Jam Nut Torque Value
Jam Nut Torque Value
(OP)
I have not been able to find much information regarding torque values applied to jam nuts, so hopefully this discussion will share useful knowledge.
Situation: I have two pieces of material that rotate about each other via a shoulder bolt. The shoulder bolt gets torqued to 55 ft-lbs into part "A", and part "B" rotates on the shaft of the shoulder bolt. The current design has a jam nut applied to the back end of part "A" to prevent backing out.
The orientation of components is:
Jam Nut--Part "A"--Bearing--Part "B"--Shoulder Bolt
Currently the jam nut is also torqued to 55-ft-lbs as well, but we are failing the threads inside the jam nut 40% of the time.
Should the jam nut be torqued to a percentage of full load? If so, how is this calculated?
Note: A jam nut is being used as opposed to a standard nut due to clearance issues.
Situation: I have two pieces of material that rotate about each other via a shoulder bolt. The shoulder bolt gets torqued to 55 ft-lbs into part "A", and part "B" rotates on the shaft of the shoulder bolt. The current design has a jam nut applied to the back end of part "A" to prevent backing out.
The orientation of components is:
Jam Nut--Part "A"--Bearing--Part "B"--Shoulder Bolt
Currently the jam nut is also torqued to 55-ft-lbs as well, but we are failing the threads inside the jam nut 40% of the time.
Should the jam nut be torqued to a percentage of full load? If so, how is this calculated?
Note: A jam nut is being used as opposed to a standard nut due to clearance issues.





RE: Jam Nut Torque Value
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Jam Nut Torque Value
60% of yield is what most of our torques are based on.
I personally wouldn't want to depend on shoulder jam torque to assure bolt tightness in a rotating moving part situation.
rmw
RE: Jam Nut Torque Value
RE: Jam Nut Torque Value
See this link for some helpful guidance, or maybe an alternate idea. Section 5.3.4
http://www.hnsa.org/doc/nstm/ch075.pdf
RE: Jam Nut Torque Value
That is a lot of failures. You also might want to
search on this site for the use of jam nuts.
RE: Jam Nut Torque Value
I think a 3/8 inch bolt torqued against a sleeve with 1/2" OD and a well controlled length might be more reliable.
How does the bolt interface with the support structure or housing?
RE: Jam Nut Torque Value
RE: Jam Nut Torque Value
A jam nut should be torqued to 1/2 to 2/3 of that of a regular nut based on the thickness of the "jam nut". The 55 ft/lb torque is probably on the high side for a regular 1/2-13 nut, especially if lubricant is used.
But stand back and ask yourself why the nuts are failing. It is because the axial load on the threads is higher than the failure load for the nuts. Therefore, you either have to change the design.
Fastener strength should always be tested in the lab and not on assemblies that are shipped to customers IMHO.
TOP
CSWP, BSSE
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