(a) Spring caliper.
1. The spring caliper is available in sizes from 2 to 8 inches. The
friction of the adjusting nut and screw works against the tension of the spring
which holds the legs in any set position. This type of inside caliper is known as
the toolmaker's spring caliper.
2. Thread spring calipers are used to measure diameter and distances
in tapped holes. The ends of the legs of thread calipers are shaped to a fine
point so that exact contact may be made between threads.
(b) Firm joint caliper. The firm joint type is available in a number of
sizes from 3 to 24 inches. This type of caliper is equipped with a nut and stud
that provide sufficient friction to hold the legs in any set position. Some of
this type caliper are equipped with an adjusting screw for fine adjustments.
(c) Transfer firm joint caliper. Inside transfer firm joint calipers
are shaped for inside measurements and are used for measuring recesses where the
setting cannot be transferred to a scale directly because the legs must be
collapsed to remove them from the work.
(3) Use of calipers.
Either the caliper is set to the dimension of the work and the dimension
transferred to a scale, or the caliper is set on a scale and the work machined
until it checks with the dimension set up on the caliper. To adjust an outside
caliper to a scale dimension, one leg of the caliper should be held firmly against
one end of the scale and the other leg adjusted to the desired dimension (A, fig
51). To adjust the outside caliper to the work, open the legs wider than the work
and then bring them down to the work. A sense of feel must be acquired to use
calipers properly. This comes through practice and care in using the tool to
eliminate the possibility of error. Always position the caliper properly on the
axis of the work (B, fig 51).
Using outside calipers.