PRECISION MEASURING AND GAGING - OD1642 - LESSON 1/TASK 2
inches, in steps of 1 inch; or in sets graduated to read in units of the
metric system, from 0 to 25 millimeters by hundredths of a millimeter.
However, in most shops, standard sets up to 24 inches are more common. The
larger sizes normally come as a set with interchangeable anvils which
provide a range of several inches. The anvils have an adjusting nut and a
locking nut to permit setting the micrometer with a micrometer standard.
Regardless of the degree of accuracy designed into the micrometer, the skill
applied by each individual is the primary factor in determining the accuracy
and reliability of measurements.
Training and practice will result in
proficiency when using this tool.
(2) The types of micrometer commonly used are made so that the
longest movement possible between the anvil and the spindle is 1 inch. This
movement is called the "range". The frames of the micrometer, however, are
available in a wide variety of sizes, from 1 inch up to as large as 24
inches. The range of a 1 inch micrometer is from 0 to 1 inch. In other
words, it can be used to measure work where the part to be measured is 1
inch or less. A 2 inch micrometer will only measure work between 1 and 2
inches thick. A 6 inch micrometer has a range of from 5 to 6 inches, and
will only measure work between 5 and 6 inches thick.
It is necessary,
therefore, that the machinist first find the approximate size of the work to
the nearest inch, and then select a micrometer that will fit it.
For
example, to find the exact diameter of a piece of round stock use a rule
and-first find the approximate diameter of that stock. If it is found to be
approximately 3 1/4 inches, a micrometer with a 3 to 4 inch range would be
required to measure the exact diameter. Similarly, with the inside and the
depth micrometers, rods of suitable lengths must be fitted into the tool to
get the approximate dimension within an inch, after which the exact
measurement is read by turning the thimble.
The size of a micrometer
indicates the size of the largest work it will measure.
(3) On some outside micrometers, the
frame can be smaller, so that
the range of the micrometer is only 0 to 1/2
inch or 0 to 13 millimeters; or
it can be larger, so that the range is 23
to 24 inches.
The head has a
constant range of 0 to 1 inch. The shape of
the frame may be varied to
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