Quote:
Originally Posted by GeeTwo
It depends on how much pushing you're doing, and (more importantly) how hard the collisions are. The case where you're most likely to need steel is on the bull gear (gear nearest the wheel) and the gear that engages it. It would take a truly extreme case to require steel gears in the earlier stages, or even on the bull gear for simple pushing without collisions.
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Quote:
Originally Posted by Chris is me
This is entirely conjecture. Properly aligned and sized for the application, in a drivetrain you should basically never fail an aluminum gear no matter how hard you're pushing. Maybe if your output gear is 14 teeth or something crazy like that you'll have a failure, but in normal applications you'll be totally fine.
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I agree with Chris - why not just run the numbers yourself instead of guessing?
Here is a great presentation on shear stress in a spur gear. Matweb should have material info on 7075 aluminum and 4140 steel (not sure how to apply allowance for the ceramic coating on the aluminum gears). See what safety factor your teeth have for each gear in the gear train for each material. The less robust the mounting, the more safety factor is needed.
-matto-