Anti Rotation in Nut with low torque to start with 2

[chris564001]

Hi,

i'm hoping to get a bit of assistance with stopping a nut from coming un-done if possible.

I have an application using a load cell which is being inserted into metal rod, and then pulled under tension. The load cell is inserted into a hole drilled in the rod and screwed in at the bottom end (loosely). The load cell has an external thread on the other end, which then has a nut placed on it and screwed down 'tight'.

my problem is that I cannot apply large amounts of torque to the load cell as it starts changing the output. But I also need it tight enough so it cannot come undone.

At the moment I have a nyloc nut on the thread (m20x1.5), I have tried using Nordlock washers but couldn't tighten the load cell up enough to get them to work.

the problem is I cannot measure how tight I am doing them up at the moment as I do not have a method of doing so.

But does anybody know of a good method of stopping a nut from coming undone when it isn't torqued up high to start with?

I cannot post drawings/images as its commercially sensitive.

thanks,

 

[Jboggs]

Use two nuts and lock them against each other.

 

[chris564001]

@JBoggs: We tried that but it did not hold.

 

[JNieman]

Have you tried any flavor of typical Loctite products?

 

[JNieman]

Oh, and since it's easy to reference and fresh on my mind...

http://www.eng-tips.com/viewthread.cfm?qid=408177

You could make something akin to the threaded clamp ring. I'm not sure if there are any off the shelf solutions for M20x1.5 but it'd be a good fix. Then you /can/ obtain the advantage of high torque/friction by tightening the 'nut'/ring in place, since the clamping bolt won't affect the load cell at all.

 

[1gibson]

Use two regular hex (not nyloc) nuts and tighten them against each other.

 

[hendersdc]

Castle nuts could work if you don't mind putting a hole through the shaft

 

[byrdj]

http://www.elesa-ganter.com/in/2/sp/9232/4/86/set-collarsfor-threaded-shafts/gn-706.3/eg/

 

[kjoiner]

Hello,

Adding onto byrdj's post, what about an internally threaded clamp on shaft collar? I see some available from McMaster Carr but they only carry sizes up to M16 x 2. That would allow good clamping force without damaging the threads.

Kyle

 

[hendersdc]

Looks like Misumi makes some that offer M20x1.5 threads. Link Only $8.47 and ships in 1 day.

 

[imcjoek]

Another option,

http://www.whittet-higgins.com/part.php?series_id=6

 

[verymadmac]

Safety wiring the nut should work if you have somewhere to tie the other end of the wire off to.