USE/CARE OF HANDTOOLS & MEASURING TOOLS - OD1621 - LESSON 3/TASK 1
which is graduated to control measurements to a limit of 0.0001 inch.
Measuring a ball at several points over the surface of the anvils will show
up any error in parallelism.
Parallelism can be tested by means of two
balls mounted in an aluminum holder. If the anvils are in error more than
the allowable maximum, the micrometer should be returned to the manufacturer
for repair.
(9) In adjusting a micrometer to read correctly, the thimble is not
set to 0, when the anvil is in contact with the spindle, but is set at some
other dimension, to distribute the error.
For example, if a micrometer
screw had an accumulated error of 0.0003 inch in the length of its travel,
and it were set correctly at 0, it would be off 0.0003 at 1 inch. However,
if the micrometer were set correctly in the center of its travel, it would
be 0.00015 under at 0 and 0.00015 over at 1 inch, which is a much better
condition. Because a micrometer does not return exactly to 0 when anvil and
spindle contact does not mean that it is not adjusted properly. Turn the
friction sleeve with a small spanner wrench to compensate for minor wear on
the anvil and spindle or on the screw, as shown in figure 196 on the
following page.
7.
Miscellaneous Measuring Gages
a. Description and Purpose.
(1) Thickness (Feeler) Gages.
These gages are made in leaf form,
which permits the checking and measuring of small openings, such as contact
points, narrow slots, etc. They are widely used to check the flatness of
parts in straightening and grinding operations and in squaring objects with
a tri square.
(2) Wire and Drill Gages.
The wire gage is used for gaging metal
wire;
a similar gage is used to check the size of hot and cold rolled steel,
sheet
and plate iron, and music wire.
Drill gages determine the size of
drill
and indicate the correct size of drill to use for a given tap size.
Drill
number and decimal size is also shown in this type gage.
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