A majority of all service calls eventually
point to the customers real problem, dull
plates. Next to plate sharpness, plate
flatness is important. Grinder plates should
be ground flat, or slightly concave. Using a
precision straight edge and feeler gauges the
amount of concave can be determined (see
page 15). Plates that are ground convex will
not work properly. The knife inserts will
not seat at the outer edges of the plate, and
the product will not be cut cleanly.
The plates also must be uniform in
thickness. If the bearings in the table of
your surface grinder are worn, it is possible
that the plates will not be uniform. Using a
micrometer, measure around the outside
edge of the plate, there should be less than
.0005 variation. Measure around the inside
diameter also, this should also show less than
.0005 variation. If the measurements are
consistently less at the inside diameter than
at the outside diameter you also may assume
that the plate is concave, and if thicker it
may be convex. It is rare that a plate would
be convex on one side and concave on the
other, but measuring with a ground straight
edge and feeler guages is the best test for
flatness.
20
If your plates are turning blue, the operators
are running the grinder empty. The blue
color indicates temperatures up to 600°! This
is above the draw temperature of this steel,
and unless the heat affected zone is removed
this plate will crack. Under careful
examination you may be able to determine
how deep the discoloration is by looking
down the holes. We recommend removing
this layer, plus .030! Plates with cracking
between the holes can be attributed to this
condition 99% of the time.
The most important feature, however, is
sharpness. Most people think that a grinder
plate should shine like a mirror, the fact is
that a certain amount of roughness is
required. The roughness of the plate is what
keeps the the inserts sharp. We supply a
specially manufactured grinding wheel that is
36 grit, rather than the 60 or 80 that other
companies sell. The grains themselves should
be soft and what is called friable, that is when
dull, it should leave the wheel. If you buy a
good knife, you sharpen it with a very soft
stone. These plates are harder and tougher
than a knife blade, therefore it only makes
sense to sharpen it with a soft stone. Dress
the wheel before sharpening each plate. Do
not let the wheel spark out, when the plate is
sharp, get the wheel off the plate!
