I never did many blind holes where the threads were required to go all the way down....usually there was enough clearance that I could set a stop for the drill press quill and the tapping head quill would feed until it hit neutral and you could bring it back up. The few that required threads all the way, I would carefully adjust the tapping head clutch so you could bottom a gun tap without breaking it, and then finish the threads with a bottoming tap by hand*. Making my own products, I had the luxury of designing out such handwork usually.
Still, I'm thinking in terms of 10-32 and up sizes...I rarely went below no. 8. It would indeed be a bit more worrisome on no. 4 and no. 6 sizes, esp. in aluminum .5 thick. No. 0 Bilz type tap holders with clutch, would probably be more sensitive to clutch adjustments than a standard Tapmatic head, so might be preferable in that case. Tap lube will be critical also...I'd recommend Acu-lube but there are others.
The ultimate tapper for the smaller sizes is of course made in Germany...called MicroTap. About the size of one of those tiny Servo drill presses, it has electronically programmable torque settings and some other neat features. Suspect it's a bit beyond the home shop budget however...I seem to recall a price tag over $5,000.
www.microtap.de
*Btw, even when tapping by hand, if 1/4 inch or smaller, I don't like having to trust my "hand" to not get "over enthuseastic"...so, even then I often use an overload clutch. I made a T bar that will hold a standard Bilz clutch tap holder and use that. In the no. 8 and 10 sizes I can sometimes just grip the Bilz holder itself without even using the T bar.
[This message has been edited by D. Thomas (edited 03-10-2002).]