are to be torqued by a rotational angle vs. ft/lbs force. From reading an article in the January 2007 "Quality" Magazine I believe I have a better understanding:
1. "Threaded fastener analysis has shown that most of the energy applied goes into overcoming the friction that exists under the head of the fastener and in the threads." "Together these two sources can typically be as much as 80% to 90% of the applied torque energy, leaving as little as 10% of the energy to transfer into clamp load."2. "..the presence of dirt on the trheads can increase the amount of friction..." "...a drop of oil under the head of a fastener can reduce the friction and allow more energy to flow into the clamp load, which can overtighten..." 3. To solve this: "...measuring the turn of the fastener". "The angle of rotation of a threaded fastener is more directly proportional to the clamp load than the measurement of torque.". 4. "Because of the additional expense of angle measurement, the torque-turn methods are usually reserved for only the most crucial fasteners in an assembled product". FYI. Regards, Jim
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