USE/CARE OF HANDTOOLS & MEASURING TOOLS - OD1621 - LESSON 3/TASK 1
(b) The steel spindle is actually the unthreaded part of the
screw.
It is the spindle that advances or retracts to open or close the
open side of the U-frame.
The spindle bearing is a plain bearing and is
part of the frame.
(c) The hollow barrel extends from this bearing; on the side of
the barrel is the micrometer scale, which is graduated in tenths of an inch,
and which is, in turn, divided into subdivisions of 0.025 inch. The end of
the barrel supports the nut which engages the screw. This nut is slotted,
and its outer surface has a taper thread and a nut which makes it possible
to adjust the diameter of the slotted nut, within limits, to compensate for
wear.
(d) The thimble is attached to the screw, and is a sleeve that
fits over the barrel. The front edge of the thimble carries a scale broken
down into 25 parts. This scale indicates parts of a revolution, while the
scale on the barrel shows the number of revolutions.
The thimble is
connected to the screw through a sleeve that permits it to be slipped in
relation to the screw for the purpose of adjustment. The inner sleeve is
sweated to the screw. The outer sleeve is clamped to the inner one by the
thimble cap.
Loosening the cap allows it to slip one in relation to the
other.
(e) On top of the thimble cap there may be a ratchet. This device
consists of an overriding clutch held together by a spring in such a way
that when the spindle is brought up against the work, the clutch will slip
when the correct measuring pressure is reached. The purpose of the ratchet
is to eliminate any difference in personal touch and so reduce the
possibility of error due to a difference in measuring pressure.
Not all
micrometers have ratchets.
(f) The clamp ring or locknut is located in the center of the
spindle bearing on those micrometers equipped with it. This clamping makes
it possible to lock the spindle in any position to preserve a setting.
d. Use of Micrometers.
(1) Reading Standard Micrometer.
Reading a standard micrometer is
only a matter of reading the micrometer scale or counting the revolutions of
the
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