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Re: elastic stop nut torque multiplier?

To: <shop-talk@autox.team.net>
Subject: Re: elastic stop nut torque multiplier?
From: Marc Sayer <msayer1@concentric.net>
Date: Thu, 03 Jun 1999 16:18:47 -0700
> That's not what I was after.  My thought was that some of the torque
> applied is ``used up'' overcoming the friction of the nylon against
> the threads as the fastener is tightened.  (I.e. you cannot spin a
> nylok nut down a stud like you can a regular steel nut.)

The friction (at the threads) involved while torquing a nut down only
comes into play after the nut has been tightened down enough for the
threads to be pulling against one another. Then you run into the
friction of opposing threads sliding past one another under load. The
resistance encountered while tightening a loose nylock is something
else. In your example you are comparing a freewheeling nut with no force
pushing the threads against one another, to a nut where the nylon insert
is designed for a minor interference fit. This differential has nothing
to do with torque values required to get a particular clamping force. Of
course it takes more effort to turn the nylock than it does the
freewheeling regular nut. But once they are both tightened down, the
bolt/stud is in tension, and the threads are pulling against one
another, then the force required to turn a regular nut is often greater
than that for a nylock. The reason for this is that the friction between
steel and nylon is less than that between steel and steel, in most
instances. And most nylocks have fewer steel threads and/or the steel is
softer than a regular steel nut. Once you actually start to torque
something down (i.e. turn the nut/bolt while the bolt is in tension and
is applying a clamping load) then the friction of a nylock is less than
a regular nut and you must reduce the torque value for a given clamping
force. OTOH a grade C locknut (all steel) does increase the torque
required to get a given clamping force.  




-- 
Marc Sayer
Editor/Publisher
Z Car & Classic Datsun Magazine
http://zcarmag.com
Voice 541-726-6001
Fax 541-746-0863/726-6001

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