Maintenance of Micrometers.

Precision Measuring and Gaging
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Maintenance of Micrometers.

A micrometer should be checked for zero

setting (and adjusted when necessary) as a matter of routine to ensure that

reliable readings are being obtained. To do this, proceed as follows:

(1) Wipe the measuring faces with a clean soft cloth, making sure

that they are perfectly clean.

Use the same moderate force that is

ordinarily used when a measurement is taken and bring the spindle into

contact with the anvil.

The reading should be zero; if it is not, the

micrometer needs further checking.

(2) If the reading is more than zero, examine the edges of the

measuring faces for burrs.

Should burrs be present, remove them with a

small slip of oilstone.

Clean the surfaces again, then recheck the

micrometer setting for zero.

(3) If the reading is less than zero, or if a zero reading is not

obtained after making the correction described in (2) above, the relation

between the spindle and the thimble will have to be adjusted. The method

for setting zero differs considerably between the makes of micrometers.

Some makes have a thimble cap which locks the thimble to the spindle; some

have a rotatable sleeve on the barrel that can be unlocked; and some have an

adjustable anvil.

(4) Methods For Setting Zero.

(a) To adjust the thimble-cap type, back the spindle away from the

anvil, release the cap with, the small spanner wrench provided for that

purpose, and bring the spindle in contact with the anvil. Hold the spindle

firmly with one hand and rotate the thimble to zero with the other. After

zero relation has been established, rotate the spindle counterclockwise to

open the micrometer, then tighten the thimble cap.

After tightening the

cap, check the zero setting again to be sure that the thimble-spindle

relation was not disturbed while the cap was being tightened.

(b) To adjust the rotable-sleeve type, unlock the barrel sleeve

with the small spanner wrench