Nut, Bolts and Threads

[Ray C]

Folks,

Here's a reading resource that I found years ago, lost track of -and rediscovered just recently. I find this to be a rather elegant, clear and fundamental explanation about threads. Short and very easy to digest.

Enjoy...

Ray C

 

[bluechips]

Good read, thanks.

 

[Dave Paine]

Very interesting, thanks for posting. I had read that the loads in the thread are mostly in the initial threads. The article mentions in a 7/8-9 bolt the first thread engaged carries 34% of the load. Wow, a lot more than I expected.

 

[RJSakowski]

Very interesting, thanks for posting. I had read that the loads in the thread are mostly in the initial threads. The article mentions in a 7/8-9 bolt the first thread engaged carries 34% of the load. Wow, a lot more than I expected.

A great article. Thanks for sharing. Definitely one to save in my "vault of knowledge".

Re: thread load, this is what I would expect as the bolt will stretch under tension with the stretch proportional to the applied force. As the threads absorb part of the load, the stretch decreases so the load on the remaining thread becomes less. An interesting observation is that 73% of the load is carried by the first three threads. I have long heard the axiom that a fastener must have at least three engaged threads. From the article, I would conclude that three threads will provide 73% of ultimate strength.

As far as fastener failure goes, I have had many fail with almost all of them a separation above the threaded region by applied tension and/or twisting. Even with bolts threaded into aluminum, this was most often the case. Stripped threads were most often due to cross threading or dirty threads. Wood and plastic were the obvious exceptions.

 

[RLE]

A great article. Thanks for sharing. Definitely one to save in my "vault of knowledge".

.......I have long heard the axiom that a fastener must have at least three engaged threads. From the article, I would conclude that three threads will provide 73% of ultimate strength.
.....

The ultimate strength is probably much higher, since with those three threads on there own, the more highly loaded threads, thread one for example, will yield slightly and allow a greater share to be taken up by two and three. And interesting thought is how much of a bolt load can be carried by a normal nut, which are generally much weaker material than the bolt and are less than one nominal diameter in thickness

 

[Ray C]

Pertaining to threads, here is another resource that is on the top of my list:

http://theoreticalmachinist.com/Threads_UnifiedImperial.aspx

Suggest you check the home page of that link as there are many other good calculators. I feel that most all of them are succinct and accurate.

Regards

Ray