PRECISION MEASURING AND GAGING - OD1642 - LESSON 1/TASK 2
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.
2 The sine bar itself is very easy to set up and use.
One
does not need to have a basic knowledge of trigonometry to understand how it
works.
When a sine bar is set up, it always forms a triangle.
A right
triangle has one 90ƒ angle. The base of the triangle formed by the sine bar
is the surface plate (figure 25). The side opposite is made up of the gage
blocks that raise one end of the sine bar. The hypotenuse is always formed
by the sine bar. The height of the gage block setting may be found in two
ways. The first method is to multiply the sine of the angle needed by the
length of the sine bar. The sine of the angle may be found in any table of
trigonometric functions. The second method is to use a table of sine bar
constants. These tables give the height setting for any given angle (to the
nearest minute) for a 5 inch sine bar. Tables are not normally available
for 10 inch bars because it is just as easy to use the sine of the angle and
move the decimal point to the right.
FIGURE 25.
SETUP OF THE SINE BAR.
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