I have used the diamond flywheels with a high speed hand piece at
high RPMS- the trick seems to make practice cuts first to determine
the angle that provides you the best looking cut and then be
consistent with repeating the angle which you bring the work piece to
the wheels. The key is to let the diamond do the work, do not press
hard into it or
1) the mandrel will bend
2) you will dislodge the diamond
3) you will chip the diamond or any of the 3 combined. Also when you
chuck up the flywheel do not leave a lot of the mandrel out past the
collets of the hand piece other wise it is prone to easy bending and
will become off center.
I would recommend having the hand piece mounted and bring the work
to the wheel. I suspect that your person is trying to bring the
flywheel to the work piece instead which would not be as controllable
in terms of angle and feed rate.
Also, when you buy flywheels they are available in different angles
of cut- you have to experiment with which one works best on the
application you are doing.
Be sure and wear eye protection as the swarf can hurt you -