The design of vernier caliper gages
Caliper gages are made in different lengths, starting with a useful
range of about 5 inches, and are available in lengths of uo to 48
inches, or, exceptionally, ever longer. The depth of the jaw also
varies, although not in a linear relationship with measuring
range.
The form of the jaws may be designed for measuring external surfaces
only, or can be provided with features permitting internal
measurements as well. Measurements on interal surfaces are made
either by inside gaging jaw tips or directly, by knife dege
auxiliary jaws that can pass each other along a common mating plane.
When measuring inside distances with the jaw tios, the combined
thickness of the two tips must be added to the indicated dimension,
unless the beam has separate graduations for outside and inside
measurements.
Vernier calipers intended for general applications are made with
plain sides, usually equipped with internal locking springs, whereas
for precision measurements the combination type slides are
preferred. The latter slides have a sliding clam that can be locked
in position and serves as the nut for a fine adjusting screw acting
on the measuring slide.
Some caliper gages have a depth gage tongue. This feature has some
usefuless for rapid measurements, although the precision of depth
gaging by this means is not considered to be equivalent to
measurements between the jaws of the same instrument.
The purpose of the locking screw on the slide is to maintain a fixed
jaw opening for the sequential measurement of parts with the same
nominal size, using the caliper as a snap gage. Calipers must not,
however, be considered equicalent substitutes for snap gages,
primarily because the setting accuracy of a vernier caliper is
inferior to the gage maker tolerances to which snap gages are made.
The locking screw should be on the top side of the slide in order to
draw the slide against the lower edge of the beam. The end of the
locking screw must not act directly on the beam, but should transmit
the locking force through an appropriate insert strip.