Torque specs for screws

Sam

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Nov 15, 2001, 12:27:38 PM11/15/01

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Hello:

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?

Thanks!

Sam

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Robert Farmer

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Nov 21, 2001, 7:47:00 AM11/21/01

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Go to http://www.spstech.com/unbrako.html and download their engineering
guide. It has much information like formulas, joint diagrams and tables for
screws #0-3" (socket head cap type). Lots of additional info also.

Robert Farmer

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Robert Farmer

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Nov 21, 2001, 7:53:57 AM11/21/01

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I just remembered, NASA has a fastener design manual #RP-1228. It is loaded
with data. Try doing a search for it as many sites either link to it or
enable you to download it from them. It is rather large (~10 meg).

Robert Farmer

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David H. Neumann

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Dec 8, 2001, 5:32:20 PM12/8/01

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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.

David H. Neumann

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Dec 10, 2001, 5:32:54 PM12/10/01

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Bob K 207 wrote:
> Shouldn't the thread pitch somehow figure in there also?

Thread pitch p does affect the answer slightly, but is usually ignored
because the torsional resistance of the bolt is greatly dominated by
thread coefficient of friction mu (for typical, high friction values,
that is) as well as bolt head or nut washer face friction mu2, far
more than the slight mechanical advantage of the slightly-reduced
inclined plane of a fine-pitch thread.

The best answers explaining this phenomenon I've seen so far, which I
found to be right on target when one computes the Shigley, Mech. Egrg.
Design, 1989, K equation (Eq. 8-19), are
http://groups.google.com/groups?selm=337FB3...@lut.fi and
http://groups.google.com/groups?selm=01bc607d%24cf910ee0%242c5c2dce@Ptestware.