Then, place the squaring head of a combination

square, as shown in view B. Secure the scale so the

end is in contact with the surface of the plate. Move

the surface gauge into position.

A sine bar is a precisely machined tool steel bar

used with two steel cylinders. In the type shown in

figure 2-25, the cylinders establish a precise distance

of either 5 inches or 10 inches from the center of one

to the center of the other, depending upon the model

used. The bar itself has accurately machined parallel

sides, and the axes of the two cylinders are parallel to

the adjacent sides of the bar within a close tolerance.

Equally close tolerances control the cylinder

roundness and freedom from taper. The slots or holes

in the bar are for convenience in clamping workpieces

to the bar. Although the illustrated bars are typical,

there is a wide variety of specialized shapes, widths,

and thicknesses.

The sine bar itself is very easy to set up and use.

You do need a basic knowledge of trigonometry to

understand how it works. When a sine bar is set up, it

always forms a right triangle. A right triangle has one

90-degree angle. The base of the triangle, formed by

the sine bar, is the surface plate, as shown in figure

2-25. The side opposite is made up of the gauge

blocks that raise one end of the sine bar. The

hypotenuse is always formed by the sine bar, as

shown in figure 2-25. The height of the gauge block

setting may be found in two ways. The first method is

to multiply the sine of the angle needed by the length

View A of figure 2-24 shows a surface gauge

of the sine bar. The sine of the angle may be found in

any table of natural trigonometric functions. For

V-block combination used to lay out a piece of stock.

example, if you had to set a 10-inch sine bar to check

To set a surface gauge for height, first clean the top of

a 30°5´ angle on a part, you would first go to a table of

the surface plate and the bottom of the surface gauge.

2-12

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