Calculating max allowable torque

[vector victor]

I would like to determine how much torque a pair of pins can handle.
I am using the pins to transmit torque from one rotating mass to another, as part of a shaft coupling. The pins are pressed into one half of the coupling and the other half has two toleranced holes that accept the pins and the two halves are flush against each other when coupled.
I'm given the double shear load rating of one pin at 40,000 pounds. The pins are each 3" from the center of rotation. Now torque being radius x force, would not one pin be rated at 3" x 40,000 pounds? But that seems too high a max torque, so I don't think I'm working that out correctly. What calculation would you use to determine the max allowable torque?

Thanks in advance.

[PinkertonD]

Ft-Lbs ???

[vector victor]

I'm using in-lb in this application, since the gearbox torque is rated in in-lb.

[PinkertonD]

3" = 1/4-ft

[jibberjabber74]

I would convert it to the si units of Kg and Metres, Which works out to be 136 Nm. To see if it that looks more reasonable (I am new to the job, so if I am talking rubbish let me know)

[PinkertonD]

Well, the way I would do this would be to start from the other end. Take the max torque available with a sudden crash-stop a second before the motor burns out and the breakers pop and calculate the max force that can be applied to the pins on a 3" radius.

I'd multiply that by 3+ (shock-loading during normal running, maybe 5+) as a safety factor and providing the shear shear failure is below that figure, go with what felt and looked right.

"Looked right?" Yes, I have had designs questioned because they didn't look strong enough even though I was certain the figures were correct. It cost me nothing to convert 1/4" diameter to 3/8" and apply a consenting (but not too condescending) verbal agreement. The customer/boss/etc is always correct. "Yes?"

p.s.
I am not a fan of two drive pins on anything rotating. For projects such as yours, I like 3+ and always odd-numbers of pins etc. Do it once, do it right.

[Kelly_Bramble]

I would like to determine how much torque a pair of pins can handle.
I am using the pins to transmit torque from one rotating mass to another, as part of a shaft coupling. The pins are pressed into one half of the coupling and the other half has two toleranced holes that accept the pins and the two halves are flush against each other when coupled.
I'm given the double shear load rating of one pin at 40,000 pounds. The pins are each 3" from the center of rotation. Now torque being radius x force, would not one pin be rated at 3" x 40,000 pounds? But that seems too high a max torque, so I don't think I'm working that out correctly. What calculation would you use to determine the max allowable torque?

Thanks in advance.

First off, each pin is only seeing single shear at applied loading.

You need to calculate the maximum shear loading each pin can take from the pin materials minimum characteristics.

See: https://www.engineersedge.com/materi...ear-stress.htm

Then, using that maximum shear stress before yield determine the maximum torque. I would use a FOS that makes sense though.

See: https://www.engineersedge.com/analys...ety-review.htm