Form tap geometry

Awl --
I've taken to form tapping aluminum (cnc rigid tapping mode), and have noticed a wide variety of geometries in these taps.
The name-brand form taps I have (Nachi, Emuge) almost look like cut or hand taps, as they have between 2 and 5 sharp-edged flutes. I have others which have no flutes whatsoever (they look almost like a screw!), and others with a slight recess instead of a true groove,, and one that looks almost oval.
Any insights into the preferred style of form tap? Does this style vary with context, metal, etc.?? Suggestions on best bang fer the form tap buck?
--
EA



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On Sunday, April 21, 2013 8:38:01 PM UTC+1, Existential Angst wrote:

We use the 5 point fluteless type. For small sizes double drill the hole, first .01" under recommended size and second with the recommended one, it helps with the core diameter.
Add .001-.002" to the recommended drill size if the core diameter is below top limit.
Never use them in a high value job, it will break one day and scrap the part. We are gradually replacing rolltaps with threadmills for new jobs.
DanP
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wrote:

I prefer Balix as it's what I've used the most frequently. I've had very good success with them. I have no comment on tap geometry. All I have ever been interested in is the end result and how long the tap will last:
http://www.balax.com/
=================================================Your balax taps seem to have 1 groove. My nachi 1/4-20 has two; emuge 1/4-20 has 4, the 5/16, 3/8 has 5. http://www.emuge.com/multitap/mt-form/selection.html Sheeit, I paid list for those muthafuckas..... ahma haveta to talk to haas about that.... LOL
My no-name 5/16 stuff has no groove at all, looks perfectly round, like a screw.
Don't know what it all means. One implication might be this:
With at least one groove, the tap can release air/coolant from a blind hole. One of my worries with the no-groove imports is that they might could trap/compress coolant in a blind hole, and, well, coolant is incompressible.... Don't know if that's a valid concern, but the thought did occur.
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EA




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wrote:

Since I'm still 'sperimenting w/ the gr510, which has all kinds of load indicators'n'shit, I'll tap with the emuge and the imports, see if I there is a detectable load difference, as well any diffs in the fit/appearance of the tapped hole itself.
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