PRECISION MEASURING AND GAGING - OD1642 - LESSON 1/TASK 2
(2) The term "gage", as used in this lesson, identifies any device
which can be used to determine the size or shape of an object. There is no
significant difference between gages and measuring instruments.
They are
both used to compare the size and shape of an object against a scale or
fixed dimension.
However, there is a distinction between measuring and
gaging which is easily explained by an example. Suppose that the machinist
is turning a workpiece in the lathe and wants to know the diameter of the
workpiece.
He would take a micrometer, or perhaps an outside caliper,
adjust its opening to the exact diameter of the workpiece, and determine
that dimension numerically. On the other hand, if he wants to turn a piece
of work down to a certain size without frequently taking time to measure it,
he could set the caliper at a reading slightly greater than the final
dimension desired; then, at intervals during the turning operations,
measure, gage, or "size" the workpiece with the locked instrument.
After
the workpiece dimension has been reduced to the dimension set on the
instrument, he would measure the workpiece to the exact dimension desired.
b.
Adjustable Gages.
Adjustable gages can be adjusted by moving the
scale or by moving the gaging surface to the dimensions of the object being
measured or gaged. For example, on the dial indicator, the face is adjusted
to align the indicating hand with the zero point on the dial. On verniers,
the measuring surface would be moved to the dimensions of the object being
measured.
(1) Dial Indicators.
(a) Dial indicators are used by the machinist in setting up
workpieces in machines and in checking the alignment of machinery.
Proficiency in the use of the dial indicator requires a lot of practice; the
more one uses it, the more it will aid in doing more accurate work.
(b) Dial indicator sets (figure 2 on the following page) usually
have several components that permit a wide variation of uses. The contact
points allow the indicator to be used on different types of surfaces. The
universal sleeve permits flexibility of setup.
The clamp and the holding
rods permit setting the indicator to the work. The hole attachment is used
to indicate the variation, or run out, of the inside surfaces of holes and
the
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