Jam Nut locking device
Jam Nut locking device
(OP)
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?
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?





RE: Jam Nut locking device
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: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: Jam Nut locking device
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
www.heviitech.com
RE: Jam Nut locking device
RE: Jam Nut locking device
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
www.heviitech.com
RE: Jam Nut locking device
Have you looked at those threads?
KENAT,
Have you reminded yourself of FAQ731-376: Eng-Tips.com Forum Policies recently, or taken a look at posting policies: http://eng-tips.com/market.cfm?
RE: Jam Nut locking device
Ted
RE: Jam Nut locking device
Regards,
Kars
RE: Jam Nut locking device
http://www.boltscience.com/pages/twonuts.htm
Ted
RE: Jam Nut locking device
http://www.nord-lock.com/default.asp?url=51.16.37
Select a language to download the video.
Ted
RE: Jam Nut locking device
CODE
===================================
Forging http://mech.e.tripod.com
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Ddraig Breuddwydia....www.tailofthedragon.com
RE: Jam Nut locking device
www.slicinc.com
RE: Jam Nut locking device
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
RE: Jam Nut locking device
RE: Jam Nut locking device
KENAT,
Have you reminded yourself of FAQ731-376: Eng-Tips.com Forum Policies recently, or taken a look at posting policies: http://eng-tips.com/market.cfm?
RE: Jam Nut locking device
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.
RE: Jam Nut locking device
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
RE: Jam Nut locking device
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."
RE: Jam Nut locking device
RE: Jam Nut locking device
RE: Jam Nut locking device
rmw