On Mar 14, 3:55*pm, Tim Wescott wrote:
On Wed, 14 Mar 2012 15:05:27 -0500, Jon Elson wrote:
Spehro Pefhany wrote:

Looking at using some relatively small screws tapped into (probably)
6061 aluminum. 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)?
I tapped quite a bit of 2-56 in 6061 using Alum-Tap fluid on a CNC with
rigid tapping. *I used some $8 spiral-point taps to push the chips
ahead. *The CNC guaranteed alignment straight over the hole.

There is a limit to how deep the hole can be for any particular tap
size, or the chips start to pack up and that's when you break the taps.
The tap manufacturer should have data on that.

The smaller the tap, the more critical the alignment parallel to the
hole becomes.

SmallParts used to (maybe still does) sell some magic wax that you put
down a blind hole, then tapped. *The idea was that as you tapped the wax
would be deformed and push up the tap flutes, taking the chips with it.

Cool (and expensive) as all get out. *I have no idea how well it works,
or if it's available in #0.

I think I remember that stuff, was formed "wires", IIRC. I've used
the regular Castrol machining wax to do the same, just stuff a lump in
the drilled hole. Got it for the bandsaw, works for that as well.
Aluminum really needs that, you don't want chips welding onto the tap
with that small a thread. Have even seen a very old tip using bacon
grease for that back in the "olden days"('20s).

And I wouldn't be doing anything that small without some sort of tap
guide, I use a very small Starrett dogbone wrench for those dinky
taps.

Stan