shear pin - hole size effect?

[BrianE22]

We use a double slotted pin (pin pressed in another pin) to transmit torque between a shaft and gear. I'm trying to determine how much the press fit of the pin in the shaft and hub affects the shear stress in the pin. I know for thick body cylinders an inward pressure on the OD will cause shear stresses in the cylinder. What I'm having trouble with is whether those shear stresses add to the shear stresses the pin sees from torque. Any opinions?

 

[boo1]

try

http://www.engineersedge.com/calculators/machine-design/press-fit/press-fit-equations.htm

 

[Tmoose]

By Slotted pin, do you mean a roll pin (also called tension pin), like this?

http://www.nuttybolts.com/catalog/images/PRO-Roll Pin.jpg

 

[BrianE22]

Yes, it is a alotted roll pin (as opposed to a Spirol pin). We press a 3/16" OD pin inside a 5/16" OD pin. I did receive some helpful info from an engineer at Spirol. He said that if the shear planes (radial gap between shaft OD and hub ID) are less than .005" apart there will be very little effect on the shear strength.

I'd think there would be some adding of the stresses caused by the radial compressive load and the transmitted torque. My 3d stress analysis is marginal though. I'm in the process of testing some pieces with different hole sizes.

 

[unclesyd]

We used this pin arrangement in several drive systems. In our use of this type shear pin arrangement I sheared a lot of these stacks
in double shear. As you posted that pins have to a good fit. The gap between the shearing edges has to be a close as practical, I used 0.001" One thing missed on on a lot of shear pin installation device is that the hole edge has to be square. Any radius of the hole edge will increase the scatter of the shearing strength values.

 

[BrianE22]

Good info on the hole edge - that probably explains one thing we noticed: There's actually two items pinned to the shaft, a gear that inputs torque to the shaft and a drum that outputs torque (same torque and pins) from the shaft. We ream the drum and shaft as an assembly before pin installation but not the gear/shaft hole. The gear hole pin usually fails before the reamed drum hole pin.