[SOLVED] Delrin and Stainless 1/4 - 20 all-thread question

Right. That would be my first guess. A ordinary nut has a thickness of about 80% of the thread diameter. In this case the thread engagement is three times the thread diameter. Dan

You are wrong. It is exactly the strength predicted.

Basically

All of this means nothing to a statically loaded thread. Stress concentration due to the thread form will have absolutely no effect in this case.

Even if the thread

In the aerospace industry they are called "J" threads, as in UNJ thread form. They were designed to increase fatigue life by reducing the stress concentration. The effect on static load capacity is nil.

Grain orientation has got nothing to do with it. It is simply the rolling process which induces cold working into the stainless and in turn raises the ultimate tensile strenght.

Wrong.

I suggest your test data was flawed. No way are you going to get 3 times higher static load strength by changing the thread form from a standard truncation to a radiused root, not for a static load. The fatigue life can be greatly enhanced but as I said before, the static load is a function of the root diameter.

Then you had better take that up with the authors of the mechanical engineering texts, and specifically with Carroll Smith.

Go right ahead and use lathe-cut threads rather than rolled threads. You are correct they are just as strong. Please let me know if anything I ride, fly, or drive on has any of your design work in it.

Jim

I don't have the Carroll Smith book you refer to. But I do have several mechanical engineering texts.

only if the rolled thread of a austenitic stainless steel screw is fully annealed after rolling.

Please

I don't know what you typically fly on, but the chances are pretty good if it's military or commercial, and has a GE engine, its too late. You have already needlessly subjected yourself to my engineering. Why don't you ask a mechanical engineer at your place of employment to explain to you why stress concentration factors are not applicable to a statically loaded threaded member in pure tension. Perhaps you will believe it if you hear it from someone else.

I strongly recommend this book.

Stress concentration is *not* only about fatigue. Try snapping a few bolts with an instron. You will see the difference, depending on the thread type and fastener design.

Jim