×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Jam Nut Torque Value

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.
 

RE: Jam Nut Torque Value

If you are torquing the shoulder of the bolt against Part A, you shouldn't need a jam nut. The function of the jam nut is to have something for the regular nut to be torqued against when it is not tightened up on the substrates. Torquing the shoulder against Part A is the equal of tightening up on the substrates.  

Michael.
Timing has a lot to do with the outcome of a rain dance.

RE: Jam Nut Torque Value

You don't say what size the fastener is so it is hard to tell if 55 ft-lbs is a lot of torque or too little torque.

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

(OP)
Shoulder bolt and jam nut are 1/2-13 thread.

RE: Jam Nut Torque Value

Jam nuts or double nuts are generally more complicated than what you would think, and I hate using them, or seeing them being used.

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

What grade are the fasteners,nuts, and jam nuts?
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

Is the jam nut failure the only failure, and does it occur at assembly?  

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

If these are indeed grade 5 quality, I would use the ratio of the heights times the torque value for the jam nuts as a maximum torque value.

RE: Jam Nut Torque Value

You are using a "jam nut" as the main and only load carrying nut and then wonder why they are failing?

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
www.engtran.com  www.niswug.org

"Node news is good news."

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources