Sharp SH-920 Instruction Manual page 51

Clamp the magnetic chuck to the machine table.
3.
3.1 Rough grinding the chuck surface same as the grinding of the underside of
the chuck, but with different clamping method.
3.2 Switch on the magnetic chuck and then fine grinding the surface with
0.005mm wheel infeed.
3.3 Spark out grinding with no infeed, 2 to 3 times passes of wheel over the
chuck surface.
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