<VV> to torque, or not to torque

Spence Shepard sshepard5 at carolina.rr.com
Sat Oct 10 13:52:45 EDT 2009

The purpose of the fastener (bolt, stud etc.) is to clamp parts together by 
imparting a residual force between them. That is done by stretching the 
elastic fastener and keeping it in the stretched state. The fasteners are 
designed to be stretched to a point where they will provide a clamping force 
adaquate to hold the parts together. The force is a function of the 
characteristics of the fasterner including material properties and 
dimensions and can be calculated as a linear function of the stretch. The 
true measure of the clamping force is the stretch and the best way to 
determine the stretch is to actually measure it which is done on critical 
applications. Torquing is used as a more convenient way to approximatelly 
determine the stretch. There are several factors (mostly coefficients of 
friction) that affect the accuracy of that method.

The main problem with measuring stretch is that amount of stetch involved is 
very small and the accuracy required is often in the tenths of thousanths 
(.0001") of an inch. It is very difficult to obtain that accuracy, therefore 
torquing is used as a practical compromise.

Spence Shepard
----- Original Message ----- 
From: "lewisrishel" <lewrish at sbcglobal.net>
To: <virtualvairs at corvair.org>
Sent: Saturday, October 10, 2009 1:01 PM
Subject: <VV> to torque, or not to torque

> Many years ago, back in the dark ages, when  I was changing spark plugs on
> air cooled piston aircraft engines, it was usual for them to have engine
> mounting bolts that were 'torqued' by measuring how much they 'strecthed'
> by tightening. Reckon the folks at Izusu have finally caught on ?? Reckon 
> we
> could do the same with v air head bolts ??
> Lew
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