Theoretically, you should use a reversing tap attachment on a drill press under power, but in this case, I was tapping a through hole in aluminum, and it was jig for holding something, so if I screwed it up, no big deal. I set the drill press at 200 rpm, made sure the tap was exactly centered over the hole, started it running, and then lowered into the hole and turned it off as soon as I was sure it had engaged. However: even then it still made quite a few more turns in than I needed, so I had to back it out by hand, and this took quite a while.
I'm not sure that it actually saved me anything time wise over hand turning the tap in the drill press. It was nice to know that it worked, however. Perhaps I will try this again with my finger on the power switch, and turn it off as soon as it contact metal. At 200 rpm, even one second is a bit more than three turns, and that's most of the way through the 1/8" wall aluminum that I am usually drilling and tapping.
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