Rack and Pinion Contact Stress 1

[dan838792]

New to the group and I am hoping I can get some advise on assessing the contact stress of a rack and pinion design. I'm using AGMA 2001-D04 (with help from Shigley & Mischke) and trying to take into account having a rack and pinion instead of gear and pinion. The pinion is not helical. A couple of the assumptions I'm making are that the rack teeth are flat, so the rack tooth radius is infinite. The speed is very low (this is for a hand powered linear actuator). And the load is not reversing (the rack will always have a load in one direction (2 - 113 lbs). Is this a reasonable approach or are there specific procedures/standards for rack and pinion designs?

Thanks,
Dan

 

[dinjin]

The contact stress will be greatest at the tip of the pinion and the lowest will be at the greatest contact depth point of penetration of the pinion in the rack. Using an infinite number of teeth for the rack seems like an spproach to estimate the stresses as you suggest. The tangential forces will be different at each of these radii at the tip and lower contact point.

 

[tbuelna]

With a spur gear rack and pinion, the limiting factors are usually bending stress at the pinion tooth roots and contact stress on the pinion tooth flanks. The correct approach to designing the gear teeth is to balance the contact and bending stresses in both the rack and pinion to provide equal fatigue life.