[rowbare]

I do a lot of M2.5 threaded hole, and each of them has to be hand tapped. M2.5 with a compression holder is, I'm told, "not advised."
With rigid tapping, you have the hardware drive down Z exactly in line with the speed of the spindle. If you have an encoder on the spindle, this is technically simple.
However, more interesting, is the use of BLDC motors in the current lower-end mills. Because of the way BLDC works, the controller knows at all times where the motor is (within a few degrees) because it needs this knowledge to properly drive the motor phases. Thus, this knowledge that it already has, could be extracted and used, using basically software only.
Now, would this be the first time a company has considered charging for a purely software upgrade? No.
(I hear Haas charges thousands both for the ability to use all the RAM that's already in the controller, for actual G-code programs, and for turning on the bit of the software that looks more than one move ahead to plan the toolpath. I would, too, if I were like them, and could get away with it!)

Get an auto-reversing tapping head for the small taps. Don Clements has been using a Procunier for years with great success.

bob