Torque spec for jamb nuts

[saab007]

Hi - I am trying to find torque specifications for thin nuts. And also trying to find out how to calculate the torque.

I have found specifications for standard nuts but have not been able to find anything for jamb (thin) nuts. Can the same standard spec be applied to the thin nuts for the same material and thread size??

 

[EdDanzer]

Because of the short length, maximum torque is limited to shearing the thread. Our experience is locking with a jam nut is a very poor method. As a rule of thumb for torque, use a percentage of a regular nut height.

 

[strokersix]

I attended a bolted joint seminar several years ago. The instructor stated that jam nuts used for locking purpose should be installed first, then the heavy nut on top of the jam nut. I have thought about this at length and not been able to figure out the logic behind this. Can someone please confirm or refute this and explain the reasoning?

Sorry for hijacking the post.......

 

[RiBeneke]

If you draw a diagram of the forces involved, the structure face is pushing against the jam nut (installed first), and the heavy nut (installed second) is pushing against the jam nut from the other side. The net reaction force between the jam nut and the bolt threads may be quite low, depending on how much it was tightened initially. If it was only slightly tightened, and the heavy nut was then tightened against it, to lock onto the threads (since the idea is to lock them together onto the thread and prevent loosening), then the heavy nut will be transferring the sum of structure face force plus force between the nuts, into the bolt thread. Therefore the heavy nut, installed second, needs twice the amount of thread strength. The logic is there, but I have seldom seen it done this way.