bolts that back out...why?

[jimg]

Ummmm....hold on guys. re: path of least resistance. I recall several times having bolts tighten to the point of busting a gut to loosen them. I mean those suckers really wound themselves into the hole to the point of needing a LONG cheater bar and lots of grit to move them. Guess it was induced by the direction of rotation of the part...just a guess on my part. Anyway, there was nothing least resistance at those times!!!

 

[BTDT]

In pre-Loctite days, (so I've been told ), there were little stamped pieces of metal with a tab sticking out, that the bolt would go through, and when you got bolt/nut tight, you would bend the tab up against the flat side to keep it from loosening. I've seen these on axle bolts on trucks, u-joints, etc.

 

[bx23barry]

In pre-Loctite days, (so I've been told ), there were little stamped pieces of metal with a tab sticking out, that the bolt would go through, and when you got bolt/nut tight, you would bend the tab up against the flat side to keep it from loosening. I've seen these on axle bolts on trucks, u-joints, etc.

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[john_bud]

Bolts loosen up in the inverse proportion to your ability to retighten them. Easy bolts that are right out in the open will nearly never loosen up. Bolts that require major dissasembly just to feel, will practically fall out after the first bump!

That's my story - and I'm sure I didn't forget to torque or add loctite !
(well, pretty sure anyway!)

jb

 

[mlauk]

The threads should be clean when installing a bolt. The bolt should be torqued properly based on the size of the bolt and the material, ie grade 8 bolt requires more torque than a grade 5 bolt. The proper torque keeps the bolt from over stretching and puts tension on the threads so they don't back out. Any kind of locking device also helps such as a lock washer, lock nut or a thread sealer.

 

[shaley]

A good, short presentation on bolt proof stress.
http://www.utm.edu/departments/engin/lemaster/Machine Design/Notes 29.pdf

 

[RobJ]

This thread also reminds me of the "where does the grease go" thread.

 

[tallyho8]

Why is it that when I am changing a tire at my shop and have all my tools handy, the lug nuts seem like they are almost too loose. But when I have a flat on the road, with a stupid manufacturer supplied lug wrench, the lug nuts seemed to have tightened to the point of nearly breaking?

 

[SnowRidge]

Nobody mentioned the "dash of weld" method of locking the bolt or nut to whatever it is holding.

 

[zzvyb6]

Pulleys "walk", meaning they can have out of plane forces acting on the shaft locking point. Since a screw is a form of inclined plane, motion can develop as the thread is cyclicly loaded.

Best way to stop its effect is to put a point on the sheave bolt/screw and a dimple in the shaft. The point will maintain the position in spite of the pulley wobble. Normally a key is used to maintain pully drive torque, so the pointed fastener is only needed to maintain position, not to transmit torque.

And I an unanimous on this.