features, some intentionally and some due to the fact
that this was the only available means
of construction. The parallel non-
rubber pads under the cabinet
shaping machine stands, a flat
with fast and loose pulleys
unsuitable since neither machine
fastened to the floor.
aluminium casing to carry two withdrawal pins, the sleeve being keyed to
the shaft, but free to slide endways.
Another collar and a spare valve
spring completed the set-up.
A clutch lever made up from 5/8 in.
x 1/8 in. flat bar, with a leverage of
4 : 1 was pivoted below the 1 in.
thrust race. It was controlled by a
handle having a boss with a pin
arranged to give an over-centre
movement to a connecting link with
the top of the clutch lever, the amount
of axial movement at the clutch being
about l/32 in. It has not been found
necessary to modify the original
arrangement and there is complete
absence of slip under any load.
Round belts 1/4 in. dia. are used for
both main and reduced speed drives,
adjustable bearings are perhaps the
most outstanding matters of controversy, but the fact remains that
they have proved eminently satisfactory with complete freedom from
chatter. The square edge slides also,
have been so successful that I prefer
them, wherever possible, to V-slides.
They are much easier to make up and
still give that smooth silky action so
desirable.
In use, the bed has proved to be
very rigid, the square tubular section
being, of course, highly resistant to
torsional strains, and possibly the
strongest form for this purpose. My
only real regret is that it is not several
inches longer, but that was not
possible under the circumstances.
* Concluded next week
and
belt
was
was
Trouble free
As an experiment, the arrangement
shown in Fig. 32, and in section in
Fig. 33 was made up. After more
than two years in use, it has proved
completely effective and trouble free,
while at the same time being smooth
in operation and yet simple to make
up. The 1/2in. dia. lower shaft of the
countershaft unit was replaced by one
of 5/8 in. dia. running in die-cast alloy
bearings, located at each end by
collars, and having a ball-thrust
washer at the right-hand end. Next,
MODEL ENGINEER
546
17 DECEMBER 1959
3-1/2 in. SCREWCUTTING LATHE
Concluded from 17 December 1959. pages 544 to 546
Machining the
guide ring and
base block
By GEORGE B. ROUND
Oval-fuming chuck in operation
T
general arrangement of
the chuck together with details of the moving parts,
are shown in Fig. 34, and Fig.
35 shows details of the fixed items.
The maximum amount of eccentricity that can be given to the guide
ring is 1/2 in., giving a difference of
1 in. between the major and minor
axes of the ovals. This allows quite
a wide range of work to be done. It
was constructed mainly of steel, the
backplate being cut from a 5 in. dia.
circle of 3/8 in. thick plate to which a
boss had been welded. After the
guides and cover plates had been
secured in position, the whole was
turned up to give a clean finish, hence
the odd dimension of 4-15/16 in. for the
overall diameter.
Bright mild steel bar 2 in. x 3/8 in.
was used for the slide and a piece of
the same material, sawn lengthwise,
for the guide pieces. The cut was
made off-centre in order to allow for
the gib strip, and at the same time
keep the chuck symmetrical and in
balance. The cover strips were cut
from 2 in. x 3/16 in. bright mild steel
bar, and the gib strip from 3/16 in.
thick brass bar, the latter being
located endwis e by means of dimples
for the ends of the adjusting screws.
The screwed nose, of similar size
to the mandrel nose, was shrunk into
the slide, lightly riveted at the back,
faced off flush and drilled and reamed
with a 5/16 in. dia. hole for locating the
slide centrally on the backplate during
construction. This was done by means
of a plug with a spigot, registering in
the same recess that locates the backplate to the mandrel nose.
A strip of tissue paper under each
cover plate provided just enough
HE
MODEL
ENGINEER
PLAN
IN PART SECTION
578
24 DECEMBER 1 9 5 9
clearance for a nice sliding fit. Before
finally removing the centre plug, a
hole 1/8 in. dia. was drilled and reamed
in a convenient position so as to
locate the slide at any time in a central
position. Each guide was also fitted
with two dowels to the backplate to
ensure permanent alignment.
To the back of the slide are fixed
two shoe guides made of 3/4 in. x 3/16 in.
brass T, with 3/8 in. thick mild steel
packing blocks between them, to clear
the backplate. Each is secured by
four 3/16 in. roundhead screws in
lightly counterbored holes, and finally
located with dowel pegs to prevent
lateral movement in operation. The
shoe is of 1/2 in-thick Tufnol, the impregnated linen grade, two opposite
edges being made parallel and then
bored exactly central to a nice running
fit on the guide ring.
This guide ring was turned from
a 2-1/2 in. mild steel shafting collar,
the grubscrew hole forming an excellent oil pocket, although larger
than necessary. It is clamped in
position in the fixed backplate by a
2 BA Allen screw, at exactly the
height of the lathe centres.
The backplate rests at the bottom
upon a base block shaped to suit the
bed section, and is secured to a clamp
bar of 1/2in. square bright mild steel
bar. This in turn rests upon, and is
bolted to, a lower clamp bar of
similar section provided with slots
screwed to the base block, thus
providing for the adjustment of the
guide ring relative to the axis of the
mandrel in a horizontal plane.
The base block is, of necessity,
peculiar to the requirements of this
particular bed, and is made up from
mild steel angle and channel sections
welded together and clamped to the
bed in the manner of the tailstock.
This clamp also secures a similar
block carrying a small hand-rest
when required for hand turning.
In operation, the chuck is smooth
and easy running, taking good cuts
without chatter. It was made up for
plain oval turning only. For ornamental work an independent rotary
movement of the nose would be
necessary, but as this was not required,
the extra rigidity of the fixed nose was
considered a more desirable feature.
Other equipment, in addition to
that already mentioned, includes 3 in.
“ Scintilla ” and 2-1/2 in. “ Burnerd ”
three-jaw chucks, 49 in. “ Burnerd ”
four-jaw chuck, 6 in. dia. faceplate,
driver plate, tailstock drill pad, and
a sliding centre for taper turning.
Side and face milling cutters up to
4 in. dia., and a special 2 in. dia.
facing cutter,, are held on stub mandrels
in the four-jaw chuck, and a 6 in. x
1/16 in. cutter is used for deep cuttingoff or slitting.
The four-jaw chuck, I would add, is
still accurate and in first-class condition without shake in the jaws,
despite 20 years’ service. It is amazing
value for the 25s. it cost in 1939.
Cover plates are fitted to the cross-
Below: Body of oval-turning
chuck. It has been unscrewed
to show guide ring and shoe
24 DECEMBER 1959
579
MODEL ENGINEER
B ACK
PLATE
BASE
slide and the leadscrew gears to
exclude swarf, and there are also
removable shields at the back and
front of the chip tray, to confine
turnings, as far as possible, to the tray.
The machine and stand are finished
in an eau-de-nil green enamel paint,
making it easy to wipe down and
clean, besides looking effective. The
switch which formerly did duty as a
starter switch now carries an electric
light mounted on a flexible hoIder. A
40 w. bulb at 12 v. is used, operating
through a transformer, to prevent
risk of shock through shorting of
cables.
With regard to cost, the only items
purchased specially for this machine,
were the 1 in. ball-thrust race for 10s.,
and the various Allen screws and paint
about 35s. in all. My own scrap
box, and those belonging to friends,
provided the rest of the materials. q
GIANTS OF ENGINEERING
Continued from page 574
drying up of supplies first of the Baltic
pine from which they were made and
then of the yellow Quebec pine which
was substituted for it.
When it is realised that Brunel’s
shipbuilding achievements were largely
contemporaneous with his stupendous
railway works, some faint realisation
of his capacity for work and the
range of his intellect becomes possible.
Between 1836 and his untimely death
23 years later he designed three great
steamships,. each one in turn far
exceeding in tonnage anything ever
before attempted.
These were the Great Western,
built of wood and propelled by
paddles, the first real Atlantic liner,
the Great Britain, built of iron and
screw-propelled, and lastly the illstarred Great Eastern, also built of
iron but driven by screw and paddles.
MODEL
ENGINEER
The paddle engines, four-cylinder
double-diagonal oscillating (there are
magnificent models in the Science
Museum), had a stroke of 14 ft, the
longest of any engine of which 1 can
find a record.
The screw engines of the G r e a t
Britain were also of double-diagonal
type (not oscillating) working upwards
and driving the propeller shaft by
means of a chain geared up 3 to 1, i.e.
the propeller shaft ran at three times
the speed of the crankshaft. The
Great Western made no fewer than
67 Atlantic crossings in eight years.
All these ships, but particularly
the Great Eastern, were badly handicapped by inadequate dock and
harbour facilities. An outstanding
characteristic of the Great Eastern
was its marvellous manoeuvrability.
By the combined operation of paddles
and screw it could turn practically
about its own vertical centre line,
an invaluable feature in the days
580
when tugs were few and far between.
The difficulties of launching the
Great Eastern and the initial troubles
with its engines and boilers,, none of
which could be directly attributed to
Brunel, finally broke his health and
his heart and he died on 15 September
1859 when only 53 years of age.
Brunel was a man of immensely
forceful character and of strong
antipathies. He detested the pseudoscientist and equally the bone-headed
self-styled “ practical man.”
Perhaps the most fitting tribute to
him came from his friend and colleague
Daniel (afterwards Sir Daniel) Gooch
who wrote:
” On the 15 September, I lost my
oldest and best friend. By his death
the greatest of English engineers was
lost.”
Facts in this article have been taken
from Smiles’ Lives of the Engineers and
Zsambard Kingdom Brunel, by L. T. C.
Rolt (Longman and Co. Ltd.) 30s. q
24 DECEMBER 1959
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