PRECISION MEASURING AND GAGING - OD1642 - LESSON 1/TASK 2
Read the highest line on
the vernier scale (3) which
lines up with a line on
the scale (7) and record ..............
(3) Use and Application.
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
However, the vernier caliper does not have the accuracy of a
In any 1 inch of its length, a vernier caliper should be
accurate within 0.001 of an inch. In any 12 inches, it should be accurate
within 0.002 of an inch. Inaccuracy increases about 0.001 of an inch 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 there is the possibility of play in the
adjustable jaw, especially if an excessive measuring pressure is used, it is
necessary that one develop an ability to handle the vernier caliper. This
touch may be acquired by measuring such known standards as gage blocks and
There are various applications of the vernier caliper.
figure 47, view A, on the following page, the machinist is checking the
outside diameter of a part.
One hand is holding the stationary jaw to
locate it, while the other hand operates the adjusting nut and moves the
sliding jaw to the workpiece.
The same procedure is used in view B in
checking the inside dimension.
(a) The accuracy of the vernier caliper depends on the condition
of fit of the sliding jaw, and on the wear and distortion in the measuring
surfaces. The fit of the sliding jaw should be such that it can be moved
easily and still not have any play. It may be adjusted by removing the gib
in the sliding jaw assembly and bending it. The function of the gib is to
hold the adjusting jaw against the inside surface of the blade with just the
right amount of pressure to give it the proper friction.
(b) Wear on the jaws of the vernier caliper is mostly at the tips
where most of the measurements