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Old 25-06-2007, 20:29   #31
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Since the usual torque wrench uses a socket, and MUST be applied to the bottom nut first...

I would assume that conventional assembly tools and techniques only allow the installation one way: Torque down the lower nut, then tighten or torque down the upper nut.

IF the designer and engineer are aware that process is going to have to be used, everything else is a moot point. They can set the torque spec for the bottom nut--considering the changes that will take place after the lock nut is torqued down on top of it.

As long as you consider the entire forest rather than the design specs for a single tree...it'll be just fine.
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Old 26-06-2007, 01:07   #32
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No reason to use a socket on the prop nut you could elect to use a spanner with a torque wrench adapter.

Okay - I wrote this up yesterday and was afraid to post but here goes.

Ignoring friction losses for simplicity.

Nut one is installed with X torque. That torque creates 100 pounds of tensile load. The nut has 10 threads so there is 10 pounds of load per thread and the joint has 100 pounds of load.

Nut 2 is installed with Y torque. Y torque creates 120 pounds of tensile load. The nut has 20 threads. Each thread has 6 pounds of load. The joint has 120 pounds of tensile load. The faces of the two nuts have 120 pounds of load. The inner nut has -20 pounds of load on the threads or -2 pounds per thread.

is my physics wrong?
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Old 26-06-2007, 04:32   #33
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The proper way to use a jam nut
by Dr James B. Calvert
Associate Professor Emeritus of Engineering, University of Denver

”... The idea of a jam nut is to cause the two nuts to press on the threads in opposite directions, so that the thread is clamped between them, and this clamping is not relieved if the nuts should turn slightly on the bolt, so that unscrewing is discouraged. If this condition does not exist, and it usually will not be if the thinner nut is on top and tightened second, then the top nut and after it the lower nut can loosen without restraint, and there will be no locking action. Two nuts in this case are not much better than one. The proper connection is made by tightening the jam nut snugly first, then tightening the upper nut so tightly that the stress on the jam nut is reversed as the bolt strains. The two nuts could be the same thickness, but it saves space if the lower one is thinner. The thinner nut must counter only part of the compressive force of the regular nut, which does double duty ...”
Goto: The Jam Nut


Fastener Design Manual ~ by Rich Barrett
Fastener Design Manual -- part one
Fastener Design Manual -- part two
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Old 26-06-2007, 08:46   #34
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Quote:
Originally Posted by GordMay
The proper way to use a jam nut
by Dr James B. Calvert
Yo Gord,

good find on an understandable explanation!

best, andy
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Old 26-06-2007, 13:01   #35
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This thread makes my head hurt.....

Did all of you guys used to work for NASA??? Or maybe FEMA?

All I know is "righty-tighty, lefty loosey... except on submarines..."

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Old 26-06-2007, 13:54   #36
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I handed my wife the torque wrench and she applied it to my nuts. At 60 lbs I knew they were jammed. Some how I wasn't concerned wether the small one was on the top or bottom. Go figure.
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Old 26-06-2007, 15:45   #37
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Quote:
I handed my wife the torque wrench and she applied it to my nuts. At 60 lbs I knew they were jammed. Some how I wasn't concerned wether the small one was on the top or bottom. Go figure.
That'd bring tears to my eyes....arrrr... not sure, are we on the same subject still?
Quote:
except on submarines...&quot;
Huh???? are threads opposite or something??

Thanks Gord. OK I have learn't something.
Sorry I doubted you Andy.
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Old 26-06-2007, 20:56   #38
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Sorry I doubted you Andy.
Yo Alan,

no problem. Like I said, it isn't intuitive.

best, andy
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Old 27-06-2007, 00:18   #39
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"The two nuts could be the same thickness, but it saves space if the lower one is thinner"

I like this statement. I was having a problem with the "requirement" for one thin and one thick nut. It didn't make sense to me as it only impacts thread loads.

By the way my nuts are only rated to 60 inch pounds. But they are small.
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Old 27-06-2007, 00:34   #40
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I don't think it's the size of the nuts that count Dan ;-) So I believe anyway :-)
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Old 11-03-2010, 22:52   #41
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I did a survey at a yard today.....only saw one boat with the 1/2 nut against the prop.

That is the proper order right?

Fullnut-Halfnut-prop?
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Old 12-03-2010, 04:11   #42
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Quote:
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I did a survey at a yard today.....only saw one boat with the 1/2 nut against the prop.
That is the proper order right?
Fullnut-Halfnut-prop?
Correct.
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Old 12-03-2010, 05:14   #43
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Fullnut-Halfnut-prop?
I think you're halfnuts for bringing this thread back to life!
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Old 12-03-2010, 07:33   #44
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Could it be the case that it makes absolutely no difference which nut goes on first? Isn't the bottom line whether or not it holds? What if both ways hold equally well?
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Old 12-03-2010, 07:42   #45
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Yes, it matters, according to Dr James B. Calvert, Associate Professor Emeritus of Engineering, University of Denver, as quoted in post #33, Gord May, and others ...

The proper connection is made by tightening the jam nut (only) snugly first, then tightening the upper nut so tightly that the stress on the jam nut is reversed, as the bolt strains.
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