Re: Rigid tapping: how is it done

When rigid tapping, the spindle location in terms of rotation is accurately
followed by the CNC control. In step with this, the Z axis is commanded to
move as a slave to the spindle with the programmed thread lead as the
multiplier. The machine must have a very accurate lead screw and fast servo
response as any relative movement between the actual and ideal location will
result in "stretched" threads. Worst case, you could have a broken tap. A
spindle encoder would be needed in addition to the z axis encoder/motor
assembly. I've never seen this done with stepper based equipment but I guess
it could be done. There are stepper based lathes that single point thread.
This is very close to rigid tapping except that the spindle must stop and
reverse. You could get close to rigid tapping with a floating head or fake it
completely with a tapping head.
Peter