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This home-made 3-1/2in. lathe hasfirst of four articles byin
which he gives an account of the con-struction of a basic piece of
machinery
GEORGE B. ROUND,novel features
I THE machine to be describedis not put forward as an ideal
lathe, but as anI
example of a plain lathe of simpleI and straightforward
construction to
which additions can be made astime, fancy, or necessity
dictates.The lathe came into being through
! the acquisition of a set of StuartNo 10 engine castings and
therealisation that I had no means ofmachining.
1 Certain limited facilities becameavailable, and it was decided
to make
i up a simple lathe rather than dealwith the engine castings, as
this wouldleave me with a lathe after the enginewas finished. As
things turned out,this was a wise decision, the facilitiesfor
machining ending much soonerthan was expected.
Only a plain lathe was needed andsomething on the lines of
Maudslaystriangular bar bed was favoured, atype I had always wanted
to try out.I dislike anything that looks obviouslyhome-made,
however good its per-formance may be. As castings wereout of the
question for a variety ofreasons, commercially obtainable
sec-tions, plus the junk heap had. toprovide the materials for
construction.They required careful selection toensure that
appearance did not suffer.It was decided to keep costs down tothe
minimum, and in fact, the onlyitems purchased specially for
themachine itself, were Allen-type screwsand the mandrel
ball-thrust bearing.
Design of the bedThe first item to be considered was
the bed, and the proposed designwas quickly modified for
triangularsection bar is not readily obtainable,nor particularly
easy to machinefrom round bar. The use of two roundbars was then
considered but rejectedin favour of a square bar bed
asapproximating more to the original
Iidea. No square bar over 1 in. being
Ito hand. the idea of arc-welding twomild steel angles to form a
squaretube was quite sound, and 2 in. x
i
2 in. x 3/8 in. thick angle was made thebasis of the design.
The lathe itself is 3-1/2 in. centreheight, taking about 13 in.
between
22 OCTOBER 1959
centres, with a bed 27-1/2 in. long, theextreme overall length
being 2 ft 11 in.and the overall width 15) in. It isfitted with a
form of back gearingtogether with a worm drive to mandrel,is
screwcutting and has a back-shaftdrive for power traverse. Fig. 1
showsthe general arrangement and endview, and collectively these
show themain features of the machine, whichstarted as a plain lathe
and hasgradually acquired considerable elab-oration.
To return to the bed, trouble wasencountered straight away.
Themaximum traverse of the millingmachine was only about 20 in.,
andthis was not nearly long enough. Alarge diameter plate was fixed
to themilling spindle with a single insertedfly cutter, and with
this a length of27-1/2 in. could be machined. This hadto suffice
although I would havepreferred a few more inches of bed.
No attempt was made to machinethe sides of the bed to a
definitedimension, care only being taken toclean off all rough
scale and to get
true parallel surfaces. The fourcorners were machined to clean
upthe welds and to remove sharpedges. Beyond drilling and
tappingeight holes, this finished the bed,the fly cutter leaving
the faces verysmooth and requiring little hand work.The actual
finished section of the bedis shown in Fig. 2.
The headstock was the next con-sideration. It was fabricated by
arcwelding mainly from angle and plate,and is shown in Fig. 3. It
was formedfrom two 3/8in. thick plates cut to aV at the bottom to
fit over a 6-1/2in.length of 2-1/2 in. angle with two smallerangles
between to act as stiffeners.
The bosses were formed of slicesof 2 in. dia. b.d.m.s. bar, the
wholebeing welded up into a strong andrigid unit. Holes 3/8in. dia.
weredrilled through the centres of thebosses and at appropriate
places inthe plates and bolted together forlocation in weldine.
Thicker platewould have been used but it was notavailable and 3/8
in. has proved to beamply rigid in use.
General view of the 3-1/2 in. lathe to be described in these
articles
293 MODEL ENGINEER
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The milling machine was fitted witha universal vertical milling
attachment.This was really accurate so that theheadstock was
completely machinedin only two settings, first, set upsidedown to
machine out the underside,using the vertical attachment
setalternately 45 deg. each side of thecentre. Without disturbing
thesetting, a vertical and horizontaldatum surface was machined on
eachside of the V, as shown in section x-x,Fig. 3.
This was used for locating squarelyon the table in the second
set-up,using the milling machine as a boringmachine, to bore and
face the housingsfor the bushes parallel with the V-base,as with
this form of bed any angularadjustment of the headstock forlining
up is virtually non-existent.The accuracy achieved with
theseset-ups fully justified the troubletaken.
It will be seen from Fig. 4 that themandrel front bearing is of
sub-stantial dimensions, 1-1/4 in. dia. x
MODEL ENGINEER
2-1/4 in. long, the back bearing being1 in. dia. x 1-5/16 in.
long; the latterwould have been made longer hadmaterial been
available. If it becomesnecessary to fit a replacement, it willbe
made 1-3/4 in. long, the mandrelbeing turned down to suit.
Bearing bushesThe gunmetal bearing bushes are
solid and without a means of adjust-ment. This may cause some
liftingof eyebrows, but in my experiencewith lathes of various
makes andsizes, only two were entirely freefrom chatter and they
were the onlytwo fitted with solid bushes. Ad-mittedly, both had
taper front bearingsfor endwise adjustment, but a Prattand Whitney
4 in. had a parallelrear bearing, and the other, a 5 in.Pittler,
was, I think, tapered thoughI never removed the mandrel and
socannot be certain.
However, the parallel bushes fittedin my lathe show no signs of
playafter nearly seven years of use. The
rear bush was fitted with the flangebetween the housings to form
ashoulder for the thrust bearing to bedagainst. The front bush was
flangedonly for appearance.
Bright mild steel bar was used forthe mandrel and it was
intended tomake the nose suitable for Myfordbackplates and to take
No 2 Morsetaper drills and centres, hence the
Headstock in close-up. Angle and platewere the main itemsused in
fabrication
294
F A S T HEAD STOCK
22 OCTOBER 1959
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17/32 in. dia. hole through the bodyof the mandrel. This was
hurriedlyaltered to 1 in. Whit. to use com-mercial hex. nuts welded
to steeldiscs as chuck backplates, which alsomeant a change to No 1
Morse forthe taper. But 1 in. nuts are easilyobtained whereas
specially threadedbackplates are not, except at a price.A 1 in.
roller thrust bearing of cheapmanufacture was used to take careof
thrust from drilling, etc., and aplastic washer for the opposite
thrust.
I was presented with some difficultyin getting material for the
bed sectionof the tailstock. Eventually a castiron firebar was
located which mach-ined up into a nice rectangular bar1-1/4 in. x
1-15/16 in . x some 27 in. long.A piece 5 in. long was milled out
tofit the bed and a tailstock bodywelded up from mild steel tube
andflat section bar. The tube was reamedout to 7/8 in. dia. to take
a lever-
Lathe mounted on a metalcabinet with a self-con-tained
countershaft unit
operated barrel, 7/8 in. dia., this beingeasier to make up than
the screw-operated pattern. It was also morehandy for drilling, as
the machinewould have to do duty as a driller.
The bottom face was machined tosuit the headstock centre
heightwhen bolted to the cast iron block.Two 5/16 in. hex. head
setscrews wereused and fitted solely for lining uppurposes. I
rarely require the tail-stock to be set over for taper turning,and
the extra refinement of a cross-guide was felt to be unnecessary in
aplain lathe. Clamping of the barrel isby a thumbscrew and brass
pad on
22 OCTOBER 1959 295
to the barrel. This is crude buteffective, and about the only
suitablemethod m the circumstances.
* To be continued on November 5
The Festiniog Railway, Vol. II,by J. I. C. Boyd. The
OakwoodPress, price 30s.
M carries the history of theFestiniog Railway from 1889 tothe
present time. It thus coversthe period from the death ofCharles
Spooner, the dynamicforce behind this little railway,the Colonel
Stephens era, thepost-war slump of 1923-1928, thepartial closure of
1939 and theclosure of 1946, and finally there-opening during
1955.
The author has made a life-times study of the FestiniogRailway
and its associated lines,and this book covers its subjectmost
thoroughly. Appendices areincluded giving full details of
thelocomotives, passenger coaches andgoods wagons; the track,
stations,yards and shops, as well as achronology from the original
Auth-orisation in 1832.
Excellently produced, and wellillustrated with 47 photographs,28
drawings, maps and plans, thisnew book will appeal to all whoare
interested in the fascinatingnarrow-gauge railways of
thiscountry.-R.M.E.
MODEL ENGINEER
R BOYD'S second volume
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3-1/2 in, SCREWCUTTING LATHEContinued from 22 October 1959,
pages 293 to 295
Constructing a suitable
slide-rest, cross-slide
and tool block By G.B. ROUND
AT this stage the whole affair Cutting change gear-was somewhat
unwieldy, sowheel using vertical slidetwo temporary bench legsand
directing attachmentwere made up out of 1-1/2 in. slicesof angle
welded to bits of 1/4 in.plate. These were bolted to the
various schemes to get the longesttraverses, it was realised
that in the
ends of the bed provid ing a bed itself lay the obvious answer
tosupport while the head and tail- the problem, for here was the
basisstocks were fitted. The headstockof a slide the fulllength of
the machine.was secured by four 3/8 in. Whit.A V-groove was,
therefore, milled inAllen screws and the tailstock byeach of two 6
in. lengths of the fire-
a forked clamp tightened with abar and bolted to a piece of
thick platesurfaced on both sides, with a cut-
2-1/2 in. dia. black moulded plastic away to clear the
tailstock.handwheel, as shown in Fig. 5.
Attention was next turned to theThe bolt holes in the front
piece
were slotted for adjustment and anquestion of a suitable
slide-rest. angle fitted to take the screws forAfter giving much
consideration to adjusting purposes. Two strips were
L___-_-
machined and screwed to the top facewith 3/16 in. Allen screws
and thismade an excellent saddle. Thearrangement was as shown in
Fig. 6and also in the photograph.
It was at this stage that a mostunexpected snag developed, for
thefirm which had given me machiningfacilities closed down and I
hadbarely time to finish off the mandrel.However, a cross-slide was
made upfrom a chunk of cast iron and operatedby a long 3/8 in.
Whit. bolt threaded itsfull length, giving about 3 in. of
crosstraverse. A piece of 1/2 in. round barthreaded 1/2 in. Whit.
was pressed intoservice to operate the saddle up anddown the bed,
both being operatedby handwheels salvaged from thejunk heap. A tool
block was fashionedout of an offcut from the firebar, anda tryout
to ascertain what could beanticipated, seemed advisable.
The driveThis meant that a drive had to be
arranged and for this I used an 1/8 h.p.Brook Cub motor together
with a9 in. V-pulley and belt. The 9 in.pulley bore just fitted the
end of themandrel. With the l-1/2in. pulleyalready on the motor, it
was felt thatit would do to just turn it roundand perhaps handle a
1/8 in. drill, andin no time it was connected up andrunning.
The motor was very large for sucha small rating, and as the 1/8
in. drillseemed to have little effect on themotor, a 1/4 in. drill
was tried. Thistoo, was well within its stride, so
MODEL ENGINEER
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SCREWCUTTING LATHEcontinued
turning was gingerly attempted withcomplete success. In this
state thelathe was used for a considerabletime, machining up the
Stuart enginecastings with no difficulty, the motorgiving ample
power to turn the 3 in.dia. flywheel.
One speed was a handicap andeventually a 5 in. dia. pulley
wasacquired which gave a much fasterspeed for small drills and
turning.But it was awkward to change as itinvolved moving the motor
as wellas changing the pulley. So two four-speed pulleys were
turned up frommahogany with diameters of 3 in.,4 in., 5 in., and 6
in., arranged in anangle iron frame on two 1/2 in. shafts,one above
the other.
The drive from the motor was on tothe lower shaft and a single
V-beltdrive from the upper shaft went to themandrel, the diameter
of the four-
speed pulleys being too large to befitted between the headstock
bearings.Lignum vitae blocks were used forthe countershaft bearings
and 1/4 in.round leather belt for the cone pulleys.A 4-1/8 in. dia.
V-pulley was secured inthe normal position on the mandrelwith a
5/16 in. Allen grubscrew, and anA size V-belt drive from the
counter-shaft completed the arrangement.
Square threaded screwThis extra load had little effect on
the motor, and it was much moreconvenient in use. As the end of
themandrel was now free, I had thoughtsof making some sort of
automatictraverse. At this stage a friend pro-duced a square
threaded screw #in.dia. It was too short for a normalleadscrew, too
long for the availabletraverse of the saddle, being screwedfor its
entire length. Above all, ithad seven threads per inch, but it
wasmuch better than the 1/2 m. screwedbar I was using, and extended
myplans to include screwcutting.
All turning had to be done on thelathe itselfand to fit this
screw calledfor careful planning. Once the existingtraverse screw
was removed the lathewas out of action as far as turningwas
concerned. Because of this newdwarf legs were first made, the oneat
the headstock end being of boxform, and welded up from
angle,channel and flat bar, as shown inFigs 7 and 8.
Next a nut was cast in white metal,as there was no nut with the
screwand cutting a nut in the normal waywas out of the question. A
mouldwas made by cutting a recess in ablock of wood, with holes at
each endthrough which to pass the leadscrew,the recess being twice
the requiredlength of nut, and forming an opentopped mould. The
white metal usedwas a mixture of all the broken die-cast toys I
could find, melted in atin can on the gas stove and pouredinto the
open mould.
As soon as it was set, the mould wassplit off and with little
trouble, the
j ./, :/ 1
ENGINEER 354 5 NOVEMBER 1959
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I 4 B O X L E G
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cast nut was screwed off the leadscrew,which had been smoked to
preventsticking, and then cut into two, thusproviding a spare nut
when required.The resulting thread was good, andthe metal stands up
well to wear, sothat it will be a long time beforethe spare is
needed.
*To be continued on November 19
OPEN LEG
355
WORKING DRAWINGSFOR A MARINE BOILER
For the ship modelling en-thusiast who is seeking a
suitableboiler to power the engine of histug the Scotch return-tube
marineboiler has a lot to recommend it.Being of compact design it
fitssnugly in the limited length of avessel such as Gondia, which
hasa length of 42in., a beam of10 in. and a draught of 5 in.
Working drawings for a Scotchmarine boiler are now available.The
details are contained on onesheet, price 6s. 6d. includingpostage,
and may be had fromthe Plans Service, PercivalMarshall Ltd., 19-20
Noel Street,London Wl. Plans for Gondiaare also obtainable, price
14s. 6d.
5 NOVEMBER 1959 MODEL ENGINEER
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,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
THE leadscrew brackets weremade up from mild steelangle. At the
tailstock enda steel sleeve made from scrapwith a brass bush was
used. Thiswas secured with a fine threadlocknut, the sleeve being
alreadythreaded to suit. For the head-stock end bracket, brass
bushesforced into suitably sized holeswere used.
Two bushes were fitted to enablea reduction gear to be added at
afuture date, to give the equivalent ofan 8 t.p.i. leadscrew for
changewheelcalculations. It also helped to offsetthe shortness of
the leadscrew andprovide room for a clutch instead ofthe more usual
split nut arrangement.This is shown in Fig. 9 whichillustratesthe
final form of leadscrew and clutch.
Adapting the leadscrewTo adapt the leadscrew, it was
necessary to turn down a plain portionat each end. This was done
by fitting.a brass bush in place of the tailstockbarrel and using
the tailstock bodyas a steady while the screw, held inthe four-jaw
chuck, was being turneddown. Both ends were thus treated,the small
portion of screw held in thechuck being cut off afterwards. Aplain
extension piece was then fittedand pegged at the tailstock end.
Itwas left on the long side to take ahandwheel and leave room for
possiblefuture developments.
The nut was secured to the saddleby means of a cage, bent up
from16-gauge sheet riveted to an anglebracket and attached by a
couple of
19 NOVEMBER 1959 421 MODEL ENGINEER
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into place and secured endways by Being restricted for bench
space,means of a tab, held by two screws it was felt that a
separate stand for theat the right-hand end. lathe would be a
valuable asset and as
A chip tray, Fig. 12, was made and a quantity of 20-gauge
galvanisedfitted between the lathe and the bench sheet offcuts were
to hand, a cabinetto help retain turnings and keep things stand was
designed to suit the sizestidy. available. The arrangement and
Allen screws. It allows for the nutbeing readily removed and at
thesame time restrains it from turningand moving endwise, see Fig.
10. Anapron or cover, Fig. 11, was alsofitted to keep swarf off the
leadscrewas far as possible. This was sprung
SHELF J
422 19 NOVEMBER 1959
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details of this are shown in Fig. 13and also in the photograph
of thecomplete machine.
With the exception of the 14-gaugebackplate and the angle feet,
it wasconstructed throughout from 20-gaugesheet fastened together
with 1/4 in.
galvanised gutterto be rigid and
bolts. It has provedyet is much lighter
plain bends being used. Although I
than cast or angle iron legs andhad the use of a hand-folding
machine,all bends can be done between two
provides ample storage space for toolsand equipment belonging to
the
angles. All pieces were formed,
machine.drilled, and finally bolted together.
The construction was simple, onlyThe countershaft angle pillars
werebolted to the cupboard sides through
19 NOVEMBER 1959 423 MODEL ENGINEER
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the 14-gauge plate, thus making asolid unit.
The object of the thicker plate forthe back of the cupboard was
tocarry the motor and so form a self-contained unit, but for a
number ofreasons this has not been done. Togive a professional
touch a monogramplate was fitted over the cupboarddoor. It was cut
from plywood withtwo of the plies cut away to leaveraised letters
and surround. It wasin fact a pattern for a casting, usedas the
casting.
The lathe was mounted with 1/4 in.plywood packings between the
feetand chip tray, and also between trayand cabinet top. It has
proved verysatisfactory, 1/2 in. thick rubber padsbeing inserted
between stand andfloor as it is used in an indoor work-
Changing power unitsAt this stage I acquired a Leyland
Barlow 6 in. power shaper with atraversing head, complete with
standand 1/2 h.p. motor. The first thing to bedone was to arrange a
drive to thelathe from the shaper motor and sofree the lathe motor
to work a sensitivedrilling machine which had been madeup in the
meantime from oddments.Up to this time all drilling had beendone on
the lathe.
With the advent of the shaper, anew cross-slide was made up in
steel,as shown in Fig. 14. It has a numberof tapped holes instead
of T-slots, andthe fitting of a topslide was nowessential. I wanted
to get ampleclearance between the tailstock andtopslide handle and
also to try out asquare guide in place of the usualV-pattern.
As I still had some of the firebarleft, a piece was machined as
detailedin Fig. 15. The slide pivots on a3/8 in. Allen screw, which
was alsoused as the main fixing, with an angle-plate attached to
the side, and curvedslots with setscrews to facilitatesetting for
taper turning. These areclearly shown in the photograph.
* To be continued on December 3
Saddle and topsIide with four-toolturret. Note offset topslide
screw
MODEL ENGINEERh.- J
424 19 NOVEMBER 1959
shop
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3-1/2 in. SCREWCUTTING LATHE Continued from 19 November 1959,
pages 422 to 424
Completing the vertical slide,back gear andchange wheels
By GEORGE B. ROUND
MODEL ENGINEER
THE topslide nut was formed in one piece with the keepplate and
brings the operating screw well clear of thetailstock. There is no
tendency to bind and the slideoperates smoothly and does not
require to be adjusted astightly as is necessary with a V-slide.
The success of thistopslide prompted the making up of the vertical
slide shownin Fig. 16. Construction was similar to the topslide,
exceptfor a single 1/2 in. bolt which is used to allow for
angularsetting 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
insixteenths rather than tenths of an inch. I am considering
theadvisability of changing to 20 t.p.i. so as to fit feed dials
graduatedin thous. But I feel that this thread is too fine for
feedscrews, anda lot of work is involved in making 10 t.p.i.
square-thread screwsfor all Slides.
A small electric motor from a Burroughs calculating machinehad
been obtainedto drive the drillingmachine before Ihad the shaper.
Thiswas fitted witha gearbox whichyielded a bronzeworm wheel
andsteel worm with aratio of approxi-mately 10-1/2 : 1. Italso had
a peculiarclutch arrangementfitting on a shaft ofthe same
diameteras the leadscrew ex-tension, which gavepromise of a
finefeed a la Pittler. The worm wasmade in one piecewith the shaft,
butwas detachable fromthe motor arma-ture? and fitted intoa piece
of 1 in. x14-gauge steel tube,secured to the endleg of the bed byan
odd aluminiumcasting. An ex-tension shaft allow-ed for the fitting
ofa pulley at the rearof the machine to
482 3 DECEMBER 1959
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View of the handandpower drive toleadscrew at tailstock end of
bed
VERTICAL
SLIDE
enable a power drive to be arrangedlater.
The worm wheel, together withthe centre portion of the
clutch,revolves loosely on the shaft, andthe outer portion, to
which a handleis fixed, was pinned to the shaft,thus driving the
leadscrew throughthe medium of a removable pin. Asthe worm has
seven starts this gearingis reversible. After a slow traverse
. with the handwheel or power feed,the saddle can be returned
for anothercut by means of the handle without
3 DECEMBER 1959
the necessity for disengaging theclutch. This is an advantage
whenscrewcutting as it is not essential forthe wormwheel to be
disconnectedfrom the leadscrew.
This was a fault on my 5 in. Pittler,where it was possible to
get the worm-driven screwcutting gears engaged atthe same time as
the worm-drivenfeed at the opposite end of the lead-screw. No doubt
Pittler fitted somesort of device to prevent this occurring,but if
so, it had been removed frommy machine. The picture on this
page
483
clearly shows this arrangement, to-gether with the finalised
form of powerdrive to give a longitudinal feed.
The vertical slide in use with theside and face milling cutters
of 3 in.and 4in. dia., emphasised the needfor a back gear. This was
also anecessity for screwcutting, which bythis time was deemed to
be essential.Screwcutting meant change wheels.These in turn, meant
some form ofindexing the blanks for cutting theteeth, all of which
I was determinedto produce on the lathe itself. Theseadditions were
more or less fittedconcurrently as the various require-ments were
dependent on one another.
Sorting out the gearsIn the search for a wormwheel
suitable for dividing, a broken circularknitting machine was
discovered. Thisprovided a worm and wheel, but of77 teeth-too large
for a dividinghead, but big enough to fit on themandrel of the
lathe. Although thiswas an awkward number for dividingpurposes, it
was better than nothing.Also discovered were two gearwheelsof 80
and 90 teeth and 1.5 modulepitch, of which size I had a
millingcutter: No 8 for 135 teeth and over.These, together with
some useful bitsand pieces from the knitting machine,were all the
ready-made parts avail-able.
Laying out these items in variousways. I suddenly realised that
bybreaking away from tradition aneffective backgear was possible.
Anarticle in MODEL ENGINEER by GeorgeGentry many years ago provided
thesolution, viz, an independent drivefor the mandrel when slow
speedswere required. Other additions (orcomplications) suggested
themselvesat the same time, and Fig. 18 showsthe final scheme, also
seen in the
MODEL ENGINEER
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second picture given here.The 80 T wheel would just fit on
the mandrel if a slight clearance wascut in the stiffening
angles of the head-stock, allowing the 90 T wheel to beused as an
idler wheel between an18 T wheel on the drive shaft, givinga ratio
in the region of 4-1/2 : 1.
At the same time the worm andwheel together with their cast
ironframe, were fitted with their integralbevel gear drive to give
an extra lowgear when desired, i.e., for circularmilling. Both were
driven by a3-3/4 in. dia. V-pulley, also off theknitting machine.
All this wascarried by two plates secured to achannel bracket
bolted to the boxleg at the rear of the headstock.
Fixing the 80 T gearBrass was used for the 18 T gear,
this being easier to cut in the cir-cumstances. With a little
touching upwith a fine file to remedy the defi-ciencies of the
shape of the teeth asleft by the cutter, the basic elementswere
complete. Fixing the 80 T gearto the mandrel was something of
aproblem, as owing to the solid bearingbushes for the mandrel,
raised keyscould not be fitted until the mandrelwas in place.
Furthermore, the key-way had to be cut by ha d. So as thepulley had
previously b een securedwith an Allen grubscrew, it wasdecided to
use the same method withthe addition of a dimple in the mandrelfor
greater security.
The wormwheel and 80 T gear were,therefore, bored a close fit to
themandrel and before final assembly,the pulley and wormwheel
weredrilled with clearance holes, and the80T gear with tapped holes
for four2 BA hex. head bolts to secure allthree together as one
unit.
These were assembled individuallyon the mandrel and the four
boltstightened up. At the same time anew 1 in. ball-thrust was
fitted. Itwas felt the arrangement deserved a
Reduction gear drive to mandrel
MODEL ENGINEER
REDUCTION GEAR UNIT
thrust race that was above suspicion,and that it would avoid the
necessityfor dismantling later to fit a new race.
Assembly went well, tightening upbeing a bit tricky owing to the
confinedspace. Finally, the whole unit wassolid with the mandrel,
and not untilthe reduction gearing had been in usefor some time was
it discovered thatthe grubscrew in the pulley had notbeen
tightened. Friction alone hadprovided an adequate drive due nodoubt
to slight inaccuracy in facingthe bosses.
Changing gearThe gear unit has proved most
effective and rigid in use, backgearbeing engaged by sliding the
90 Tidler wheel into mesh with mandreland drive shaft gears.
Withdrawinga spring-loaded pin in the counter-shaft V-pulley drives
the mandreldirect, two movements only beingnecessary as in normal
backgearing.The bevel gears for the extra lowratio gearing are only
in mesh whenrequired, being secured by a grub-screw. The frame
carrying the wormis secured by a locknut in the engagedor
disengaged positions,, this framebeing pivoted on the drive
shaft.
A detachable handle on the driveshaft allows the mandrel to be
turnedslowly by hand for special operations,and a 3 in. dia. pulley
screwed to theupper four-speed countershaft pulley
484
provides an adequate range of speeds.It is a reduction gear
rather than abackgear. The drive shaft is, of course,always
revolving whether the gear isin use or not-unless the belt
isremoved. But this is not a seriousdrawback. Provision has also
beenmade for fitting a handle at the topof the vertical worm
shaft.
To cut the gears a dividing head onthe direct indexing principle
was made.A gear cutting set-up on one of thechange wheels is shown
in the issuefor November 5. A block of duraluminwas used for the
body. Two inter-changeable spindles were used, onewith a 3/8 in.
dia., and one (as drawn)with a 5/8 in. dia. seating for the
gearblanks being cut.
Division plates, four in number sofar, are in 1/8 in. thick hard
aluminiumsheet, brass not being available.Steel was considered too
hard andtroublesome in which to drill a largenumber of small holes.
The alumin-ium has proved to be quite satisfac-tory.
I made a drilling spindle to drill theholes, the body being
formed from apiece of 1 in. dia. round brass bar,with a No 0 size
Jacobs chuck fittedto a taper on the spindle. When inuse, the
gadget is clamped on thetopslide and driven by a spring beltfrom
the 1/8 h.p. drilling machine motor,set up in a convenient
position.* To be continued on December 17
3 DECEMBER 1959
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3-1/2 in. SCREWCUTTING LATHEContinued from 3 December 1959,
pages 482 ta 484 Fitting the gearsand other parts By GEORGE B.
ROUND
M ACHINE-CUT gearwheels wereborrowed and fixed onan extension of
the lathemandrel to divide the plates duringdrilling, the plates
being held ona stud in the centre hole to ensureconcentric rings of
holes. Thesewere first spotted with a l/32 in.centre drill and then
opened outto 5/64 in. dia. using the sameset-up.
The drawing shows the details ofthe spring-loaded
plunger.dividing head has also been used onthe shaping machine,
with equalsuccess for gearcutting as on thelathe. The fly cutter is
mounted in atoolholder and fed downwards for eachtooth. This makes
an interestingvariation in the method of cuttingthe teeth involved
in a set of changewheels.
All change gears are 20 d.p., thisbeing settled by a Myford gear
of
65 T that was already to hand. Itwas used as a gauge in grinding
theflv cutter and it also meant one gearless to cut. A small amount
of easingwith a fine file was necessary for thesmaller gears to
ensure smooth run-ning. Various materials were used forthe gears,
brass, steel, cast iron andTufnol, and the complete set consistsof
20, rising by fives to 80, plus 63and 100 and duplicates of 20 and
30.All are 3/8 in. wide x 5/8in. bore, the100 wheel being made from
two 3/16 in,thick layers of Tufnol riveted together.
The cluster gearFig. 21 shows the arrangement of
the cluster gear, which is of the five-wheel type, a design I
wanted to tryout as it is considered to be free fromthe gathering
into mesh effect ofthe four-wheel pattern. The clustergears are of
Tufnol and the mandreland stud wheels of steel. All are of20 d.p. x
3/8 in. face and have provedexceptionally smooth in action.
MODEL ENGINEER
Change gears, feedshaft drive, reduc-tion and worm drive
544
Detailed in Fig. 22 is the pivot pinfor the cluster frame. The
leadscrewclutch 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 legto
limit the travel of the operatinglever.
Details of the quadrant and changegear studs are given in Figs.
26, 27and 28, these. again being in steel.The quadrant has a
separate arm andcurved slot for locking in position,an Allen screw
in the boss being usedfor temporary adjustment when mesh-ing the
gears. The boss is a separateitem riveted to the quadrant.
An odd shaped bracket from theknitting machine, together with
apair of dural bevel gears from ascrapped aero engine, finalised
thelongitudinal power feed. These werefitted as shown in Fig. 29
and Fig. 7.An aluminium packing block suitablycut to shape
furnished the bracketat the tailstock end of the bed. Thebackshaft
is 1/2 in. dia. x 16-gaugedrawn steel tube, with solid endspegged
to the tube, and a cork washer1 in. dia. recessed into one of the
bevelgears, making an effective clutch.
The pulleysA hardwood pulley, Fig. 30, is
fitted in place of the change wheel onthe stud- and drives by
means of aspring belt to the pulley on the back-shaft. This belt is
crossed to clearthe driveshaft for the mandrel reduc-tion gear. The
backshaft pulley is rubber and was a moulded castorwheel with an
inserted boss of steel,turned down and grooved for the beltand has
exceptional gripping power.
The lever fed tailstock barrel wasat some disadvantage since
drilling wasnow normally taken care of by aseparate machine. It had
insufficientcontrol over the drill for heavy drillingin the lathe
and so a new barrel,operated bv a handwheel and screw.as shown in
Fig 31, was made andfitted. It can, however, be withdrawnby
loosening two grubscrews and thelever-operated barrel can then
beinserted in a couple of minuteswhenever required.
With the change in driving motorscame the problem of
continuallystopping and starting. The 1/8 h.p.motor was dealt with
by a 5 amp.
17 DECEMBER 1959
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FEE D PULLEY
026
_ . _I - I ^ - - -. I
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tumbler switch in a metal case mountedon a length of steel
conduit bolted tothe cabinet stand at the right-hand end,[ME,
October 22]. This proved to beunsuitable for the 1/2 h.p. motor
andfor a short time, recourse was hadto flicking the round belt on
and offthe four-speed pulleys. This was amost unsatisfactory
arrangementwhich frequently resulted in the beltbreaking at the
fastener, usuallywhen one was in a hurry to completethe job in
hand.
Some form of clutch was obviouslycalled for, as owing to the use
of
a new four-speed pulley was turnedup from mahogany, and fitted
withball races so as to run freely on theshaft, and having a lining
piece of1/8 in. plywood on the large face. Tothis was glued a disc
of sheet cork,1/4 in. thick, to provide the friction drive.
A 6 in. dia. light alloy V-pulleywas fastened to a shouldered
steelsleeve and faced off true with the boreof the sleeve, and
suitably marked forreassembling. The 1 in. roller thrustrace
originally fitted to the mandrelwas placed between the pulley
andshoulder of the sleeve, with a light
rubber pads under the cabinet andshaping machine stands, a flat
beltwith fast and loose pulleys wasunsuitable since neither machine
wasfastened to the floor.
Trouble freeAs an experiment, the arrangement
shown in Fig. 32, and in section inFig. 33 was made up. After
morethan two years in use, it has provedcompletely effective and
trouble free,while at the same time being smoothin operation and
yet simple to makeup. The 1/2in. dia. lower shaft of
thecountershaft unit was replaced by oneof 5/8 in. dia. running in
die-cast alloybearings, located at each end bycollars, and having a
ball-thrustwasher at the right-hand end. Next,
MODEL ENGINEER
in conjunction with pulleys groovedto the same angle as for
A-size V-belts. These too, have proved to becapable of transmitting
all the powerrequired to drive the mandrel. Whilethe work the lathe
has done does not,of course, compare with factoryproduction speeds
and feeds, it hashandled work up to its maximumcapacity in
steel.
The machine incorporates a numberof controversial features, some
in-tentionally and some due to the factthat this was the only
available meansof construction. The parallel non-
aluminium casing to carry two with-drawal pins, the sleeve being
keyed tothe shaft, but free to slide endways.Another collar and a
spare valvespring completed the set-up.
A clutch lever made up from 5/8 in.x 1/8 in. flat bar, with a
leverage of4 : 1 was pivoted below the 1 in.thrust race. It was
controlled by ahandle having a boss with a pinarranged to give an
over-centremovement to a connecting link withthe top of the clutch
lever, the amountof axial movement at the clutch beingabout l/32
in. It has not been foundnecessary to modify the
originalarrangement and there is completeabsence of slip under any
load.
Round belts 1/4 in. dia. are used forboth main and reduced speed
drives,
546
adjustable bearings are perhaps themost outstanding matters of
con-troversy, but the fact remains thatthey have proved eminently
satis-factory with complete freedom fromchatter. The square edge
slides also,have been so successful that I preferthem, wherever
possible, to V-slides.They are much easier to make up andstill give
that smooth silky action sodesirable.
In use, the bed has proved to bevery rigid, the square tubular
sectionbeing, of course, highly resistant totorsional strains, and
possibly thestrongest form for this purpose. Myonly real regret is
that it is not severalinches longer, but that was notpossible under
the circumstances.
* Concluded next week
17 DECEMBER 1959
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Oval-fuming chuck in operation
THE general arrangement ofthe chuck together with de-tails of
the moving parts,are shown in Fig. 34, and Fig.35 shows details of
the fixed items.
The maximum amount of eccen-tricity that can be given to the
guidering is 1/2 in., giving a difference of1 in. between the major
and minoraxes of the ovals. This allows quitea wide range of work
to be done. Itwas constructed mainly of steel, thebackplate being
cut from a 5 in. dia.circle of 3/8 in. thick plate to which aboss
had been welded. After theguides and cover plates had beensecured
in position, the whole wasturned up to give a clean finish,
hencethe odd dimension of 4-15/16 in. for theoverall diameter.
Bright mild steel bar 2 in. x 3/8 in.was used for the slide and
a piece ofthe same material, sawn lengthwise,for the guide pieces.
The cut wasmade off-centre in order to allow forthe gib strip, and
at the same timekeep the chuck symmetrical and inbalance. The cover
strips were cutfrom 2 in. x 3/16 in. bright mild steelbar, and the
gib strip from 3/16 in.thick brass bar, the latter beinglocated
endwise by means of dimplesfor the ends of the adjusting
screws.
The screwed nose, of similar sizeto the mandrel nose, was shrunk
intothe slide, lightly riveted at the back,faced off flush and
drilled and reamedwith a 5/16 in. dia. hole for locating theslide
centrally on the backplate duringconstruction. This was done by
meansof a plug with a spigot, registering inthe same recess that
locates the back-plate to the mandrel nose.
A strip of tissue paper under eachcover plate provided just
enough
MODEL ENGINEER
3-1/2 in. SCREWCUTTING LATHEConcluded from 17 December 1959.
pages 544 to 546
Machining theguide ring andbase block
By GEORGE B. ROUND
PLAN IN PART SECTION
578 24 DECEMBER 1959
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clearance for a nice sliding fit. Beforefinally removing the
centre plug, ahole 1/8 in. dia. was drilled and reamedin a
convenient position so as tolocate the slide at any time in a
centralposition. Each guide was also fittedwith two dowels to the
backplate toensure permanent alignment.
To the back of the slide are fixedtwo shoe guides made of 3/4
in. x 3/16 in.brass T, with 3/8 in. thick mild steelpacking blocks
between them, to clearthe backplate.four 3/16 in. roundhead screws
in
Each is secured by
lightly counterbored holes, and finallylocated with dowel pegs
to preventlateral movement in operation. Theshoe is of 1/2 in-thick
Tufnol, the im-pregnated linen grade, two oppositeedges being made
parallel and thenbored exactly central to a nice runningfit on the
guide ring.
This guide ring was turned froma 2-1/2 in. mild steel shafting
collar,the grubscrew hole forming an ex-cellent oil pocket,
although larger
than necessary. It is clamped inposition in the fixed backplate
by a2 BA Allen screw, at exactly theheight of the lathe
centres.
The backplate rests at the bottomupon a base block shaped to
suit thebed section, and is secured to a clampbar of 1/2in. square
bright mild steelbar. This in turn rests upon, and isbolted to, a
lower clamp bar ofsimilar section provided with slotsscrewed to the
base block, thusproviding for the adjustment of theguide ring
relative to the axis of themandrel in a horizontal plane.
The base block is, of necessity,peculiar to the requirements of
thisparticular bed, and is made up frommild steel angle and channel
sectionswelded together and clamped to thebed in the manner of the
tailstock.This clamp also secures a similarblock carrying a small
hand-restwhen required for hand turning.
In operation, the chuck is smoothand easy running, taking good
cuts
without chatter. It was made up forplain oval turning only. For
orna-mental work an independent rotarymovement of the nose would
benecessary, but as this was not required,the extra rigidity of the
fixed nose wasconsidered a more desirable feature.
Other equipment, in addition tothat 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, anda sliding centre for taper turning.Side and
face milling cutters up to4 in. dia., and a special 2 in.
dia.facing cutter,, are held on stub mandrelsin the four-jaw chuck,
and a 6 in. x1/16 in. cutter is used for deep cutting-off or
slitting.
The four-jaw chuck, I would add, isstill accurate and in
first-class con-dition without shake in the jaws,despite 20 years
service. It is amazingvalue for the 25s. it cost in 1939.Cover
plates are fitted to the cross-
24 DECEMBER 1959 579
Below: Body of oval-turningchuck. It has been unscrewedto show
guide ring and shoe
MODEL ENGINEER
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B A C K P L A T E BASE
slide and the leadscrew gears toexclude swarf, and there are
alsoremovable shields at the back andfront of the chip tray, to
confineturnings, as far as possible, to the tray.
The machine and stand are finishedin an eau-de-nil green enamel
paint,making it easy to wipe down andclean, besides looking
effective. Theswitch which formerly did duty as astarter switch now
carries an electriclight mounted on a flexible hoIder. A40 w. bulb
at 12 v. is used, operatingthrough a transformer, to preventrisk of
shock through shorting ofcables.
With regard to cost, the only itemspurchased specially for this
machine,were the 1 in. ball-thrust race for 10s.,and the various
Allen screws and paintabout 35s. in all. My own scrapbox, and those
belonging to friends,provided the rest of the materials. q
GIANTS OF ENGINEERINGContinued from page 574
drying up of supplies first of the Balticpine from which they
were made andthen of the yellow Quebec pine whichwas substituted
for it.
When it is realised that Brunelsshipbuilding achievements were
largelycontemporaneous with his stupendousrailway works, some faint
realisationof his capacity for work and therange of his intellect
becomes possible.Between 1836 and his untimely death23 years later
he designed three greatsteamships,. each one in turn farexceeding
in tonnage anything everbefore attempted.
These were the Great Western,built of wood and propelled
bypaddles, the first real Atlantic liner,the Great Britain, built
of iron andscrew-propelled, and lastly the ill-starred Great
Eastern, also built ofiron but driven by screw and paddles.
MODEL ENGINEER
The paddle engines, four-cylinderdouble-diagonal oscillating
(there aremagnificent models in the ScienceMuseum), had a stroke of
14 ft, thelongest of any engine of which 1 canfind a record.
The screw engines of the GreatBritain were also of
double-diagonaltype (not oscillating) working upwardsand driving
the propeller shaft bymeans of a chain geared up 3 to 1, i.e.the
propeller shaft ran at three timesthe speed of the crankshaft.
TheGreat Western made no fewer than67 Atlantic crossings in eight
years.
All these ships, but particularlythe Great Eastern, were badly
handi-capped by inadequate dock andharbour facilities. An
outstandingcharacteristic of the Great Easternwas its marvellous
manoeuvrability.By the combined operation of paddlesand screw it
could turn practicallyabout 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 troubleswith its engines and
boilers,, none ofwhich could be directly attributed toBrunel,
finally broke his health andhis heart and he died on 15
September1859 when only 53 years of age.
Brunel was a man of immenselyforceful character and of
strongantipathies. He detested the pseudo-scientist and equally the
bone-headedself-styled practical man.
Perhaps the most fitting tribute tohim came from his friend and
colleagueDaniel (afterwards Sir Daniel) Goochwho wrote:
On the 15 September, I lost myoldest and best friend. By his
deaththe greatest of English engineers waslost.Facts in this
article have been taken
from Smiles Lives of the Engineers andZsambard Kingdom Brunel,
by L. T. C.Rolt (Longman and Co. Ltd.) 30s. q
24 DECEMBER 1959