[TowerTalk] Lock nuts revisited

[Steve Hunt]

Roger,

OK I think I understand what you are saying.

In my layman's terms, when you torque up a conventional bolt some of the 
torque converts to a linear "stretch" force on the bolt (via the ramp) 
and some overcomes the rotational friction. Whereas if you use a nut 
there is much less rotational friction and most of the applied torque 
converts to linear "stretch".

I think I'll stick to the Comms engineering :)

Steve G3TXQ

Roger (K8RI) wrote:
Steve Hunt wrote:
> Roger,
>
> I'm no mechanical engineer - just a lowly communications engineer - 
> but I'm trying to understand the point you are making:
>   
This arose from the problem of bolts falling out of rotators and trying 
to find effective means of preventing that.
> Roger (K8RI) wrote:
>  
>> 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.     
> Isn't this exactly what happens when you tighten the head on a 
> conventional bolt? You turn the head but it can't move forward (because   
When you tighten a bolt the torque is the vector sum of a rotating ramp 
which is divided between rotational and linear forces.  The nut exerts 
the same forces on the bolt, but where the bolt fits into the case sees 
mainly the linear force which is that vector sum converted to linear but 
minus friction. (IIRC).  They used to run us through these problems in 
calc based physics.

HOWEVER the largest weakness of the jam nut as we are talking (Not the 
half thick ones) is the effectiveness of using a jam or lock nut depends 
very much on the user.  Using SS I've had them lock so tight I could not 
remove the bolt until the lock nut had been loosened while with new cad 
plated bolts (that arrive from the hardware store with a coating of oil) 
were almost completely ineffective.
> it's hard up against the washer or whatever) so it pulls the bolt 
> against the threads. I would have thought that for the same thread 
> pitch, the same torque on the nut or the head would result in the same 
> "stretch forces" on the bolt. The jam nut simply locks the first nut 
> to the bolt; so I still don't see that the situations are any different.
>
>   

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