# How pick gears that will hold for given torque?

• Chevreuil
In summary, the author recommends using an off-the-shelf gear that has the specifications necessary for the task at hand. If the torque is countered by only one tooth, it comes down to the wheel radius and the size of the tooth. Thicker gearwheels make a difference.

#### Chevreuil

Hello,

I was wondering if anybody could recommend a simple method to pick gears for a given task. I need to make a rough estimation to see if I'm off by more or less a factor of ten. The only method I have access to is very complex and hard to understand.

Cheers

Chevreuil
The easy method is to find an off-the-shelf gear that has sufficient specifications for the application you have.

Chevreuil
It will depend on the gear ratio and relative mesh configuration.
If the torque is countered by only one tooth then it comes down to the wheel radius and the size of the tooth as a short cantilever. Thicker gearwheels make a difference.
Give us some dimension and configuration specifications so we can be more specific.

Chevreuil
Thank you all, I ended up finding that my chosen gear was too weak, and I had to go for one with twice the modulus (i.e. with the cogs about twice as large).

http://www.hpcgears.com/pdf_c33/27.48-27.60.pdf

In this document, it is said that the maximum tangential force, in lbs of force, that a gear can take without succumbing to wear, is

(X_c * Z * S_c * F )/K

Where X_c, Z, S_c, F is a bunch of factors derived from the gears and their working conditions. K however, is described as "Pitch factor DP 0.8 power". What does that mean? Does this mean that K=DP^(0.8)? (exponentiation with the diametral pitch as the base and 0.8 as the exponent)

Yes it just means DP^0.8

This is a more comprehensive manufacturers guide to gear design :