WORKSHOP HINTS AND TIPS

M EASURING is often performedwith a modern lathe in thenormal course of machin-

ing. The topslide feed screw andalso the cross-slide feed screw,have micrometer collars. Theleadscrew of a small lathe some-times has a graduated handwheel,and it is not unusual for a tailstockbarrel to have a similar graduatedhandwheel or a micrometer collar.

With these it is possible to machinemany short steps, shallow recesses,overall lengths, widths of flanges,and so forth, to within a few thou ofan inch, which is an acceptablestandard for parts that have no statedtolerances to their dimensions.

An example of general procedure isto machine a piece of bar with a shortdiameter to a shoulder, using thetopslide and cross-slide feedscrews.

First, the topslide collar is set tozero, then the saddle is moved for thetool to take a facing cut on the bar,

B y G E Q M E T E R

after which the saddle is locked to thebed, or is located by engaging theleadscrew nut. When the facing cuthas been taken, the topslide screw isused to obtain the distance to theshoulder, reading on the micrometercollar.

To obtain the diameter, a check ismade on the bar-by micrometer-following a trial cut. This shows howmuch there remains to machine. Halfthe amount is taken on the cross-slidemicrometer collar, after it has beenset to zero, for the tool cuts on aradius, whereas the check is over adiameter.

With this procedure the lathe isused not only to turn, but to measurethe job: and the result is obtained ina shorter time and to greater precisionthan when working haphazardly.Many variations are possible of thebasic idea, here given in the simplestterms.

These typical uses, however, are notall the measuring operations of whicha lathe is capable, for in its bed andits headstock and tailstock. it has theelements of a measuring machine.With a pair of flat-ended “ centres ”

3 MAY 1962

Measuring with the lathe

as anvils, one in the spindle, the otherin the tailstock barrel, as at A, a lathecan be used for measuring parts, orfor holding dimensions for verification.

A motorist who has a lathe, but nolarge micrometer, can check a set ofpistons more accurately than withcallipers, using feeler gauges to testvariations. With callipers or simpleadjustable end gauges, cylinders canbe tested for ovality and taper, andthe dimensions brought to the latheto reveal variations.

In a similar way, a lathe, functioningas a large micrometer or rigid callipers,will hold dimensions that are setwith inside micrometers-which is avaluable function when long endgauges are being lapped to length,with frequent checks.

For any of these measuring opera-tions, it is an advantage for thetailstock to have a micrometer collar-or some other means by whichthous of an inch can be read off,even though only through a shortrange. Lacking a micrometer collar,a simple solution to the problem is tomark the handwheel, and use apointer like that of a surface gaugeto it. For instance, if a range of0.005 in. is needed, two marks can bemade on the handwheel, one with,the other without, a feeler gauge0.005 in. thick at the anvils.

A better way is to mount a gradu-ated ring on the handwheel, or a ringon which a graduated sector can beclipped, as at B. Such a ring can becut out with pointed tools from sheetsteel which has been screwed to woodbacking on the lathe faceplate. Foruse, the ring should be secured to thehandwheel by two countersunk screwsin tapped holes. The sector can bemade as shown in detail-the plate 1,packing 2, clip 3, all from sheet steeland held together by two countersunkscrews and nuts. With the sectorclipped on the ring, it can be adjustedafter the anvils have been set; andwith the pointer of a surface gaugebrought to its scale, measurementscan be made through a short range.

Short range measurement, coupledwith sensitivity, is obtained with anindicator mounted in the tailstock;diagram C shows an example of thisarrangement. It is particularly helpfulfor making sets of end gauges ofequal length, like the pairs at D. q

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SPINDLE TAlLSTOCK

I BLOCKI

LATHE BED

INDICATOR TAILSTOCK

CLAMP SHANK

MODEL ENGINEER