Jam Nut locking device 1

[lockingdevice]

There are many discussions on the web about the Jam nut below a normal nut. I have read some good analyses, but what I want to have is a well engineered Jam locking analyze. I have read that this device is better resist against vibration. This is because the thread in the Jam nut will deform. If this is true, you will not have the bolt elongation you want to have. This will mean that you will not reach the utilized yield strength you want. If I want to lock a diesel engine in a ship I have to pay attention to vibrations. To alleviate the vibration forces, my bolt elongation has to be a certain length and I think the bolt will not have his elongation with a jam nut below a normal nut.
Or will this jam nut lock by compression and plastic deformation? And after this deformation is the Jam nut not straight but taps?

Can anybody help me with this issue?

 

[CoryPad]

A fastened joint with a single bolt and single nut with standard threads (metric, UN) can be vibration resistant with enough preload. In fact, the simplest and least expensive method to resist vibration is to generate sufficient preload.

If you must use secondary features, thread adhesive is the best option. It provides excellent vibration resistance, it requires no special procedures, and it requires no extra analysis.

If you feel you must use a jam nut, then I would follow the advice of the late Richard T. Barrett (author of NASA RP1228 Fastener Design Manual). He recommends using a thin nut tightened first followed by a regular nut tightened second. This should develop full joint preload and have the two nuts locked against each other to resist vibration. An article on this subject was published in the American Fastener Journal within the last decade and should be available as a reprint. You can learn more here:

http://www.fastenerjournal.com

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[HeviiGuy]

Excellent advice, Cory:" the simplest and least expensive method to resist vibration is to generate sufficient preload " !

Nevertheless, here's a link to a European lock washer design (I've no affilation nor commercial interest with this company at all). It's nifty design:

http://www.nord-lock.com/default.asp?url=2.16.37

Ciao,

HevïGuy

http://www.heviitech.com

 

[25oak]

One concern to consider from an availability perspective is high strength jam nuts are rarely available. Designs with high strength fasteners are often assembled with the high strength nut against the bearing surface and the jam nut tightened on the standard nut as locking device.

 

[HeviiGuy]

Cory, shall you respond or, shall I?

Since I'm up at bat, I will...

Here's an intersting dissertation (not mine, alas):

"When a nut is torqued a deformation of the bolt threads take place. You can visualize that one nut, fully torqued will tend to deform the threads upward.

Now a half of a nut (the jam nut) will have less overall force than a fully torqued full nut. So if the full nut is placed on first, the threads are deformed upward. The jam nut, placed on top will bear against the full nut, tending to reverse the deformation. However since the full nut applies more force, the thread deformation under both the full nut and the jam nut is in the same relative direction.

If the jam nut is torqued first, the threads are still deformed upward. But when a full nut is fully torqued, the bearing against the jam nut will tend to reverse the thread deformation. The threads under the full nut are deformed upward, while the threads under the jam nut are deformed downward. This thread deformation reversal provides the locking mechanism.

The jam nut should be installed on the bottom."



Ciao,

HevïGuy

http://www.heviitech.com

 

[KENAT]

Cory probably has you covered but this type of question has come up on this site several times in the last couple of years at least.

Have you looked at those threads?

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

 

[hydtools]

The only thing I know a jam nut to be is a thick washer under the final nut actually carrying the bolt load. Double nutting is a waste.

Ted

 

[lockingdevice]

I think what Heviguy told about deforming the thread up- and downwards is true practically. But is this also proven on paper? You can find many theoretical analyses about this subject. But I have not found any arithmetic analyze. I have also read on this forum about some books about this subject. Does anybody now the titles / writers of these books? What I have also never seen is a test like the test of nord-lock or the junkers vibration test with a jam nut below a normal nut. If anybody have a test like this please tell me.

Regards,

Kars

 

[hydtools]

Here is a video made by Bolt Science:

http://www.boltscience.com/pages/twonuts.htm

Ted

 

[hydtools]

Here is the Nord-lock video:

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

Select a language to download the video.

Ted

 

[Pressed]

This is by the parent company, but it might get you something?

[URL unfurl="true"]http://www.flyupload.com/?fid=513882213[/URL]

===================================
Forging

http://mech.e.tripod.com

-------------------------------------------------
Ddraig Breuddwydia....

http://www.tailofthedragon.com

 

[railcarscott]

Also effective at maintaining clamp load is Disc-Lock. The make nuts with integrated washers and washer pairs. Very effective at resisting loosening forces due to vibration. We supply them for many railcar applications.

http://www.slicinc.com

 

[MikeHalloran]

Because of the environment (salt water, inevitably where you don't want it), mostly unattended operation at high power levels, and the likely consequences of failure (hole in boat when the last bolt falls out), you really need multiple lines of defense.

I.e., jam nut it if you want (I'd use lockwire), AND use threadlocker, both to prevent vibration- induced rotation and to protect the threads from corrosion.



Mike Halloran
Pembroke Pines, FL, USA

 

[Dinosaur]

I have been attempting to get my organization to use double nuts in some instances to prevent vibration from allowing the loss of clamping force. Initially I was working on having the jam nut installed first with the heavy hex nut installed against the jam nut. Then it occurred to me the cost was likely not significant in the overall scheme of things and I have been asking for double heavy hex nuts to eliminate confusion. We are still talking about this problem and no specific solution has been adopted as policy at this point. I recommend considering double heavy hex nuts to avoid confusion.

 

[KENAT]

Dinosaur, somewhere if not on this thread then in a similar one, there's a link to a piece about Jam Nuts. If I remember correctly, according to the theory of the piece, using 2 nuts the same size wont work properly.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

 

[johnSchwaner]

Dinosaur,

The link has a picture of a double nut on a suspension walk bridge over the American River in Sacramento, CA. Two heavy hex nuts of the same size. Some engineer thought it was a good idea.

 

[hydtools]

How tight would you make the second nut?
Not tight enough and there is no beneficial added friction.
As tight as the first nut then the first nut is unloaded and becomes just a thick washer.

If vibration is loosening the nut, then the clamp load is not high enough. Or the fastener is not long enough for sufficient elongation to handle the vibration cycles.

Ted

 

[Dinosaur]

Well, I am trying to obtain the function of a locking nut but avoid the confusion of which nut goes on first. With both nuts the same strength, it seems it shouldn't matter. I'm sure there are theoretical implications of how that changes the stress transfer, but it seems impossible to me that two nuts can not be as strong as one.

This does remind me of one of my favorite plan jokes ...

An engineer spnding a long time on his plan sheets is approached by his supervisor. The sup says, "What's taking so long?" The engineer replies, "I'm trying to make it idiot proof." The supervisor stands up straight and turns to leave saying, "Trust me, they'll just make a better idiot."

 

[Bribyk]

There's no such thing as idiot-proof, only idiot-resistant...

 

[rlee629]

The Nord-lok cam design has been proven to maintain clamp loads over time where vibration is present better than aerobic thread lockers or nuts and does not effect your elongation.