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Message from discussion Torque specs for screws

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More options Dec 8 2001, 5:32 pm
Newsgroups: sci.engr.manufacturing, sci.engr.mech
From: dhn...@yahoo.com (David H. Neumann)
Date: 8 Dec 2001 14:32:20 -0800
Local: Sat, Dec 8 2001 5:32 pm
Subject: Re: Torque specs for screws

Sam wrote:
> Some months ago I came across on Internet a table for torque
> specifications for smaller size screws. I am not able to locate
> this table anymore. Is there anyone out there who would know
> of a site that would have specifications of this type?

Perhaps try http://www.fandisc.com/tti.htm and/or
http://www.fastenal.com/resources/online_calculators/calculators.asp.
Fastener installation prestress sigma_i = pct(Su), where Su = bolt
material ultimate tensile strength (UTS), and pct = percentage of Su.
You can typically use pct = about 0.53 for unlubricated and about 0.57
for lubricated; and Su strength values can be found at
http://euler9.tripod.com/bolt-database/ or
http://www.americanfastener.com/techcharts.htm. Bolt installation
torque T = K(D)(pct)(Su)(Ats), where K = torque coefficient, D = bolt
nominal shank diameter, and Ats = bolt tensile stress area from, e.g.,
http://euler9.tripod.com/bolt-database/bolt-database11.html. For clean
steel on steel, many people assume K = 0.15 for lubricated (greased),
or K = 0.20 for "unlubricated" (thin lubricant film, as manufactured).
Typically K = about 1.33(mu), if mu = mu2, where mu = thread
coefficient of friction and mu2 = bolt head or nut washer face
coefficient of friction. Good luck.