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82 Part II: Metrology
no pressure between the two, which causes wear, and the gage head may have a
large allowance for any wear that does occur. The flowing air also helps keep surfaces
clean.
The lack of contact makes air gauging particularly suitable for checking highly
finished and soft surfaces. Because of its loose fit, a pneumatic gage is easy and
quick to use. An inexperienced inspector can measure the diameter of a hole to 25
mm (.000001 in.) in a few seconds with a pneumatic gage. The same measurement
(to 25 mm or .001 in.) with a vernier caliper by a skilled inspector may take up to
one minute. The faster types of pneumatic gages are adequate for high-rate automatic
gauging in production.
Part II.B.3
SUMMARY OF GAGE USES AND APPLICATIONS
Table 8.1 provides a useful summary of the gages presented in Chapters 7 and 8
and their uses and applications.
Table 8.1 Summary of commonly used gages and their applications.
Gage
Steel rule
Depth rule
Vernier caliper
Digital-reading
caliper
Vernier
height gage
Digital
micrometer
Dial indicator
Optical
comparator
Gage block
Uses and applications
Used effectively as line measuring devices, which means that the ends of a
dimension being measured are aligned with the graduations of the scale,
from which the length is read directly.
Used for measuring the depth of slots, holes, and so on.
Typifies instruments using the vernier principle of measurement. Outside
dimensions are measured between the lower jaws; inside dimensions over
the tips of the upper jaws.
Provides LCD readouts in either millimeters or inches and operates by a
microprocessor-based system. Capable of retaining a reading in the display
when the tool is used in an area where visibility is restricted.
Similar to a vernier caliper except that the fixed jaw has been replaced
by a fixed base, and the sliding jaw may have a scriber attached to it for
layout work, or a dial indicator for measuring or comparing operations.
Used in measuring diameters, thicknesses, inside dimensions, heights,
and outside dimensions.
Used for applications such as measuring heights, flatness, diameters,
and so on.
Used for measuring complicated or difficult shapes and other
configurations.
Dimensional measurement standards that are used to calibrate other
measuring devices. They come in sets of different grades depending on
the desired measurement accuracy required. Each set has many blocks of
incremental lengths. These blocks are stacked together (wringed) to build
a desired length.
Continued