×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

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!

*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

Jam nut first or last.

Jam nut first or last.

Jam nut first or last.

(OP)
Does anybody know what should be installed first, jam nut over regular nut or the other way around?  I can not find any standards regarding this issue.  Any help will be appreciated.  Thank you.

RE: Jam nut first or last.

Thats a good question. Its been around for a long time and the instinct to tighten with the main nut and add a lock nut at the back of it, seems to rule everywhere, including as I have seen, slue rings on lifting cranes, etc. I understand this instinct is wrong, when you consider logic and Ajax Fastener Handbook. First, the lock nut, then the load carrying nut, tightened up the main nut to torque value and then back off the lock nut. The instinct way means the lock nut carries the load because it is pushing foward the main nut off the thread.

RE: Jam nut first or last.

Jam nut last.
It simply holds the load
nut in place and it only
stretches a short portion of
the thread maybe from the 1/3
from the center of the load nut
toward the jam nut and only sees
static load conditions.

RE: Jam nut first or last.

Having recently researched the issue of fastener integrity and was surprised how little logical information is available (compared to welding integrity)- I did come across this extract apertaining to use of Jam/Lock Nuts

LOCK NUT

There are two common usage’s of this term:

1.    A nut which provides extra resistance to vibration loosening by either providing some form of prevailing torque, or, in free spinning nuts, by deforming and/or biting into mating parts when fully tightened.

2. The term is sometimes used for thin (or jam) nuts used to lock a thicker nut. When used in this way the thin nut should be adjacent to the joint surface and tightened against the thick nut. If placed on top of the thick nut the thin nut would sustain loads it was not designed to sustain.



Jam nuts. These nuts are normally "jammed" together as shown in Figure 7, although the "experts" cannot agree on which nut should be on the bottom. However, this type of assembly is too unpredictable to be reliable. If the inner nut is torqued more tightly than the outer nut, the inner nut will yield before the outer nut can pick up its full load. On the other hand, if the outer nut is tightened more than the inner nut, the inner nut unloads. Then the outer nut will yield before the inner nut can pick up its full load. It would be rare to get the correct amount of torque on each nut. A locknut is a much more practical choice than a regular nut and a jam nut. However, a jam nut can be used on a turnbuckle, where it does not carry any of the tension load.

Hope this helps

Trac

RE: Jam nut first or last.

This is a question that has bothered me for a long time!  I attended a bolted joint seminar a few years ago and the instructor stated that the jam nut goes on first, then the heavy nut.  I have pondered this ever since and can't come to a satisfactory understanding as to why.

Looking forward to some more responses!

Mike

RE: Jam nut first or last.

This was the subject of a previous thread:

Thread404-38708

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

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! Already a Member? Login



News


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close