What's new
What's new

How to choose a diametral pitch on a spur gear?

vipaq2

Plastic
Joined
Aug 19, 2016
Hey guys, first time posting. I looked around but couldn't find anything specific enough.

I am trying different designs for a rack and pinion set-up to go on a BAJA vehicle, and I am wondering what diametral pitch i should consider.
I know the formula to prevent a minimal number of teeth so there is no interference, but after that is there any path I should follow?

Lets say i am aiming for a 1.5in Pitch diameter, how do I know if a 30 teeth 20 DP gear is better than a 24 teeth 16 DP gear? The more i increase the smaller the teeth get so I suppose I shouldn't go too high since the BAJA is hitting a lot of obstacles...

Plus what hardness should I target if I want to try an aluminum design? I am sure it is possible with anodization to reach an acceptable goal.

Thank you all!
Vincent
 
I worked in a design office in the late 1960s that did a lot of gear design. The standard design procedure involved two formulae, one for tooth strength and one for wear. My 1967 copy of Mark's handbook shows a similar tooth strength formula, and calls it the Lewis formula.
Our design procedure was based on the belief that there was a minimum face width needed for wear, and that this width was independent of tooth size. So we always used the wear formula first to set face width, then used the strength formula to decide tooth size.
Any refinements of the tooth strength formula are not very important, because different applications had different "loading factors" (i.e., multipliers of the static load) that were large compared to any refinements of the strength formula. Unfortunately, I cannot tell you the appropriate loading factor for a Baja vehicle because I have never designed one. Perhaps 3 or 4 times the steady driving load would be a good place to start.
Don't expect anodizing to improve the strength of an aluminum tooth. An anodize layer is extremely thin (less than .001 inch) and further, is very brittle. I would expect the anodize layer on a gear tooth surface to disappear in a hurry.
 
Thank you for your answer, I should try to find these formulas and see where it goes!
 








 
Back
Top