# How pick gears that will hold for given torque?

1. Jun 1, 2016

### 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

2. Jun 1, 2016

3. Jun 3, 2016

### Mech_Engineer

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

4. Jun 3, 2016

### Baluncore

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.

5. Jun 7, 2016

### 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).

6. Jun 10, 2016

### Chevreuil

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)

7. Jun 10, 2016

### Nidum

Yes it just means DP^0.8

8. Jun 10, 2016

### Nidum

This is a more comprehensive manufacturers guide to gear design :

PS: I can't see anything wrong with the gear drawings that you Emailed . Your problem may originate in some quirk of the CAD program . Best thing to do is for you to draw your own gears to the supplied dimensions . Then you can be sure that you haven't got something silly like a scaling error from your CAD's interpretation of the downloads .

Last edited: Jun 10, 2016
9. Jun 10, 2016

### Chevreuil

Thank you very much! This guide looks great!

OT: Did you see their video ad? I'm getting really weird vibes from it, but it really gets the message delivered.