THE LATHE

I T IS A great convenience, evenon a simple lathe, to be ableto mark round components

with the commonly-required num-bers of divisions, such as four orsix, as are necessary when makingsquares and hexagons; and to makeother numbers of equal spacingsin a neat and regular manner, suchas to provide serrations on theedges of small bosses and knobsby which a finger grip can beobtained on fittings.

It is true, square and hexagonmateterial can be obtained in rangesof standard sizes; but these do notcover all requirements-such as anexceptionally large size, or if a fittingis needed with a circular flange largerthan the hexagon, or if a square orhexagon is required on the end ofa shaft for key or spanner manipu-lation.

To make squares or hexagons to ahigh degree of precision, milling is,of course, necessary.; but for generalpurposes careful fihng-checking bymicrometer if desired is quite satis-factory. When the lathe has meansof dividing, the material is machined

. slightly larger than the size over thecorners, a pointed tool being mountedsideways in the toolholder and settouching the work.

Using four-jaw chuckAt each located position the tool

is traversed by saddle or topslide,leaving a scribed line. To producethe flats, the material between thelines is filed away, the job beingremoved from the chuck and held inthe vice, still on the bar or in softjaws to avoid damage.

When equipment includes a four-jaw chuck and the jaws overlap theflat surface of a bed, squares can bemarked by holding each jaw to asupport bar, as at A. Such a bar canbe from round mild steel, say about5/8 in. dia., its length having beenobtained by checking with insidecalipers from the bed to the under-

21 FEBRUARY 1957

sides of a pair of iaws when these arehorizontal: The bar should be reason-ably to length, and it can be usedeither side of the bed, but on one sideonly for one job.

Another method, applicable in theabsence of a four-jaw chuck and alsoto work between centres is to clampa straight bar to the work, as at B .Distances X-Xl can be equalised witha surface gauge or scribing block anda mark made on the work with thetoo!; then the bar can be set horizontalagain, after rotating half a turn, formaking the second mark.

Quarter markings are made withthe bar set vertically with a squarefrom the bed. Pressure can be kepton the work from the tailstock toprevent movement.

Quicker methodMuch more speedy and wider in

scope, however, are drilled backplates,as at C, in conjunction with a simpleplunger device for holding. Indexingfor drilling can be done from achange gear which can be mountedon a mandrel in the chuck, key-pinnedand held by a setscrew. A locatingbar in the toolholder fits between thegear teeth, as at D.

When there are two chucks, 12spacings on one backplate and 40on the other will give the followingdivisions most commonly needed: onthe first, 2, 3, 4, 6, 12; on the second,2, 4, 5, 8, 10, 20, 40. The first can beobtained from a 48 or 60 tooth gear;the second from a 40 or 80 tooth gear.

The guide for a drill about 1/8 in. dia.should be from silver steel, andhardened. A countersunk screw fixesit to a mild-steel bar which is mountedfrom the back on a block or wall, orfrom the bench or stand at the frontof the bed, as at E.

For a bench lathe, indexing can beas at F, a cross-bracket fixed behindthe lathe carrying a pivoted bar witha silver steel pin. Normally, the barholds by its own weight, or a wing-nut and screw can be fitted at Y fortightening.

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AMPED

ON

LOCATING

M O D E L E N G I N E E R