Re: General Tool Life Question

GM4T:

I too am a "home shop machinist" and time is not that important. I also
haven't tapped as many holes as most here. But your 1 degree advance before
chip breaking seems too conservative. I usually put on a quarter to half a
turn then break the chips. I missed the start of this thread, is it steel you
are tapping into?

As someone else did, I'd strongly recomment tappered taps. Usually you can
drill holes beyond the depth of thread needed and not bottom tap. This
requires only the tapered tap. If bottoming is needed I tap with a tapered
tap and finish with a bottoming tap. I've never had to use a third,
intermediate tap.

I have been told, but do not do this, that many drill the hole for tapping
oversized. Unless you are pushing the thread strength capacity it does not
matter that you do not have full threads. If you aren't engineering the joint
and using a torque wrench or similar in tightening the screw/bolt you aren't
using the full capacity.

Finally, if you are on this list and interested in machining, you will be
tapping holes in the future. These taps will not be for just a one time
project. :-)

Hope this is of use, and not incorrect. :-)

On Wednesday 16 January 2002 09:57 am, you wrote:
> I actually am using one tap for each hole size. I wouldn't want to
> buy too many taps because this is a one-time project and I wouldn't
> need them anywhere else. When I tap the holes I do it very slowly and
> very little at a time using a plug type tap. I turn a very small
> amount, maybe like 1 degree or more before backing it out. Which is
> why it takes so long for me to tap one hole. But time isn't a
> priority for me. It took more than an hour to tap a 1/4-20 thread for
> 3/4". I use a lot of cutting fluid on it and the chips drip off in a
> clump.

--
Hugh Currin, PE
Mechanical Engineering Technology
Oregon Institute of Technology