Roll Taps (Flute-less Taps)

[Tungsten dipper]

What are they used for? Any background or information would be appreciated.

[Dan Dubeau]

Also known as thread forming taps. They actually "form" the thread instead of cutting it. Stronger threads, and stronger taps that last much longer in production machinery than traditional cut taps. I've been using the same 1/4"-20 form tap in our haas' at work for about 5-7 years now (can't remember when I changed it), and the number of holes it's tapped has got to be in the 5 figure range. They can be picky about starting hole diameter, so be careful of that. They need a bit bigger hole to start with than a cut tap. For the 1/4"-20 I use a #1. There is information out there, but it's not usually contained on the normal machinist thread charts in circulation.

Here's the first google search I did. https://kar.ca/pdf/REFERENCE_TapDril...ps_oct1217.pdf

[projectnut]

Thanks for the link to the thread forming tap chart. I've been using them for several years and have to go through the math each time I use a different size. I try to keep a record of the sizes needed, but haven't done as good a job as I should. I've researched for hours at a time trying to find a wall chart or something that could be printed into one. All I seem to come up with is the standard thread cutting tap charts regardless of the search terms I use.

I'll be taking either a printed or electronic copy of this chart to a local shop to get a couple copies printed. Thanks again.

[Doozer]

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

[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?

[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!

[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......

[old mart]

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

[Doozer]

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

-D

[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.

[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

[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.

[Tungsten dipper]

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

[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.

[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