The Dark areas are
as result of
normal use. Note the wear areas are on
both sides of the plate. This
is good and indicates that the Inspector
is using different areas
to prevent major wear
in one area. These
areas are only a few
tenth's, ( .0001's ), however if all of this wear was
to occur in one place, it would be
thousandths, ( .001's) of an inch.
After lapping, all of the plates
using a repeat-o-meter.
an indicator on a height stand but uses a
indicator to determine the ability to
duplicate a reading
anywhere on this
surface. This is only one half
of the calibration
due to the fact that a repeat-o-meter can not determine
Autocollimator is used to measure the flatness of the surface plate.
This instrument uses collimated
light that is bounced
off of a mirror mounted
on a sled selected
for its pad spacing. Sleds work like sine bars and
into millionths of an inch, rise or fall when moved in
equal to the pad
spacing. This data is assembled
into an actual contour plot of
the surface plate and
This information is
used to produce a Certificate of Calibration
that is traceable to NIST
and compliant to ISO/IEC 17025-2005,
Mil.Std.45662, ANSI/NCSL Z 540-1 & TS 16949.
This Cert. references the
tolerances in the Federal Spec. GGG-P-463c
The "actual flatness"
Validates compliance to these
This Cert is a real tool
that gives you relevant
information that allows
you to use your
surface plate to its full potential.