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nuckolls.bob(at)aeroelect
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 Posted: Wed Mar 31, 2010 4:57 am Post subject: Threaded fastener security |
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| Quote: | At 07:22 AM 3/31/2010, you wrote:
B: The laws of physics including a study of basic machines,
coefficients of friction and sliding forces tending to move down an
inclined plane will show that no threaded fastener torqued to design
values will rotate on its mate unless for some reason tension on the
bolt is relaxed or strong but transient forces vibrations) tend to
overcome the breaking coefficient of friction in the threads is overcome.
J: I agree. The only advantage of using a jam nut that I see is
that if the load on the bolt is relaxed, the two nuts will still be
tight against each other.
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Right. As Paul mentioned yesterday:
P: You are correct. The application of a jam nut for locking is only
applicable when one cannot wrench on the other end of the bolt. And
never in a critical application. An example that comes to mind is a
big relay where the bolt is molded into the plastic.
The jam nut makes sense when installed tension on the bolt
is intended by design to be much less than the strength of
the bolt. In this case the role of the threaded fastener
is more like that of a rivet. Very good in sheer, and moderately
useful in tension. The two nuts become something of a
"second head" of the same bolt.
Bob . . .
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raymondj(at)frontiernet.n
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| Posted: Wed Mar 31, 2010 1:30 pm Post subject: Threaded fastener security |
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FWIW, one application where the recommended locking mechanism is a
locknut is on the rocker arm studs on WW conversion Corvair motors. I am
not aware of any failures in this application.
Just another data point for consideration.
Raymond Julian
Kettle River, MN
Robert L. Nuckolls, III wrote:
| Quote: |
<nuckolls.bob(at)aeroelectric.com>
> At 07:22 AM 3/31/2010, you wrote:
>
> <fran4sew(at)banyanol.com>
> B: The laws of physics including a study of basic machines,
> coefficients of friction and sliding forces tending to move down an
> inclined plane will show that no threaded fastener torqued to design
> values will rotate on its mate unless for some reason tension on the
> bolt is relaxed or strong but transient forces vibrations) tend to
> overcome the breaking coefficient of friction in the threads is overcome.
>
> J: I agree. The only advantage of using a jam nut that I see is that
> if the load on the bolt is relaxed, the two nuts will still be tight
> against each other.
Right. As Paul mentioned yesterday:
P: You are correct. The application of a jam nut for locking is only
applicable when one cannot wrench on the other end of the bolt. And
never in a critical application. An example that comes to mind is a big
relay where the bolt is molded into the plastic.
The jam nut makes sense when installed tension on the bolt
is intended by design to be much less than the strength of
the bolt. In this case the role of the threaded fastener
is more like that of a rivet. Very good in sheer, and moderately
useful in tension. The two nuts become something of a
"second head" of the same bolt.
Bob . . .
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