Lesson 1/Learning Event 1
b. Oil the micrometer in only one place--the screw.
If storing a
micrometer for long periods of time, however, cover it with a light
film of oil and wrap it in oiled paper.
c. Never roll the thimble along the hand or arm. Likewise, never hold
the thimble and twirl the frame to open or close the micrometer.
This misuse causes excessive wear on the screw.
d. Before using a micrometer, wipe it off and pull a piece of paper
between the anvil and the end of the spindle.
e. The micrometer should operate freely with no play in its travel. If
a micrometer has play, or if it binds, it should be returned to the
manufacturer for reconditioning. (Play is caused by abuse or uneven
f. Check the micrometer screw periodically with a precision gage block
in at least four places other than zero to verify its accuracy.
Simply measure a selected group of blocks ranging from 0 to 1 inch.
g. Clean the micrometer mechanism whenever it becomes gummy, contains
abrasive grit, or needs to be adjusted.
Use an approved cleaning
h. Test the accuracy of the micrometer periodically. When the faces of
the spindle and anvil become worn and are no longer flat and
parallel to each other, measurement errors can result.
tolerance must not exceed 0.0002 inch on a micrometer graduated to
control measurements to a limit of 0.001 inch and must not exceed
0.00005 inch in a micrometer which is graduated to control
measurements to a limit of 0.0001 inch. Measuring a ball at several
points over the surface of the anvil will reveal any error in
parallelism. Parallelism can be tested using 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.
i. Adjust the micrometer thimble setting periodically. 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 dimension
to distribute the error. For example, if a micrometer screw has an
accumulating error of 0.0003 inch in