Servo as a Spindle - Mariss?

I want to use a DC brush servo as a spindle motor to give co-
ordinated motion for tapping, but also have the motor run
continuously fwd/rev. when machining as a regular spindle motor.

I'm thinking it would be fairly easy to have a circuit that
would "engage" the G320 servo drive for tapping and then switch over
to direct DC or a PWM to act as a regular spindle motor. Aside from
the ERR/Reset pause when "engaging" the servo drive, any problems
with doing this?

Brother tapping machines use a large servo as the spindle motor and I
think they do something similar to what I described.

Does anyone have any suggestions. This topic may have been covered
before. Also, the availability of higher speed servos like 5000 rpm
or more, in the size range .1 to .25 KW?

Thanks, Joe V.