In article ,
Jon Danniken wrote:
"Jeff Wisnia" wrote:

[ ... ]

Can you honestly say you've never broken a tap? Isn't that how we all
learned how to avoid busting them?

Hehe, I just broke one last week, a 6-32. I have 16 little holes to tap
radially in some short lenghts of 3/8" all thread (for set screws), and
since it takes a longer time to do the "twist-in, twist-out", I decided that
I would do it like the tapping machines do it, and do it in one fell swoop.
This way I would save a lot of time.

Of course, I don't have a tapping machine, and at the time I didn't even
have a proper handle (I was using an old set of Vise-Grips).

And -- more important, you probably did not have a "gun" tap --
a spiral point tap designed for the tapping machines. They are designed
to chase the chips ahead of the tap. Normal taps (starting, plug, and
bottoming) generate the chips in the flutes, and need to be backed up to
break those chips free before they get big enough to totally wedge
things.

Guess what - I broke a tap!

And -- the 6-32 is probably the easiest tap to break. It is
weaker than any other common tap, because the threads are deeper
relative to the OD of the thread. I would much rather tap 2-56 or even
0-80 by hand than 6-32.

I bought a proper handle and I'm doing all of my hand tapping now with the
"twist-in, twist-out" technique. At least now I know why.

Get some "gun" taps, and use a proper tapping lube and you'll do
a lot better without the periodic backup. But make sure that there is
enough clearance on the other side for the chips to fall out. If you
are dealing with a blind hole, I would suggest either a spiral flute
tap, or even better (though more sensitive as to the size pilot hole)
thread forming taps, which don't generate chips at all.

Good Luck,
DoN.

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