Jam Nut with insufficient thread 4

[weab]

I have an anchor bolt subject to tension. I have enough thread for a single nut but not enough to engage the entire second nut. This is a 90mm diameter anchor bolt and I have about 75mm available for the second nut. I don't want to weld to the anchor bolt in lieu of a jam nut. Is there a rule of thumb, or better yet a reference, that states jam nut requirements? Or is full threading also required for this?

 

[MikeHalloran]

Use a thin nut for the jam nut.

Some interesting info about jam nuts:

http://www.du.edu/~jcalvert/tech/jamnut.htm

Mike Halloran
Pembroke Pines, FL, USA

 

[DAVIDSTECKER]

If you are going to the torque the nut to the customary proof load, I'd look into good old Loctite.
If it is only as tight as a man with a cheater pipe can get it the you may want to try something like a tab washer.

 

[unclesyd]

Look at figure 7 in part 1 of Rich Barrett's Fastener Design Manual. Be aware of the caveats in their use.

http://www.tcnj.edu/~rgraham/barrett/manual1-A.html

 

[dik]

Can you safety wire it? or peen the threads? or use a bent metal tab instead of the jam nut? I don't like using jam nuts because they tend to reduce the tension in the main fastener.

Dik

 

[youngstructural]

Hey Dik;

Just out of curiosity, are you in the pratice of placing your jam nut above your regular nut? When I read your post, I thought to myself "good point... Never thought of that", but I think we might both be wrong. If I interpret your concern properly, you are worried that as the jam nut tightens against the normal nut, it is in effect releaving stress out of the regular nut, and I would agree with you entirely were the jam nut placed above the normal nut in an effort to "lock it on". I just read MikeHalloran's post, which points to a University post regarding the issue, which indicates that the "proper" way of placing a jam nut would be to install it below the principle nut, thereby preventing your stress release.

Please take a look guys, am I wrong in thinking that placing the lock-nut below the regular nut will present the type of stress relief that Dik is concerned about?

Interested,
Regards,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[MikeHalloran]

I, personally, would be inclined to cross- drill the bolt and use a single castellated nut and cotter pin, or French locks, or Stage 8s, or drilled nuts and safety wire, or even Loctite, rather than jam nuts.

Every "Johnson Rod" that ever fell off a British motorcycle, i.e. every Johnson Rod ever installed on a British motorcycle, was "secured" with jam nuts.



Mike Halloran
Pembroke Pines, FL, USA

 

[dimjim]

A LOT OF ANCHOR BOLTS THAT I AM SEEING ON
LARGE LIGHT POSTS ETC SEEM TO USE THE
DOUBLE NUT METHOD. IS THIS IN THEIR SPECS.
jsdpe25684 (Structural) MAY HAVE TO FOLLOW
WHATEVER SPEC IS GOVERNING HIS APPLICATION

 

[weab]

More info. This is a huge crusher, hence, lots of vibrations, and in zone 3 earthquake zone in remote Asia location. In future, perhaps we will need to remove this piece and replace it, that is, we need to plan on reusing the anchor bolts. This is a specially designed foundation in confined area so removing and replacing anchor bolt is not possible, so I don't want to tamper with threads.

One other possibility - I have a second full size nut. What if I used it and tack welded it to the top of the anchor bolt (on the inside of the nut). If necessary later, we can gouge out the weld, remove the nut, and grind down the weld metal remaining on the first thread or so.

I'm remotely familiar with Locktite but never used it. Can nut then be removed later?

Don't think I could use cotter pin, nut would still back off some. Want to keep it tight.

My understanding is that most people wrongly put jam nuts on last instead of first. But if you don't really have to torque the bolt fully, then it doesn't really matter.

 

[weab]

Mike H.

Didn't really understand a castellated nut until now. It looks like a good solution if availble in 90mm dia. May need loctite or some other solution if not available.

 

[MikeHalloran]

I'm not a fan of welded nuts, especially if you plan to remove them someday, and more especially if you have to adjust them before someday comes.

On a crusher, I'd be inclined to drill the nuts and use safety wire _and_ Loctite.

Mechanics believe that blue Loctite is removable with a wrench, red Loctite is removable with a bigger wrench, and green Loctite is not removable. All are removable with a torch, i.e. at 400F or so, Loctite just decomposes.

There are actually many, many grades available, but your local distributor may not stock all of them. He will need your help in selecting the proper grade for your application. The size makes some difference, as does the finish, e.g. if the nuts or bolts are galvanized or plated.




Mike Halloran
Pembroke Pines, FL, USA

 

[dik]

Youngstructural... used to be one of those <g>...

By placing the jam nut below, and tightening it against the top nut, you are increasing the length of the grip a tad... this can only result in reducing the clamping effect.

I don't normally use jam nuts... their only benefit is in keeping the main fastener in place and if that's what's required, they work. I've often used Locktite as Mike has suggested... no downside that I'm aware of... also, a properly tightened nut should provide sufficient pre-load unless there is a vibration issue...

Dik

 

[weab]

Thanks guys. You've given me a lot to chew on.

 

[boo1]

eleminate the jam nut and add Locktite

 

[MintJulep]

If you really need to maintain preload, do not use:

Safety wire
Castleated nut and cotter pin
Lock tab washers

None of these have the ability to constrain relative rotation to zero, and hence all can allow a loss of preload. They are effective only in preventing the nut from falling off completely after the joint has failed.

Loctite, ny-lock type nut, or distorted thread nut.

 

[Screwman]

I would use high strength Locktite on the nuts. If you make sure that they are clean before assembly (spray with good degreaser) the parts won't come loose. With the high strength material you will need to heat the nuts up to about 450 degrees in order to break them loose for removal in the future. If you don't heat up the nuts the bond is so strong that you will twist off the stud before the nut rotates. High strength Locktite is very good stuff, I have never heard of a problem in a joint that was properly cleaned before applying it.

 

[unclesyd]

Take a look down the page at the information on Flexnuts. I would definately give Superbolt a call with the specifics of your application. They might have an even better idea in securing your crusher. Mr Rolf Stienbok who started the company used to enjoy a challenge and as I understand it the current people do too.

http://www.superbolt.com/Superbolt Catalog 2004 online edition.pdf

 

[dimjim]

This url was posted on another post and you
may want to check it out and simply use these
unusual washers and a heavy nut.

http://www.nord-lock.com/default.asp?url=51.16.37