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Re: Rolled Threads

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>>> . . . by the way I believe that you are supporting my position that very
few
structural engineers have read ANSI B1.1.

If it's any consolation, not many fastener engineers have read it either.
The few of us who 'have to' do so only when necessary, as specifying (or
worse --- measuring) the complex dimensional characteristics of an inclined
plane's helix wrapped around a cylinder is a well-known source of conflict.
(Started, no doubt, by those guys in QA with their gauge R&R studies!)

I'm not sure I grasp the original concerns here, but if it's any help,
rolled threads are considered to be 'superior' in the fastener industry.
And, rolled after heat-treatment would be the cats meow.

Standard boltmaking practice (ANSI/ASME B18.2.1) is to manufacture bolts
from wire rod with a diameter slightly greater than the diameter of the
bolts to be manufactured --- with the maximum being a very small margin over
the minimum.  Thus, for a 1" diameter bolt the minimum would be 1.0000" and
the maximum would be 1.022".  So --- the nominal size comes from the
theoretical minimum, although no one would dare try making bolts from
1.0000" rod ---- because they would be unable to hold that dimension once
they thread it --- by rolling or cutting.

Why?  Because the 'major diameter' (top of the thread) minimum is identical
to the nominal size.  As a practical matter, one can't cut or roll theads
onto a cylinder and retain its exact original diameter.  If you could, the
bolt threads would be sharper than a surgeon's knife.

Most bolts have their threads rolled onto them moments after they come off a
boltmaker and they pass through opposing dies which form the threads in a
compressive fashion.  No material is removed, and what are generally
accepted as beneficial stresses are created in the thread regions.  Also,
the grain flow is different and provides beneficial properties.
(particularly under dynamic service loads)

Cut threads are done via removal of material, and are associated with
typically less favored characteristics ---- ranging from a general inability
to control the shape of the thread 'root radius' ----- to far more scatter
in any torque/tensioning based tightening methods, if used.  The dimensional
requirements for either method are the same.  If one doesn't have a copy of
ANSI/ASME B1.1 handy, an abstact of it can be found in the Industrial
Fastener Institute's "Fastener Standards" book, 6th Ed.

If it's any help, it doesn't matter whether one is concerned with tensile or
shear properties.  Either way, we in the fastener industry base our
assumptions about strength on the 'stress areas' in our standards.  Such
values are the same for cut or rolled conditions.


David Sharp
TurnaSure LLC -- NYC Office
57 E. 11th St. 8th Fl.
New York, NY 10003







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