Re: Speed of Tapping Head? - tap styles

--- In CAD_CAM_EDM_DRO@y..., "turbulatordude" <davemucha@j...> wrote:

> <snip>
> Spiral flute are much weaker and are typicaly used
> on softer materials like Aluminum. but for aluminum
> I use self forming taps.

> Makes a better hole, burnishes the inside so the threads
> are not as soft, and does not leave any chips. And they
> are available in bottom tap, so you can tap deeper on a
> hole without pulling out to remove chips.

I've been thinking about trying thread-forming taps.
I read somewhere that you have to use larger tap drills
with forming taps to make up for the fact that the tap
doesn't remove any metal. How do I select the right tap
drill size - info for thread-forming taps isn't in
Machinery's Handbook or any of the other books I have.

John Kasunich