7/29/2019 [Metalworking] Model Engineer - Gauge Making With the Lathe

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WORKSHOP HINTS AND TIPS

Gauge making

with the lathe

As t he p rev ious a r t i c l eexplained, measuring withthe lathe can mean much

more on occasion than using themicrometercollars on feed screwsto obtain diameters and lengths offeatures on components.

The ordinary centre lathe, in fact,resembles a horizontal measuringmachine? with its straight bed andcentres in opposition. With simpleadaptation, it can be employed foractual measuring. Flat centres oranvils are substituted for the pointedones, then tests can be made oncomponents, and dimensions can beheld to a relatively high standard ofprecision. The process is aided by amicrometer collar on the tailstockbarrel, or by a graduated ring or sectoron the handwheel.

Greater precision is possible whenan indicator replaces the tailstockanvil, for in this application-as in allothers-an indicator has the advantageover human touch of uniform sensi-

tivity. Errors, moreover, are shownmagnified on its dial.

By GEOMETER

For a lathe which has no graduatedfeed to the tailstock, the topslideoffers an alternative mounting for ananvil or indicator, in opposition to theone in the headstock spindle. Ananvil can be screwed or pressed into aflat bar for mounting squarely on thetopslide, as at A. Any dimension, T,can then be obtained within thecapacity of the lathe, the graduated

feed on the topslide screw providingfine adjustment. The same can bedone with an indicator mounted on abar, its plunger at centre height andpointing straight at the spindle anvil.

Any of these ways of measuring canbe employed for checking simplegauges, which, themselves, can beused for a variety of purposes-formeasuring, for setting callipers, workand tools, for supporting parts, or forobtaining zero settings on indicatorswhich are used with the surface gaugeon the lathe or surface plate.

End gauges, which are the easiesttype to make, will perform all thesefunctions, providing a standard of pre-cision equal to those of many tool-

10 MAY 1962

rooms. The rods employed for themcan be either mild steel or silver steel;and for occasional use, either can beleft soft, though for lasting accuracymild steel should be casehardened atthe ends and silver steel should behardened and tempered. This treat-ment must be before gauges arefinished to length, which is done by lapping

Short gauges may be held in thefingers for measuring, but long onesshould be laid in V-supports, as on ameasuring machine. The object in thiscase is to avoid strain, though forvery precise measuring, it is just asimportant to avoid expanding a gaugewith the warmth of the hand. Twosupports are required for a gauge,each positioned about one-fifth of thetotal length of the gauge from theend. Diagram B shows a design madefrom angle and flat stock. The boltholes in the latter should be slotted sothat it can be adjusted to set gauges tocentre height.

As for the standard which is used in

gauge making, it must depend onwhat is available-a micrometer or avernier calliper. Assuming, however,it is only a 1 ft rule, a high standardof accuracy is possible. With care,the error on this length should notexceed 0.010 in. ; and it can be muchless.

As shown at C, two 6 in. gaugescan be made from the original one, U.These are V and W, each with half theoriginal error. From these, two morecan be made, X and Y, with the errorhalved again. Thus, it can be reducedto 0.0025 in. on 3 in., which is no

more than might obtain in makingthree 1 in. gauges from a micrometer.As shown, a sleeve joins pairs ofgauges for testing. Means of adjust-ment are also provided on gauges Vand X, so that only gauges Wand Yneed to be lapped.

Forhand lapping, a block is boredand faced, the gauge is pushed through,and the lap, charged with abrasive, isrubbed over the end. Adjustment isprovided, D and E, by taking packingfrom a clamp, or using an adjustingscrew. In lapping on the lathe, F, thegauge is pushed through a bar on toan abrasive-faced disc. For testinglength Z, it is tried between theanvil.

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0 ADjUSTI NG

SCREW

517 MODEL ENGINEER