Spiral bevel gearset - preferred direction of rotation

[Bkerila]

Looking for someone with Spiral bevel gearset experience. My question: Would you expect an increase in the torque required to turn a Spiral Bevel gearset in one direction (say Clockwise) vs. the opposite (say CCW). The formulas that I can find say that the transmitted force (and thus the torque) should be identical in either direction of rotation, but that the Radial and Axial forces will be different. Shigley (3rd edition 1977 - Mechanical Engineering Design, pg. 491) states "The hand of the spiral should be selected so as to cause the gears to separate from each other and not to force them together, which might cause jamming." It then gives an example of a pinion being "forced" into the teeth of a gear if rotated backward.

My thinking is that this only affects the radial and axial forces and in turn the supporting bearing forces, but that the transmitted torque to "overcome" this internal gear meshing effect is rather insignificant.

Anyone?

Thanks,
Bob Kerila, PE

 

[diamondjim]

Bob,
I think you offered your own answer. Shigley
is certainly the expert. You will be applying
forces to the bearings in a reverse direction if
you reverse the direction of the drive. Helicals
work the same way.

 

[BrianDengel]

Shigley is correct. You design your bearings to absorb the loading outward. If the gear are driven in reverse, they will be forced inward and bind. Under low speed, low torque applications, this may not be a prolem, but in high speed, high torque applications, this will overload the gears and most likely strip the teeth on the pinion.