You should not exceed 5000 rpm going into a hammer handpiece. The mechanisms that translate spin into impact are delicate, and burn out at high speeds.
On an almost unrelated matter, does anyone know how an air driven
ultrasonic dental handpiece works? I assume it is virtually the same
as a hammer handpiece but working at around 20,000 b.p.m. I had
wondered whether the same system could be used with abrasive for
Ian W. Wright