The Micrometer - 6: Adjusting
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WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor.
Micrometers will need adjusting from time to time. The anvil and spindle faces wear down and the fit between the barrel nut and the spindle requires adjustment.
Before taking a measurement the tips of the micrometer should be cleaned by clamping lightly on a clean sheet of paper and pulling the paper from the tips. This removes all particles of dirt and dust.


Check for accuracy by closing the spindle gently against the anvil and note if the zero line on the thimble coincides with the zero on the spindle. Use the ratchet on the end of the micrometer to apply the closing pressure.

Now look at the alignment up close. When the micrometer tips are closed the "0" line on the thimble should be lined up with the reading line on the barrel.. This micrometer is off by quite a bit (it looks like maybe .0005 inch).

An adjusting spanner wrench like the one on the left probably came in the box with your micrometer. You will need it to adjust the error.
When describing the frame assembly on the previous page you will note that there was no mention of permanently fitting the barrel assembly to the frame. That is because the fit is fairly tight but not permanent. Using the spanner tool shown above left you can rotate the barrel reading line until it aligns with the thimble "0" line. It will take a little pressure to move it but it will turn into position.
Using the micrometer causes wear between the male threads on the spindle and the female threads in the barrel nut.

The same tool shown above can be used to squeeze the nut more snug against the sleeve threads.

Below is alternate method used on some micrometers. In this case a socket set screw is used to make adjustments.

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label: micrometer, history, anvil, thimble, spindle, frame, barrel, ratchet, adjustment, holding, handling, reading, vernier