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Cydrome Leader

wrote:
On Fri, 4 Oct 2013 16:46:34 +0000 (UTC), Cydrome Leader
wrote:

Any wisdom here to share when it comes to hand tapping with roll taps?

I ordered some 1/4-20 and 10-32 ones to play with. I was having problems
with threads being stripped out of an aluminum pipe with a 1/4-20 bolt
with a knob that's used to clamp onto an inner cylinder.

Are a couple drops of cutting oil suitable as lubricant?

It seems some of these taps have flutes, some don't. Does it matter much?
You can use cutting oil for aluminum if tapping aluminum. The taps
that don't have flutes are not ground round. They are ground to have
high spots. If you grast the tap lightly and turn it you can feel the
eccentricity. A good hardware store will sell tapping fluid. The clear
works well for aluminum. For steel the dark sulfurized stuff is good.
You do know that hole size is critical for form taps? The hole will of
course be larger than for a cutting tap, but the size has less
tolerance than that for a cutting tap because the material is
displaced rather than cut.
Eric

I looked at some of the charts and other forums and the mention of using
larger and more specific hole sizes was mentioned.

Is it insanely hard to drive these things into metal, considering they
don't actually cut but form the threads with pressure?

I can't imagine their easier to drive than completely crossthreading a
fastener.