A somewhat different type of sine bar is shown in Figure 22.3. It has two cylindrical plugs of equal diameter that are pressed into two holes that have been machined a precise distance L apart in the sine bar. The two plugs project out from this sine bar enabling precise measurements to be made on the projecting ends.

F IGURE 22.3 Plug-type sine bar supported on gauge blocks

In practice, these measurements are made over the top of the plugs with a vernier height gauge, usually in combination with a test type dial indicator. This sine bar may also be set at a given angle by resting the bar on the angle of the part to be measured as in Figure 22.4. While in this position, the H 1 and H 2 dimensions are determined by using the vernier height gauge set-up and measuring over the plugs. In either case, the angular relationship depends upon the distance L and the difference in the heights H 1 and H 2 , as shown by the simple formula:

F IGURE 22.4 Set-up for measuring the angle of a part with plug type sine bar

In Figure 22.5, a small (5-inch) sine bar is shown measuring the angle of a precision gauge block scriber attachment. The sine bar is tipped to the required angle by the gauge blocks placed under one of the rolls.

F IGURE 22.5 Measuring an angle on a surface plate using a sine bar, gauge blocks, and an electronic height gauge

E XAMPLE 22.1: Using a Sine Bar