Turning the bolt instead of the nut 4

[jerry1423]

I have always been told that when assembling a nut and bolt, that the nut should be the thing doing the turning, and the bolt should be held stationary.
I have never questioned this, but I really don't know the reason why that is.
We have a clearance problem where the bolt will have to be turned and the nut held stationary. This is a very large machine, and these are M72 hex bolts.
What are the potential problems that turning the bolt, instead of the nut, can lead to?

 

[hokie66]

Back to the issue of washers, for structural bolts, the hardened washer should be under the turned part, be it the nut or the bolt. Doesn't matter which is turned. The reason the washer is usually under the nut is because it is more common to turn the nut.

 

[tbuelna]

Depends on what type of "nut" is being used.

If it's a locknut, it's good practice to check the prevailing (or running) torque of the locknut to verify that the locking element is good. This is usually easier to check at the nut.

If it's a nutplate, barrel nut, or similar, the nut is inaccessible and obviously cannot be turned.

With the M72 thread specified, torquing that large of a fastener will likely require some sort of power assisted tool. Or other installation methods such as heating the bolt or hydraulically pre-tensioning the bolt.

As the other posters noted, with regards to friction, it shouldn't matter either way.

Good luck.
Terry

 

[carnage3]

coreypad, miketheengineer, and Mikehaloran are all right.
The problem with turning the bolt instead of the nut is that if you are supplied a torque spec from someone else for the nut being spun then depending on what friction modifiers are present at each end the propper torque could be different for the nut or the bolt head. Torque specs create notoriously bad variations in actual bolt tension. If you can measure strech and the tension is important then it is much better to do so.

Is tightening a screw into a tapped hole different than tightening a bolt into a nut? Yes, but that is an entirely more complex arguement