Turning the bolt instead of the nut
Turning the bolt instead of the nut
(OP)
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?
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?





RE: Turning the bolt instead of the nut
RE: Turning the bolt instead of the nut
IF you're using elongation, not torque, to evaluate bolt tension, it shouldn't matter.
Mike Halloran
Pembroke Pines, FL, USA
RE: Turning the bolt instead of the nut
A point to make is that on large fasteners the particular lubricant used makes considerable difference in the require torque.
What stress in the bolt are you hoping to achieve?
What is the material?
RE: Turning the bolt instead of the nut
Ted
RE: Turning the bolt instead of the nut
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RE: Turning the bolt instead of the nut
RE: Turning the bolt instead of the nut
RE: Turning the bolt instead of the nut
Dik
RE: Turning the bolt instead of the nut
I was testing some 1/4-28 titanium bolts years ago only to find out the grease that the techs were using during assembly had essentially zero effect on the preload for a XX in-lb of torque, while a proper anti-seize resulted in a ~50% higher preload for the same torque.
If it is really critical, test your hardware.
RE: Turning the bolt instead of the nut
RE: Turning the bolt instead of the nut
Dik
RE: Turning the bolt instead of the nut
RE: Turning the bolt instead of the nut
We found over the years that if we used bolts where the head was turned, we lost a number of bolts due to damage while tightening. Our main culprit was a sledge hammer mechanic spinning an impact wrench while engaging the bolt.
It is lot cheaper to replace a buggered nut instead of a bolt.
RE: Turning the bolt instead of the nut
Also, the chances of unwanted bending may be higher with bolt tightening as opposed to tightening the nut.
RE: Turning the bolt instead of the nut
Is tightening a screw into a tapped hole different than tightening a bolt into a nut? I don't think so.
Ted
RE: Turning the bolt instead of the nut
...still on the bolt/nut issue, do you have an explanation for why bolted assembly loses all of the torsional stress but still retains most of the initial tension after the initial relieving that takes place post tightening?
RE: Turning the bolt instead of the nut
because the bolt has stretched significantly.
What would make the thread friction or wind-up higher for turning one end vs turning the other? Regardless of which end you turn, you need to overcome friction at the supported face of the fastener you're turning, and the friction between the bolt and nut. If you don't overcome both of those, then you don't turn the bolt w/r/t the nut (or vice versa).
RE: Turning the bolt instead of the nut
Windup is equal whether turning nut or bolt (assuming similar friction coefficient and contact area). Please see recent testing:
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or review technical documents like VDI 2230.
Regarding loss of torsional stress, it is due to microslip at the contact surfaces. You can find recent technical articles on this subject using Google Scholar or Scirus.
RE: Turning the bolt instead of the nut
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Hope this helps
RE: Turning the bolt instead of the nut
RE: Turning the bolt instead of the nut
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
RE: Turning the bolt instead of the nut
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 :)