Turnbuckles and Torque?

[Richard1957]

I'm a designer and not an engineer so excuse me if this a simple question.

If I have a basic stud and nut and a given load I need to induce in the stud I can determine the torque required to produce that load.

In the same situation, if my setup is similar to a turnbuckle, one stud and two nuts with left and right handed threads, what happens to the torque requirement to produce the same desired load in the stud?

Any help would be greatly appreciated.

Thanks, Richard in Houston

 

[desertfox]

Hi
I would place one nut on one end of the stud and pass the stud through the components to be clamped, then put the nut on the other end but ensure there is no rotation of the stud orbthe nut you placed on the stud originally and tighten the last nut you placed on the stud to the torque required to produce the bolt load as though it were a single nut and bolt

 

[drawoh]

Richard1957,

A working assumption in a lot of bolt torque calculation is that the bolt is very much more elastic than the joint. If your turnbuckle is attached to a cable, I would assume that the cable is way more elastic than your screw. This is a completely different calculation.

If there is no cable, you have two devices generating friction. In a bolted joint, most of your torque overcomes friction. Torque is not a very accurate predictor of how your joint works. This will be that much more true with your turnbuckle.

--
JHG

 

[Richard1957]

Thanks for the replies.

If it helps I'll try to explain my application a little better.

If have two hubs to be mated together.
I have a two piece clamp (basic circular shape) that closes around the OD of the hubs.
The clamp hinges around at pin on one side.
180 degrees from the hinge pin each clamp half has a "trunion nut", one left handed thread the other right handed.
Each nut is fixed inside the clamp and they cannot rotate.
The stud runs thru the nuts and the clamp is open or closed by turning the stud.

I completely understand the limitations of using torque to apply or to verify the load in the stud.

Now back to my basic question.
Ignoring all outside factors and assuming a perfect world, if I apply a given torque to a single stud and nut setup it will produce a load in the stud.
If I have the same target load for the stud in this "turnbuckle" type of application what torque value do I need?
is the torque value the same, is it halved, is it doubled?

Thanks again.

 

[desertfox]

It's the same torque as for one bolt which is what I indicated in my first post.

 

[drawoh]

Richard1957,

I think your clamp will be way stretchier than your stud. Standard screw torque calculations do not apply here. It may be elastic enough that you can tighten it snug, then count turns of the nut. Check your tolerance stack and see if you can measure the gap between the ends of your clamp.

--
JHG