Fully Threaded Stud

[BATman2]

Has anyone ever designed a stud connection (aluminum base metal. Stainless Stud) with a "jam" nut applied against the same base metal as the stud - i.e. drill and tap, apply the stud (with locite), then add a jam nut and torque to the value for stainless? This a box with 4 studs, one per corner.

That arrangement is inserted into a support plate and a another nut is added and torqued again. ( I believe this would unload the first jam nut, ) I also believe the jam nut is detrimental and may lead to excessive bending. The assembly is loaded in three directions, high shock and vib.).

Not my design.....but I'm trying to correct it before a failure occurs.

Boozer

 

[strokersix]

Boozer,

You might consider installing the stud with anaerobic adhesive, torque the jam nut and let the assmbly rest until the adhesive cures, then remove the jam nut and replace it with a spacer of adequate bearing surface area to prevent crushing of the aluminum and finish the assembly. This will allow better stretch of the stud and likely a more durable assembly.

Mike

 

[BATman2]

Strokerstix,

Thanks very much! By chance do you know of any good references for stud joint design?

Thanks again,
Boozer

 

[strokersix]

Boozer,

Try "An Introduction to the Design and Behavior of Bolted Joints" by John H. Bickford ISBN 0-8247-9297-1.

A mistake that I have made in the past is using long setscrews as studs. They are typically harder than screws or studs so they can bite into shafts and are not suitable for tensile loading. You did not say that you are doing this but I thought I would mention it anyway.

Mike

 

[SJLeemans]

I'm having trouble seeing why you need the jamb nut at all. If it is to preload the stud in the box, you can do the same thing with the nuts that you are using to attach the box to the mounting plate.

Perhaps I'm just not understanding the set up; but....

I see no reason why you can't just install the stud in the "box" with the loctite, then immediatly install the box against the support plate. If you torque the nuts that hold it to the support plate to the correct level (ie, the correct preload for the bolt, for the application) the whole thing will never come apart.

Is there a need for a space between the box and the mounting plate? If so, then I understand the use of the lock nut. It will preload the one side of the stud in the box. The mounting nuts will preload the other side. Also, the mounting nuts really won't degrade the preloading on the box side of the studs; and will actually perform better than a washer which can "swim" on you.

I'd use the lock tight on the mounting nuts (w/washers!) or use a crimped nut, etc. Otherwise, the loctite on the other end of the stud does no good. The sames goes for the adhesive mentioned in the previous post.

Overall, this will give you the best joint. Let me know if I am missing something here.

By the way - it is my opinion that the adhesive, while able to hold the stud in place, does little to keep the joint from separating. You HAVE TO preload the bolt. The loctite or adhesive prevent the stud from vibrating out of box; but do nothing to prevent the joint seperating due to cyclical loading.

I hope this helps.....

 

[BATman2]

SJLeemans,

Thanks for the information, it does help.

To clarify, The assembly is a box four studs and a jamb nut threaded down each stud to the box (which I now plan to remove, I agree with you). That mounts up to a plate / bracket, then a mounting nut with extra heavy washers is added PLUS a castle nut acting as a jam nut and a cotter pin through the stud.

I agree with you, the first (next to the box) jamb nut is of little value, nor is space required between the box and the plate. I plan to remove it. Everything gets loctite and torqued to proper "wet" values (plus a little). The stud will have high strength loctite. This box will live in a high shock and vib. environment under a rail car, and may go long durations (several months) without inspection, hence all the extra locking devices and higher torques.

I'm going to double check the stud engagment, I believe it could be a little deeper.

Thanks again,
Boozer

 

[SJLeemans]

I'm glad I could help. As far as going with a deeper hole - although there is a point of no return, it never hurts to go deeper when your parent material is softer than your stud. There are many ways that the preload can relax. Don't be afraid torque them past the "minimum" preload.

Here is a PPT file that I found that is a good general overview on the considerations for bolted joints:

http://www.hexagon.de/rs/vdi2230.ppt

Good Luck,

Scott