Useful Tips of Using the Micrometer Caliper
We can use a micrometer caliper to measure the size of objects with
a precision of one hundredth of a millimetre.The object to be
measured should be placed between the jaws of the micrometer and the
jaws are carefully closed on the object by rotating the thimble.The
distance between the jaws and the size of the object is read on the
barrel of the micrometer. A micrometer caliper works on the
principal of a screw. If a screw is turned by one revolution, it
advances by a distance equal to the pitch of the screw. Then a
fraction of a rotation advances it by a corresponding fraction of
the pitch. It is common that a micrometer caliper to have a screw
with a pitch of 0.5 mm per revolution, and a thimble calibrated in
fiftieths of a revolution.One fiftieth of a revolution is equal to
0.01 mm travel of the screw, so the readings on the thimble give the
distance that the screw has moved to the nearest 0.01 mm.
Calibration marks on the sleeve of the micrometer give readings of
how far the jaws are open to the nearest 0.5 mm.The reading on the
sleeve is added to the reading on the thimble to give the total
distance between the jaws of the micrometer. Micrometer calipers
often do not read zero when the jaws are closed.To correct for this,
a“zero reading”must always be taken. This zero reading is then
either added to or subtracted from the reading obtained for the
object. If the zero reading is below the reference mark, it is added
to the reading; if it is above the reference mark, it is subtracted
from the reading.
It is extremely important for us to close the micrometer caliper
gently any where at any time because the screw has a very high
mechanical advantage and a large tension can easily be put on the
jaws if one is not careful. Use the ratchet on the end of the
thimble if there is one.This will automatically put the correct
tension on the jaws.When you are finished using a micrometer
caliper, always put it away with the jaws slightly open to allow for
any thermal expansion.