Roll tap variations...

Awl --
Have you noticed that some roll taps seem perfectly circular, almost like a screw, while others almost resemble cut taps, but with much smaller gaps --
but with a bit of a "cut edge". Just got some Nachi 1/4-20s, and after I drilled the #1 tap hole, I looked at the tap and groaned, Ferchrissakes, this is a CUT tap.... but it's not, apparently. Let's hope not, cuz it's hard to turn a #1 hole into a #7 hole..... :( Kinda weird... I'm wondering if some of these taps aren't a kind of hybrid or sumpn....
Haven't used the nachi yet, as it's nappy-poo time....
--
EA



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http://www.komet.com/tools-navigation/tools/threading/roll-form-taps.html
Different style roll/form taps for various applications, materials & coolant process. Some roll/form taps may look similar to cut taps but that is where the similarity ends.
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That there slot in that tap is a pressure/coolant/oil release passage, it does no cutting, it is merely a place for the pressure to go to, prevents hydraulic compression. It is on most all roll taps over 1/4
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wrote:

That there slot in that tap is a pressure/coolant/oil release passage, it does no cutting, it is merely a place for the pressure to go to, prevents hydraulic compression. It is on most all roll taps over 1/4 =======================================OK, that sort of explains the roll taps I have that are kind of flatter on a couple of sides -- those may be relief-type reduced radius, instead of a formal slot.
It also mebbe explains why those perfectly round roll taps I got *suck*. Sheeit, you could proly just harden a screw, and get the same effect, eh?
The slot in the Nachi's seems sharp enough to cut, but apparently it doesn't, as I used them successfully in pretty deep 1/4 tapped holes, about 1.1" . Did a great job, indeed no chips. $15 each, which for me is a nail-biting fortune.
Mebbe what those slots also do is kind of start the rolling/forming process, kind of like the tip of a plow?
--
EA



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    I think that the grooves are for blind holes when you need to provide a path for the lube to exit as the tap is going in. A through hole doesn't need the lobes, so it is more likely to get a smooth tap.

         Nope -- just lube clearance. Say you stick it in Castrol wax before running it into the hole. With a smooth one and a blind hole -- especially if there is any liquid lube already in the hole, you will be generating rather serious hydraulic pressures.

    O.K. Good Luck,         DoN.
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