4.1 SINE BAR AND SINE PLATE CALCULATIONS

Sine Bar Procedures. Referring to Figs. 4.1a and b , find the sine bar setting height for an angle of 34 25 ? using a 5-in sine bar.

Set the sine bar height with Jo-blocks or precision blocks to 2.826 in.

From this example it is apparent that the setting height can be found for any sine bar length simply by multiplying the length of the sine bar times the natural sine value of the required angle. The simplicity, speed, and accuracy possible for setting sine bars with the aid of the pocket calculator renders sine bar tables obsolete. No sine bar table will give you the required setting height for such an angle as 42 17 ?26 ?, but by using the calculator procedure, this becomes a routine, simple process with less chance for error.

Method

1. Convert the required angle to decimal degrees.

2. Find the natural sine of the required angle.

3. Multiply the natural sine of the angle by the length of the sine bar to find the bar setting height (see Fig. 4.1b).

   
   Figure 4.1: ( a) Sine bar. ( b) Sine bar setting at 34 25 ?.

Formulas for Finding Angles. Refer to Fig. 4.2 when angles ? and are known to find angles X, A, B, and C.

Figure 4.2: Finding the unknown angles.

NOTE.

Formulas and Development for Finding True and Apparent...