On 2012-03-14, Spehro Pefhany wrote:

Looking at using some relatively small screws tapped into (probably)
6061 aluminum.

6061-T6 or a softer version?

Through holes, maybe 0.08" of material. Is it insanity
to think about using a cordless hand drill and run them right through
without backing off (assuming a good quality coated tap and aluminum
cutting fluid)?

First off -- unless you include spiral point (or "gun tap") in
your description of "good quality coated tap" -- forget it. You need a
tap designed to chase the chips ahead of the tip, or a spiral flute tap
designed to chase the chips back out the starting side to go continuous
feed. Other taps need to be reversed every half turn or so to break the
chips or they will clog and break.

Second -- you need something which will hold the tap straight
(especially for something as fragile as an 0-80) (which, BTW, you only
mentioned in the "Subject: " header, and some newsreaders stop
displaying the "Subject: " header once you are into composing a reply).

The ideal thing is a smaller (say 30X) TapMatic tapping head,
which can be set to limit the torque so when a tap dulls it will stop
turning. And when you set it up, use the depth stop to stop the feed of
the assembly at a proper point. The tap will self-feed for another
couple of turns or so (maybe four with 80 TPI) and then disengage a dog
clutch so the motor keeps spinning but the tap stops. When you withdraw
the quill the tapping head will switch into reverse, and back the tap
out faster than it went in. It works fine in a drill press (once you
set up a stop for the reaction arm sticking out the side of the head).

eBay auction # 280843542733 has an example of the right size,
30X -- #0 through 1/4" taps. This one has a break in the collet closing
cone, and I would probably go for a different one, but this is an early
one with good photos. No clue as to what size arbor it has, but those
can be replaced.

To get a tap a little less fragile, look into "thread forming"
or "thread rolling" taps (which need a different size tap drill, BTW.
But in 0-80 size, I still doubt that you could hold the drill stable
enough to avoid breaking it. Especially considering that you need to
reverse the drill motor to back the chip out, and many have reverse
switches which are hard to switch without joggling the angle of the
drill motor and thus breaking the tap.

Good luck,
DoN.

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