USE/CARE OF HANDTOOLS & MEASURING TOOLS - OD1621 - LESSON 3/TASK 1
not necessary, since there is no fractional part of a space to determine.
The reading is 2.350. The 0 mark on the Vernier scale, as shown in figure
188, view B, on the previous page, coincides with a fractional part of a
space on the rule. The reading is 2.35 plus a fraction of the space on the
rule. In order to determine what fractional part of a whole rule division,
or how many thousands are to be added to the 2.35 reading, it is necessary
to find the line on the Vernier scale that exactly coincides with the line
on the rule.
In this case, the line coincides at the 18th mark.
This
indicates 18/25 of a whole space. Since each space on the rule equals 0.025
inch, this part of a space is equal to 0.018 inch, and the total reading is
2.34 plus 0.018, or 2.368 inches.
NOTE
Vernier scales are not necessarily 25 divisions long;
they may have any number of units. For example, the
ten thousandths micrometer has a Vernier scale of only
ten divisions.
(b) Applications. The Vernier caliper has a wide range of measurement
applications, and the shape of the measuring jaws and their position with
respect to the scale makes this tool more adaptable than a micrometer.
However, the Vernier caliper does not have the accuracy of a micrometer. In
any 1 inch of its length, a Vernier caliper should be accurate within 0.001
inch.
In any 12 inches, it should be accurate within 0.002 inch and
increase about 0.001 for every additional 12 inches.
The accuracy of
measurements made with a Vernier caliper is dependent on the user's ability
to feel the measurement. Because the jaws are long, and because there is
the possibility of some play in the adjustable jaw, especially if an
excessive measuring pressure is used, it is necessary to develop an ability
to handle the Vernier caliper. This touch may be acquired by measuring such
known standards as gage blocks and plug gages. Applications of the Vernier
caliper are shown in figure 189 on the following page.
In view A, a
machinist is checking the outside diameter of a part. One hand holds the
stationary jaw to locate it, while the other hand operates the adjusting nut
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