Lemme try.... feel free to check math and logic.


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Posted by Chris Case [75.36.43.24] on Tuesday, February 12, 2013 at 00:00:43 :

In Reply to: winch shear pins/working load limit posted by Mark in WV [184.13.218.172] on Monday, February 11, 2013 at 18:57:08 :

5/16 pin has .08 square inches. Soft steel has a shear strength of about 40,000 psi, times that .o8, so about 3200 pounds, each side of the pin, so about 6500 pounds of torque, on a 1 1/4" shaft (?). The radius of .625 guzunta 12" 19 times, so that means that the pin will shear at 342 foot pounds of torque. Multiply by the worm gear ratio, 40:1 (?) gives us 13,700 foot pounds at the drum shaft. But the drum is only 6" (?)diameter, or 3" radius, so times 4, 50,000 pounds pull on the cable to shear the pin.

My experience is that you will stall the engine first, unless you are revving it to the max and popping the clutch? The engine makes about 100 ft/lb, the pto is geard down 5:1, so the pto shaft has about 500 ft/lb, enough to shear the pin.

So, the engine has enough torque to shear the pin but the cable ought to break first, in full throttle operation. Maybe.

Anybody here ever shear a pin?

And oh, there should be zerk fitting in the yoke of the pto/winch input. It's there to keep that joint from rusting up solid so the shear pin has at least a chance of working.



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