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# Min torque rating for a gear and pinion

## Min torque rating for a gear and pinion

(OP)
I have a pinion exposed to 100 oz-in torque and a gear exposed to 300 oz-in of torque (gear ratio of 3).
Does the pinion need to have a torque rating above 100 or 300 oz-in?

### RE: Min torque rating for a gear and pinion

Torque is simply a force times the radius.  The force is to be equal in both and the torque is simply dependent on the radius.
If the radius of the gear were 6 times the radius of the pinion, the torque of the gear would be 6 times the torque of the pinion.
Always look at the force on the tooth and not the torque.  Torque confuses a lot of folks.

### RE: Min torque rating for a gear and pinion

mtbnski7,

As dinjin notes, the tangential pitch line force is the same for both gear & pinion.  However, that does not necessarily mean the teeth on both gear & pinion are equally stressed. The bending strength will typically be higher for the gear teeth than for the pinion teeth.  If the mesh contact ratio is low, it is helpful to use profile shift to help equalize the tooth bending strengths between the pinion & gear.

Hope that helps.
Terry

### RE: Min torque rating for a gear and pinion

I think you answered your own question. If the pinion is exposed to 100 then that's what it should be rated at. The confusion seems to be the rating of the gearset/gearbox. when you stipulate a torque then, you must say where it is. eg, 300 oz-in output torque, and then if you know the ratio it's a simple matter of calculating the rest

### RE: Min torque rating for a gear and pinion

(OP)
Thanks, that's what I thought, I just wanted to make sure I was thinking about it right.

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