Machining Fundamentals
72
There is no actual contact between the measur-
ing gage and wall of the bore being measured. The
bore measurement depends on the air leakage
between the plug and the hole wall. (The larger the
bore diameter, the greater the leakage.) Pressure
builds up and the measurement of the back pressure
gives an accurate measurement of the hole size.
Change in pressure (air leakage) is measured by
a dial indicator, a cork floating on the air stream, or
by a manometer (U-shaped tube in which the height
of fluid in the tube indicates pressure).
4.6.2 Electronic Gage
An electronic gage, Figure 4-43, is another type
of gaging tool used to make extremely precise
measurements. Electronic gages are comparison
gages: they compare the size of the work to a
reference size. Some are calibrated by means of
master gage blocks and others use replaceable
gaging probes. These instruments measure in both
US Conventional and SI Metric units.
4.6.3 Laser Gaging
A laser is a device that produces a very narrow
beam of extremely intense light. Lasers are used in
communication, medical, and industrial applica-
tions. Laser is an acronym for light amplification by
stimulated emission of radiation.
The laser is another area of technology that has
moved from the laboratory into the shop. When
employed for inspection purposes, it can check the
accuracy of critical areas in machined parts quickly
and accurately. Refer to Figure 4-44.
4.6.4 Optical Comparator
The optical comparator uses magnification as a
means for inspecting parts, Figure 4-45. An
Figure 4-41. Digital air gages are available with either
US Conventional or SI Metric readouts. They can check either
inside or outside diameters. A—An air gage set up to inspect an
internal dimension. The master ring shown with the gage is
used to set zero on the readout. B—This gage has an air fork,
which is used to check hard-to-reach diameters, such as crank-
shaft journals. (Federal Products Company)
Nonadjustable
equalizing jet
Zero setting valve
Cushioned
and jewelled
indicating
movement
Master
Gaging plug
Nonadjustable
master jet
Pressure
regulator
Filter
Air
supply
Master
pressure
gage
Differential
pressure
meter
Figure 4-42. This diagram illustrates the operation of an air
gage.
A
B