vdoc

Chapter 7: A. Common Gages and Measurement Instruments 71
external measuring snap gage is shown in Figure 7.10f. It consists of a C-frame
with gauging members in the jaw of the frame. Figure 7.10g shows other types of
snap gages. Threads can be checked with thread plug gages, thread ring gages,
thread snap gages, or a screw-thread micrometer. Thread snap gages have two pairs
of gauging elements combined in one gage. With appropriate gauging elements,
these gages may be used to check the maximum and minimum material limit of
external screw threads in one pass. An example of a thread snap gage is shown
in Figure 7.10h. In some cases, special snap gages may be desired. The example in
Figure 7.10i illustrates the use of a special double-end snap gage for inspecting the
outside diameter of a narrow groove.
Spline Gages. The use of a spline gage is a common way of inspecting splined
workpieces prior to assembly. External splines are checked with internal-toothed
rings, whereas internal splines are checked with external-toothed plugs. Figure
7.10j shows the two basic types of fixed-limit spline gages: composite and sector
gages. Composite gages have the same number of teeth as that of the part.
Sector gages have only two sectors of teeth 180° apart. These gages are further subdivided
into go and no-go gages. View 1 of Figure 7.10j shows a go composite ring
gage, and a no-go sector ring gage is illustrated in view 2.
Screw-Thread Micrometer. A screw thread micrometer, such as the one shown in
Figure 7.10k, has a specially designed spindle and anvil so that externally threaded
parts can be measured. Screw-thread micrometers are generally designed to measure
threads within a narrow range of pitches. Thread plug gages are similar in
design to cylindrical plug gages except that they are threaded. They are designed
to check internal threads. Typical thread plug gages, such as those shown in
Figure 7.10l, consist of a handle and one or two thread gage members. Depending
on the size of the gauging member, the member can be held in the handle using
a threaded collet and bushing design (view 1), a taper lock design (view 2), or a
trilock design (view 3).
Templates. To check a specified profile, templates may be used. They may also be
used to control or gauge special shapes or contours in manufactured parts. These
templates are normally made from thin, easy-to-machine materials. An example
of a contour template for inspecting a turned part is shown in Figure 7.10m. To
visually inspect or gauge radii or fillets, special templates, such as those shown
in Figure 7.10n, may be used. The five basic uses of such templates are: inspection
of an inside radius tangent of two perpendicular planes (view 1), inspection
of a groove (view 2), inspection of an outside radius tangent to two perpendicular
planes (view 3), inspection of a ridge segment (view 4), and inspection of the
roundness and diameter of a shaft (view 5).
Screw-Pitch Gages. The pitch of a screw may be checked with a screw-pitch gage.
To determine the pitch, the gage is placed on the threaded part as shown in Figure
7.10o. A drawback of using screw-pitch gages is their inability to give an adequate
check on thread form for precision parts.
Special Gages. It is sometimes necessary to design special gages for checking special
part features such as square, hexagonal, or octagonal holes. Figure 7.10p shows
some special plug gages for checking the profile or taper of holes. As an inspection
Part II.A.2