Thanks for all the help everybody, I appreciate the effort. The holes
themselves are drilled on a press. I do that with a jig I built that
has quick release clamps that just locks the round in. I can't use the
press to do the tapping because I don't have the reverse head. But if
I did, I would just go with the combo drill/tap, because it would be
silly not to, and it would be too hard to re-align the hole for the
tap once you take it out of the clamp. I've been doing the counter
sink by just pressing each one against a counter sink for a few secs.

But yes, believe it or not, up until now I had been doing 500 or more
on one tap by just putting the piece in a vise and using a power
drill. I put a dab of lube in the hole and it seemed to work fine. I
was using the same aluminum from the same dealer, same alloy as far as
I can tell, and the taps look to be exactly the same as the past ones.
So I don't know what started going wrong.

But I will probably get the tap head and that will save a lot of time
in the end. I notice HF has one, but it doesn't appear to have the
safety clutch.