USE/CARE OF HANDTOOLS & MEASURING TOOLS - OD1621 - LESSON 3/TASK 1
changing settings by hammering instead of by loosening a clamping screw or
nut, bearing down too hard when scribing with a divider or trammel, wearing
measuring surfaces unnecessarily by using a heavy measuring pressure. Apply
a protective film of oil to tools when not in use.
The accuracy of the Vernier caliper
depends on the condition of fit of the sliding jaw, and the wear and
distortion in the measuring surfaces. The fit of the sliding jaw should be
such that it can be moved easily and still not have any play.
It may be
adjusted by removing the gib in the sliding jaw assembly and bending it.
The function of the gib is to hold the adjustable jaw against the inside
surface of the blade with just the right pressure to give it the proper
Wear on the jaws of the Vernier caliper is mostly at the tips
where most measurements are made.
Some of this wear may be taken up by
adjusting the Vernier scale itself.
This scale is mounted with screws in
elongated holes which permit it to be adjusted slightly to compensate for
wear and distortion.
When the error exceeds 0.0002 inch, either in
parallelism or flatness, the caliper should be returned to the manufacturer
for reconditioning. Wear on the jaws can best be checked by visual means
and by measuring rolls or rings of known dimensions.
Micrometers are used for measurements requiring precise
They are more reliable and more accurate than the calipers
discussed in the preceding paragraph.
b. Types of Micrometers.
sizes, depending upon the purpose for which they are to be used. They all
have a precision screw adjustment offering great measuring accuracy.
(1) Micrometer Caliper.
(a) The micrometer caliper (figure 190 on the following page) is
the most common type. It has a range of 0 to 1 inch and is graduated to
read in thousands of an inch or in units of the Metric system, from 0 to 25
millimeters by hundredths of a millimeter. It may or may not have: