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Sharp. Stones


Layout and Measuring Tool and their Makers


Rules, Squares, Straight Edges, Hack Saws, Screw Drivers and Wrenches - Shop Talks with the Young Mechanics by W. H. Vandervoort, 1897

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No tool in the machinistís kit is more often referred to than the steel rule.

Upon it he depends in making all ordinary measurements and for the setting of his calipers and dividers. In first image below is shown a standard steel rule or scale.  They are made in various lengths, from one to forty-eight inches, with any desired gradation, no exceeding 1-100 of an inch in fineness.

For shop work the gradation most used is eights, sixteenths, thirty-seconds and sixty-fourths, on the four corners of the scale.  A scale graduated sixteenths, thirty-seconds, sixty-fourths and one-hundredths is convenient, and the 100ths graduations will serve for measurements when required in decimals.

Where all the work is measured by fractions, however, the former is the safest ruling to use, as there is then no danger of inadvertently mistaking a tenth for an eighth division, etc. 

For this reason, rules graduated in twelfths and fourteenths should not find their way into the machinistís tool box, as he will not have occasion to use these divisions, and their presence will call for greater care in selecting the proper division, with the loss of time incident to changing ends with and turning over the rule in order to get at the division required.

The end graduation, as shown below, is frequently very convenient in taking measurements in recesses where the length of the scale would prevent the use of the regular graduation. Standard steel rules, as made by our leading makers, are remarkably accurate. 

To be sure, the length varies slightly with the changes in temperature, but these changes are not ordinarily great, and the material measured is usually affected about the same amount in the same direction; so we may feel assured that any errors arising from this source are well within the limit of the personal error of the operator in making a measurement.

The late refinements in the manufacture of steel rules have enabled the production of very accurate tempered ones on comparatively thin steel.  What we usually know as the standard rule, however, is graduated on thick steel, and is not tempered.  The tempered rules possess the decided advantage of resistance to wear.

An untempered rule is easily mutilated, and soon rounds its corners through wear, making its ends unfit for reference.  The tempered rules may be classed as heavy, tempered, semi-flexible and flexible.  The heavy are about about one-tenth; the tempered, one-twentieth; the semi-flexible, one-fortieth, and the flexible one-eightieth of an inch thick.  For general work the heavy or tempered will be found best suited.  The flexible are graduated on one side only, and are of value in measuring curved or irregular outlines.

In this connection it will be well to call attention to the gear rule show below.

Its application is in the sizing of gear blanks and where, by rule of thumb, two diameter pitches are added to the pitch diameter of the gear in obtaining the whole diameter.  Thus, if the pitch is No. 7 diametrical and the number of teeth 34, then the pitch diameter = 34-7=4-6/7 inches, and the blank or whole diameter = 4-6/7 +2/7=5- 1/7 inches, which can be taken directly from the scale.  This rule is of great convenience where many blanks for varying pitches and numbers of teeth are to be sized.

In the image to the left is shown a neat kink which will be found of value in taking measurement similar to the ones shown in the figure, as well as for setting inside calipers.  The hook may be quickly removed.  It is hardened, and in connection with a tempered rule forms a reliable tool.

In the image below is shown a standard steel square. This tool is made of cast steel, tempered and accurately finished.


The two sides of the angle are called the blade and the beam, the length of the blade being measured from inside the beam. The form shown above is preferable when the length of the blade exceeds eighteen inches, as it can be more readily repaired in case of accident.

Either of the methods shown in Figs. I and II may be used by the machinist in testing the accuracy of a square, the latter being the most exact of the two.

In Fig. I, A is a plane plate of iron with one edge, BC, perfectly straight.  The surface A should be smooth and true.  The square is first applied as shown at F and a file line DE scribed along its edge.  It is then reversed to position G, when, if the edge exactly lines with the ruling DE, the square is correct.  If, however, the edge and the line do coincide, the square is inaccurate by one-half the variation as shown.  Since this method depends for its accuracy on the eye of the operator it cannot be called and exact one.

The method shown in Fig. II reduced the amount of the personal error, since the eye detects readily the ray of light that passes through and exceedingly small opening.  In the figure the cylinder A, which has been ground accurately parallel and faced on the lower end slightly dishing, rests on a place surface, a standard surface plate being best suited to this purpose.  As the surface of the cylinder is at right angles to the surface of the plate the square can be compared with this angle by placing it as shown in the figure.

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