[TowerTalk] Lock nuts revisited

[Roger (K8RI)]

A while back we had a discussion on using lock nuts AKA jam nuts.
The thought experiment was proposed that explained the jam nut as no 
more than moving the bolt head down the bolt to a different location.  
To many that sounded logical and it sorta did to me at first until I 
happened to go to remove a bolt that was fastened that way. It wouldn't 
turn.  I was actually in danger of twisting it off.

So I ran some real experiments. Looking at it from the physics approach 
that jam nut does not work the same as the bolt head in a different 
place. For example, the bolt is screwed in to the desired depth in the 
threads and then the nut is tightened. When that nut is tightened it 
pulls the bolt straight out against the threads in the rotator, or 
objects base which adds force that adds to the torque required to remove 
the bolt with out torquing the bolt down tighter.  It may only take a 10 
to 15 ft lbs to remove the 1/4 or 5/16" lock nut, but the bolt takes far 
more torque to turn. So that lock nut does add a good deal of resistance 
against the bolt coming loose.  I was easily able to remove the lock nut 
with one hand on a short wrench. I couldn't turn the bolt  safely when 
the lock nut was tight.  There is much more to the explanation that this 
but  it did work unless some one has a different explanation.

I don't have an attachment for my torque wrenches so I can measure the 
torque used on the lock nut, but the difference between the torque 
needed to loosen the lock nut and loosed the bolt when locked was 
considerable.

Roger (K8RI - ARRL Life Member)
www.rogerhalstead.com
N833R (World's oldest Debonair)