I meant to reply to the list with this, not just to Pat...
Gary McCormick
-------- Original Message --------
Subject: Re: torque vs thread pitch
Date: Thu, 04 Jan 2001 10:34:40 -0800
From: Gary McCormick <svgkm@halley.ca.essd.northgrum.com>
To: "Patrick J. Horne" <horne@cs.utexas.edu>
References: <200101041734.LAA19765@hank.cs.utexas.edu>
OK - now we're in my bailiwick - mechanical stuff. Sparky stuff is like voodoo
to me - I
just rely on the best advice I can find - but mechanical is my bread and
butter. The usual
calculation for the relationship between fastener size, torque and clamping
force is as
follows:
T=KDL, where
K is a coefficient of friction between the internal and external threads
(usually given as
0.2 for unplated threads, 0.15 for plated threads assuming oil lubrication in
both cases),
D is the nominal diameter of the fastener,
T is the torque in inch-pounds and
L is the screw tension.
Screw tension (clamping force) is not dependent upon thread pitch, however fine
thread
fasteners are stronger than coarse thread fasteners of the same basic size due
to a larger
tensile stress area (see "Machinery's Handbook, 22nd Edition", tables on pages
1216 and
1217).
The various metric and American Standard (SAE standard is the bolt itself, not
the thread
form) threaded fasteners that are used in the same location (depending upon the
date of
manufacture of the car) are of essentially the same basic diameter, so the
torque values
used would be the same.
Gary McCormick
Senior Engineer
Northrop Grumman Marine Systems
Sunnyvale, CA
Purveyors of submarine-based ballistic missile launching systems to the US Navy
and Her Majesty's Royal Navy since 1956, surface ship propulsion
and power generation systems vendor to the US Navy, including
sole source supplier of submarine propulsion to the US Navy.
"Patrick J. Horne" wrote:
> Let's get some basic information here. I purchased the Roadster repair
> manual from Dr. Datsun recently and noted that the torques in it are
> shown to be the same for both SAE and metric hardware (in the same location
> on the car). I always thought that fine thread (I.E. Metric) required less
> torque to produce the same amount of clamping as coarse (SAE) threaded
> hardware. Has anyone verified the SAE vs Metric torque relationships?
>
> Peace,
> Pat
>
> --
> - Support Habitat for Humanity, A "hand up", not a "hand out" -
> Pat Horne, Network Manager, Shop Supervisor, Future planner
> CS Dept, University of Texas, Austin, Tx. 78712 USA
> voice (512)471-9517, fax (512)471-8885
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