roughness. It uses the tracer method and actually
measures the differences in the depth of the surface
The two main units of the profilometer are the
tracer and the amplimeter. Tracers are made in
several designs to measure a variety of shapes. The
tracer has a stylus with a very small radius at its tip.
As the tracer is moved across the surface being
measured, the stylus follows the contours of the
irregularities left by the machining operation. The up
and down movements of the tracer stylus are
converted into a small fluctuating voltage. The
voltage is fed into the amplimeter where it is
amplified to actuate the microinches meter on the
variations in the average roughness height in
Figure 2-7.--Master roughness scales.
provides mechanical movement of the tracer and its
stylus when manual operation is not practical.
You don't need technical knowledge or special
Move a fingernail along the surface of the job and
skill to operate instruments that are used to check for
make a mental note of the amount of resistance and
surface roughness. You can set up the instrument on a
the depth of irregularities. Then, move your
bench or cabinet beside the production machine and
fingernail across a series of master roughness scales
t h a t have numbers corresponding to their
finish must compare satisfactorily with the correct
This inspection requires you to use a microscope
with an optical flat plate and a monochromatic light
height of the surface irregularity in light reflected
between the microscope objective and surface of the
intersection of the wave fronts reflected between the
work and the front surface of the microscope
objective. The distance between the fringes
represents 11 microinches (11 millionths of an inch).
laboratories, but you should be aware of it in case you
encounter it during your career.
The profilometer (fig. 2-9) is the instrument most
Figure 2-8.--The interference (surface-finish) microscope.
commonly used to find the degree of surface