PRECISION MEASURING AND GAGING - OD1642 - LESSON 1/TASK 2
not reset the measuring surfaces to close contact because the projecting
film of oil will be squeezed out.
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
(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