Form tap or cut tap 1/2-13 in 12L14?

If it's not broke, don't fix it. I'd stay with the cut tap as you've already had success with that method.

Best, Steve

I've seen people grind away most of the back threads on a tap, so that only about 1/2" worth of threads do the cutting. Actually, proly only a few threads do the cutting, right?

Good idea? Bad idea?

I've noticed that OSG has gone to a similar idea on their taps, a small amount of threads and the rest is relieved down to just under the minor dia. If they're doing it on their standard lines I see no reason not to.

I like interrupted taps for pipe taps but a quick search didn't turn up those for the larger standard taps. I'm curious as to why?

Best, Steve

The major question is how often it will be removed and replaced in service. The form tapping will work-harden the 12L14 and orient the grain so it will be stronger and more wear resistant.

If there is no requirement to increase the strength (and if you are using 12L14, I would suspect that strength is not a primary concern) then keep using the cut tap.

Enjoy, DoN.

I hear this "formed threads are stronger" argument a lot. My thinking is if your design is such that the small difference between a cut and a formed thread makes a difference between success and failure maybe you should rethink your materials or design.

In 12L14 I think it's a mute point.

Best, Steve

Why are you making it hard? You are cutting the butter of steels. Nice stuff, easy to machine. I have a small pile of bar ends that never cease to make me feel like I have a clue when turning the stuff. :)

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

Perhaps because it is for soft and stringy metals (according to the web description) which describes pipe materials more than most other metals. And for those which do fit the description -- that is where thread forming taps make sense in straight threads (though I'm not sure how well they could handle tapered pipe threads).

Enjoy, DoN.

Granted, considering the use of 12L14, the strength issue is not quite all there is....

....That said, the difference is pullout strength in even low carbon steel between cut thread and formed is actually quite high...

....I have a part that I make for a "local Department of Defense" near you....that's the US Navy, thru contractors...that used to be made with a 7/16-14 thread that we used a cut tap on...we played around with a form tap and the pullout force went from almost 1200 pounds of direct pull to fali to nearly 2600 pounds....

....base material was 1018 cold rolled....1" diameter....2" long....drilled thru and tapped halfway from each side...pull test was with eye bolts threaded 5/16" deep.

Your results may vary....but forming DOES make for a much stronger thread, I believe.

Mike

Curiosity -- how do you tap from each side and have the threads meet?

This is really inneresting! I wonder if this "pullout difference" is proportionally greater in still softer materials, like aluminum.

Indeed it does. Nearly all DOD high strength stuff requires formed threads these days, rather than cut ones, based on conversations with clients of mine such as Fasterner Tech....

One could not be a successful Leftwinger without realizing that, in contrast to the popular conception supported by newspapers and mothers of Leftwingers, a goodly number of Leftwingers are not only narrow-minded and dull, but also just stupid. Gunner Asch

Yes..it is. Though not as great a difference.

Gunner

One could not be a successful Leftwinger without realizing that, in contrast to the popular conception supported by newspapers and mothers of Leftwingers, a goodly number of Leftwingers are not only narrow-minded and dull, but also just stupid. Gunner Asch

Mebbe someone used the wrong tap drill??? :) :)

Apropos of Garlic et al comments, it would seem the diff is closer to 10%.

Another machinist I know did this same type of test, got a similar result from his recollection, and provided two cites, which show a max of 10%.

I don't know the specifics for individual materials. When I was a tooling editor I was supplied with a variety of studies and test results, and they did show wide variability with material types and states of initial hardness.

One phone call to a major manufacturer of thread-forming taps is worth ten days of guessing and speculation. The guys at Emuge were always especially helpful to me.

I dunno.... somehow I think if that 1200 vs 2600 lb result were typical, cut taps would be falling out of favor/use REAL fast....

I don't think it *is* typical.

The basic reason for form taps is that they're more productive. They last longer, and they don't produce chips -- the bane of production machining.

The stronger threads, initially, were an incidental benefit. Soon they became one of the prongs of their marketing story. When you deal with a company that makes high-quality examples of both cutting and forming taps, such as Emuge or any of several others, you should get an accurate picture of when to use them.

I'm curious if anyone has encountered a drawing where the use of a form tap is mandated because of the increased thread strength?

Best, Steve

That would be because I goofed....a little transpositional error....

....SHOULD have read 2100 vs. 2600

opps....sorry about that

I'll go hit myself with a wet noodle now.

Mike

There was no need for the threads to be matched up....there was some crossover at the middle, but it didn't matter...the part only had to have .875" of full form thread from each side...3/4" of the mating stud is all that threaded into the part.

And as I mentioned in another post in this thread...I messed up....I typed 1200 vs 2600....it should have read 2100 vs. 2600.

oops

Mike