Schmidt 300 and 600 grit tone hole finishing files are extremely flat, with
diamonds embedded into the metal surface. They are designed for applying
finishing touches to the tone holes. Screw on a plastic disk to the
abrasive side of the larger metal disk in order to locate the rotary
tone hole file in a hole.
Use the ball end driver to turn the tone hole file. The ball driver allows
the file to tilt a little to find the correct level. Be sure to use a
drop of light oil to help keep the abrasive from clogging. Use light
pressure when finishing up or you will flex the tone hole and it will
not come out flat. Mark the tone hole rim with a black felt pen
(Sharpie) so you know when to stop as the low spots disappear.
Be sure to dress up the inside & outside diameters of the tone hole
rim with chamfering tools to take off any sharp edges or burrs that
would cut into the pad and to restore the crown of the hole.
After cutting the tone holes, check their flatness with the bare metal side
of the tone hole file (use a leak light). If a file loads up with metal,
use an ultrasonic cleaner. You can also use a needle (or wire brush),
but you should do so while viewing with powerful magnification such as a
microscope or strong Optivisor.