Thread "slipping" problems

[Amihai]

Hello,
When trying to thread two pieces together tight, some of my threads will sort of "slip" on each other, and no matter how much I keep engaging them, they won't stop spinning and won't lock on each other. What can cause such a problem and how would you solve it? My threads are made from Ebonite, if that matters somehow.

Thank you very much,
Amihai Fishman.

 

[Oliver X]

Typically, when threaded components spin after being tightened, the threads are stripped. It could be you're applying more torque than the threads can handle or the threads aren't sized correctly or they lack sufficient form. Ebonite is fairly soft in the grand scheme of things. It takes threads well and they'll last if treated properly, but fine threads can be stripped rather easily. It's also possible the wall thickness isn't sufficient to maintain strength.

Can you provide any more information such as what type of part, thread size, method of threading, major diameter of external thread and minor diameter of internal thread and wall thickness of the threaded area?

 

[Amihai]

Typically, when threaded components spin after being tightened, the threads are stripped. It could be you're applying more torque than the threads can handle or the threads aren't sized correctly or they lack sufficient form. Ebonite is fairly soft in the grand scheme of things. It takes threads well and they'll last if treated properly, but fine threads can be stripped rather easily. It's also possible the wall thickness isn't sufficient to maintain strength.

Can you provide any more information such as what type of part, thread size, method of threading, major diameter of external thread and minor diameter of internal thread and wall thickness of the threaded area?

Wall thickness is probably my issue. It's a- M10X0.75 single lead thread between the section and the barrel. I use taps and dies to cut my threads. Thanks!

 

[Oliver X]

I'd personally suspect the amount of thread form as well. You might need to drill your barrels a little smaller or make the tenons a tiny bit larger.

 

[randyrls]

Amihai; As others said; the thread engagement (TE) may not be enough. TE is specified as a percentage. It can be as low as 50% and as high as 80%. The more coarse the thread, the lower the TE can be. The softer the material, the more TE you need for a tight thread.

Try making a test piece with no hole in the male threads, and lots of material in the female threads and see if the problem persists. Some dies have a set screw to change the engagement percentage.

 

[Hippie3180]

Yep, learned about that set screw.

Do you use a tenon cutter, it's nice because your tenons are always consistent with every pen. A slightly small or irregular tenon can through you off.