Roll Taps (Flute-less Taps)

[DR]

not saying roll form taps can't be used in steel at all (though I think work hardening forms of stainless are a no no), just that I don't have the balls to try it yet

A little secret...there are easy machining stainless alloys. 316 Carpenter Project 70 was one we used a lot. Amazingly easy to machine. Unfortunately Carpenter has gotten hard to buy small quantities from of late. Other stainless mills produce their own versions.

What they do is skew the elements that make machining difficult to the low side of the alloy spec. The elements that help machineability are skewed to the high side. And the material is fully annealed . Cost is two to three times regular material, but worth it in the savings on tooling.

[mochinist]

not saying roll form taps can't be used in steel at all (though I think work hardening forms of stainless are a no no), just that I don't have the balls to try it yet

We use them down to 2-56 and m2x.04, in aluminum, steel, and stainless 303/304/316, almost daily in a job shop environment. For the smaller sizes we tend to drill and ream

[johansen]

When i get around to it, im going to try and make a thread forming tap from a grade 8 bolt that has been squished between 3 complient surfaces such as mild steel, to press the bolt into a triangular profile, then harden the bolt.

the pitch diameter might be high but most bolts are on the low side of things to start with.

[epicfail48]

Form taps are awesome, especially in smaller sized. Making butterfly knives a while back, i needed to put a 2-56 thread 7/16" through o1, trying to do that with a cut tap resulted in a broken tap about 60% of the time no matter what i did. Form tap with the proper drill went through like butter, under power no less, without any broken taps. The lack of flutes makes the taps way stronger

[mattthemuppet]

not saying roll form taps can't be used in steel at all (though I think work hardening forms of stainless are a no no), just that I don't have the balls to try it yet

[DR]

One of my long repeat jobs required a 10-32 blind hole tapped 7/8" deep. There's no practical way to do smallish diameter blind deep holes except with form taps.

Another cool use is threading holes in sheet metal. Make the tap drill hole way small so the tap forces the material to extrude out the back side, You can get lengths of thread engagement three to four times the thickness of the sheet metal.

Not all thread forming taps are created equal. The first ones we tried had a groove up the side to relieve hydraulic pressure from the tapping fluid in the hole. Those proved to not be so good because the groove would get clogged with swarf and break the tap. The best had a four lobed cross section with plenty of relief for the trapped cutting fluid.

Forming taps get dull. They wear down in the first few threads from the end. It isn't readily visible to the eye. The way you find out is your deep hole has a tapered thread in the bottom. You can't restore the worn tap to original, but you can cut the worn end off and easily grind a new starting chamfer on the end.

[Tungsten dipper]

Thanks everyone! This is great! Dan, thanks for the chart too!

[Toolguy]

It still does that when the tap drill size is correct. It would take too much force to make the thread crests into a nice pointy or flat top shape like a cut tap.

[Rich Carlstedt]

The threads made by roll-form taps roll a burr and make a thread that is easy to cross thread when being assembled.
I never allow roll-form taps on any prints that I generate. Just leads to assembly troubles.-Doozer

I suspect that may occur when the tap drill size is too large ?
Rich

[Mark Rand]

they're great for use in alu, especially when there are fewer threads engaged than is ideal. They can be used in steel, but I don't think I've ever had the guts to do so!

I used one 4mm form tap to produce 160 threads in blind holes in O1 drill rod and it was still good at the end of that little job. Using a tapping head and the drill press made it very fast.

[Doozer]

And they hoop stress the heII out of a part
so no thin wall bosses or they will split.

-D

[old mart]

They are very sensitive to the starting hole diameter and the ductility of the metal. Not for general use.

[Dan Dubeau]

they're great for use in alu, especially when there are fewer threads engaged than is ideal. They can be used in steel, but I don't think I've ever had the guts to do so!

One of the kids here tapped a bunch of holes in 4140 with the 1/4-20 just fine before I told him to only use that tap on aluminum lol. Doozer is right, they DO leave a sort of "double track" that lends itself to cross thread on initial assembly if you're not careful. We have one guy here that HATES them and always complains about them, but then again there's not much he doesn't complain about so......

[mattthemuppet]

they're great for use in alu, especially when there are fewer threads engaged than is ideal. They can be used in steel, but I don't think I've ever had the guts to do so!

[rklopp]

Maritool’s plastic data cards that he used to pack with shipments had both cut and form tap drill sizes. Maybe he still offers those?