While we are on torque wrench discussion, I attended a "Fastner" workshop at
the Conclave in Indy this past summer. It was truly fascinating. One bit of
information I learned, and saw demonstrated with load measuring devices, is
how much strength a bolt loses after it is torqued only once! When you
torque a nut or bolt to specs the first time, you reach a certain level of
pre-load, say 17,000 ft/lb. If you loosen that same nut or bolt, then
retorque it a 2nd time to proper torque, it will pre-load only to about
12,000-13,000 ft./lb. And it drops with each successive loosening and
retightening. A real case for not reusing bolts in critical safety usages.
It made me think, and shudder, at the number of times a wheel stud and bolt
are loosened and torqued over its lifetime. Not very often do we change out
our wheel studs, but they have to be running at only a fraction of their
original strength.
--David C.
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