Machining Fundamentals
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• A lock nut is used when several identical
parts are to be gaged. Refer again to Figure
4-11. The nut locks the spindle into place.
Gaging parts with a micrometer locked at the
proper setting is an easy way to determine
whether the pieces are sized correctly.
4.2.7 Reading an Inside Micrometer
To get a correct reading with an inside microm-
eter, it is important that the tool be held square
across the diameter of the work. It must be posi-
tioned so that it will measure across the diameter on
the exact center, Figure 4-17.
reverse order of the graduations on an outside
micrometer. See Figure 4-18. The graduations under
the thimble must be read, rather than those that are
exposed.
Figure 4-17. Using an inside micrometer. Extension rods can be
added to increase the tool’s measuring range.
Measurement is made by holding one end of the
tool in place and then “feeling” for the maximum
possible setting by moving the other end from left to
right, and then in and out of the opening. The mea-
surement is made when no left or right movement is
felt, and a slight drag is noticeable on the in-and-out
swing. It may be necessary to take several readings
and average them.
4.2.8 Reading a Micrometer Depth Gage
Be sure to read a micrometer depth gage cor-
rectly. The graduations on this measuring tool are in
Figure 4-18. A micrometer depth gage. When making mea-
surements with a depth gage, remember that the graduations
are in reverse order. This gage indicates a depth of 0.250.
4.2.9 Care of a Micrometer
Micrometers are precision instruments and
must be handled with care. The following tech-
niques are recommended:
• Place the micrometer on the work carefully so
the faces of the anvil and spindle will not be
damaged. The same applies when removing
the tool after a measurement has been made.
• Keep the micrometer clean. Wipe it with a
slightly oiled cloth to prevent rust and tar-
nish. A drop of light oil on the screw thread
will keep the tool operating smoothly.
• Avoid “springing” a micrometer by applying
too much pressure when you are making a
measurement.
• Clean the anvil and spindle faces before use.
This can be done with a soft cloth or by lightly
closing the jaws on a clean piece of paper and
drawing the paper out.
• Check for accuracy by closing the spindle
gently on the anvil and note whether the zero
line on the thimble coincides with the zero on
the sleeve. If they are not aligned, follow the
manufacturer’s recommended adjustments.
• Avoid placing a micrometer where it may fall
on the floor or have other tools placed on it.
• If the micrometer must be opened or closed a
considerable distance, do not “twirl” the
frame; gently roll the thimble with your palm.
See Figure 4-19.
• Never attempt to make a micrometer reading
until a machine has come to a complete stop.
• Clean and oil the tool if it is to be stored for
some time. If possible, place the micrometer
in a small box for protection.