PRECISION MEASURING AND GAGING - OD1642 - LESSON 1/TASK 2
2 If the shaft is not oversize, the first button (3) (view B)
on the gage will pass over it easily.
3 Move the gage to the position shown in view C. If the NO
GO button (4) stops the gage, the shaft is within limits. However, if the
gage can be rocked further, as shown in view D, then the part diameter is
too small, since it has passed over the NO GO button. This is known as a
reject.
c.
Fixed Gages. Fixed gages cannot be adjusted. They can generally be
divided into two categories, graduated and nongraduated. The accuracy of a
machinist's work, when using fixed gages, will depend on the ability to
determine the difference between the work and the gage.
For example, a
skilled machinist can take a dimension accurately to within 0.005 of an inch
or less when using a common rule. Practical experience in the use of these
gages will increase ones ability to take accurate measurements.
(1) Rules.
(a) Steel Rule.
The steel rule with the holder set (figure 18,
view A, on the following page) is convenient for measuring recesses. It has
a long tubular handle with a split chuck for holding the ruled blade. The
chuck can be adjusted by a knurled nut at the top of the holder, allowing
the rule to be set at various angles. The set has rules ranging from 1/4 to
1 inch in length.
(b) The Angle Rule. The angle rule (figure 18, view B) is useful
in measuring small work mounted between centers on a lathe. The long side
of the rule (ungraduated) is placed even with one shoulder of the work. The
graduated angle side of the rule can then be positioned easily over the
work.
(c) The Keyseat Rule.
Another useful measuring device is the
keyseat rule (figure 18, view C).
It has a straightedge and a 6 inch
machinist's type rule arranged to form a right angle square. This rule and
straightedge combination, when applied to the surface of a cylindrical
workpiece, makes an excellent guide for drawing or scribing layout lines
parallel to the axis of the work. This
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