Re: Rigid Tapping--How is this accomplished?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Kim Lux <lux@d...> wrote:

> The thing I don't understand about this setup is how the
> tap can totally cut the thread without breaking. For
> example, if I am cutting a thread by hand, I must
> advance/reverse the tap 25 times to reach the bottom of
> the hole without breaking the tap. How could a milling
> machine power the tap right to the bottom of the hole
> without reversing the tap ?
> Won't it break the tap ?

You just have to use the right taps <g>!

The traditional straight flute tap is known as a hand tap,
and you are right - you must reverse it frequently to clear
chips.

Machine tapping is done with either spiral point taps (aka
gun taps), or with spiral flute taps. Get out your favorite
tooling catalog and look at the pictures to see the difference.

Gun taps push the chip forward into the hole. They work very
well on thru holes, because the chip has someplace to go.

Spiral flute taps pull the chip back, like a twist drill.
They are much weaker than gun taps, and as the hole gets
deeper the chip will still tend to get stuck. But for shallow
blind holes they are the right choice.

IMHO buying hand taps is a waste of money - even for hand
work, I'd much rather use a gun tap.

Summary:

Gun tap (spiral point): best overall, but can't use on
shallow blind holes.

Spiral flute tap: good for blind holes

Hand tap: I'll take them if they're free and a size I don't
have...

YMMV

John Kasunich