Karl, thanks. I will try on some aluminum junk that I have, first.

Tapping, as Richard noted, may be a challenge.

What tap would you recommend for this (tapping aluminum)?

I don't agree with Richard's analysis. His method assumes the
probabilty of a broken tap is the same on every hole. In fact, once
you've set up proper conditions and selected a top quality tap the
probablity of breaking goes with wear. Taps used in machines last FAR
longer than hand taps.

I use OSG brand taps. Gun flute on thru hole, spiral flute on blind
hole. I forget, you aren't set up for rigid tapping??

Both your tension/compression tap holder and the procunier can be set
up in your CNC. But, its tricky. You've got to match feeds and speeds
to where the tap wants to be.

Karl