Machinery's Handbook, 31st Edition
694 Sine-Bars has several through holes to reduce the weight. In the making of the sine-bar shown in Fig. 2, if too much material is removed from one locating notch, regrinding the shoulder at the opposite end would make it possible to obtain the correct center distance. That is the reason for this change in form. The type of sine-bar illustrated by Fig. 3 has the cylindrical disks or plugs attached to one side. These differences in form or arrangement do not, of course, affect the principle governing the use of the sine-bar. An accurate surface plate or master flat is always used in conjunction with a sine-bar in order to form the base from which the vertical measurements are made.
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Fig. 3. Fig. 4. Setting a Sine-Bar to a Given Angle.— To find the vertical distance H for setting a sine-bar to the required angle, convert the angle to decimal form on a pocket calculator, take the sine of that angle, and multiply by the distance between the cylinders. For example, if an angle of 31 degrees, 30 minutes is required, the equivalent angle is 31 degrees plus 30 ⁄ 60 = 31 + 0.5, or 31.5 degrees. (For conversions from minutes and seconds to decimals of degrees and vice versa, see page 103). The sine of 31.5 degrees is 0.5225, and multiplying this value by the sine-bar length gives 2.613 inches for the height H , Fig. 1 and Fig. 3, of the gage blocks. Finding Angle when Height H of Sine-Bar is Known.— To find the angle equivalent to a given height H , reverse the above procedure. Thus, if the height H is 1.4061 in., dividing by 5 gives a sine of 0.28122, which corresponds to an angle of 16.333 degrees, or 16 degrees 20 minutes. Checking Angle of Templet or Gage by Using Sine-Bar.— Place templet or gage on sine-bar as indicated by dotted lines, Fig. 1. Clamps may be used to hold work in place. Place upper end of sine-bar on gage blocks having total height H corresponding to the re- quired angle. If upper edge D of work is parallel with surface plate E , then angle A of work equals angle A to which sine-bar is set. Parallelism between edge D and surface plate may be tested by checking the height at each end with a dial gage or some type of indicating comparator. Measuring Angle of Templet or Gage with Sine-Bar.— To measure such an angle, ad- just height of gage blocks and sine-bar until edge D , Fig. 1, is parallel with surface plate E ; then find angle corresponding to height H of gage blocks. For example, if height H is
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