--

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

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

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

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

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

- DE T A I L O F S A D D L E

:I 3: __... .; ;

__ ._. _. _ . .._ -..-. _...I+- ?-

I 4 B O X L E G

-

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

,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

_--

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

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

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

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

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

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

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

FEE D PULLEY

026

_ . _I - I ^ - - -. I

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,

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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

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

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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

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

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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.

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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