Gear design project and have chosen 25 Horsepower

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Discussion Overview

The discussion revolves around a gear design project involving a 25 horsepower system with specific RPM and gear ratio requirements. Participants explore how to determine the number of teeth for the pinion and gear while considering practical constraints and design implications.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant states the need to find the number of teeth for the pinion and questions whether this number should be chosen by the designer.
  • Another participant suggests that any number of teeth can be chosen as long as the ratio of teeth is 3, but notes practical limits due to stress on the teeth.
  • A different participant emphasizes the importance of selecting tooth numbers that are relatively prime to avoid rapid tooth wear, providing an example of how common factors can lead to issues.
  • One participant expresses curiosity about the relationship between common factors and increased wear, speculating that repeated engagement of the same teeth may contribute to this issue.
  • Another participant elaborates on the wear distribution, explaining that using relatively prime numbers helps distribute wear across the gear rather than concentrating it on a few teeth.

Areas of Agreement / Disagreement

Participants generally agree that the designer must choose the number of teeth, but there is a discussion about the implications of common factors and the practical limits of tooth numbers. No consensus is reached on the best approach to selecting these numbers.

Contextual Notes

Participants mention considerations such as the minimum number of teeth on a pinion to avoid undercutting and the potential impact of tooth wear based on the choice of tooth numbers.

Who May Find This Useful

Individuals interested in mechanical engineering, gear design, and those working on related projects may find this discussion relevant.

Jason03
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Im working on a gear design project and have chosen 25 Horsepower, 1750 RPM;s for the pinion, and a gear ration of 3.

My question is how do I find out the number of teeth for each gear?

I know the formula

M_g = Ng/Np = ng/np

which allowed me to calculate the output RPM;s of the gear to be 583

But I am not sure how to find the number of teeth for the pinion...or am I supposed to choose this number since I am the designer for this project?
 
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any ideas?
 


Theoretically you can choose any number of teeth you want so long as the ratio of teeth is 3.

Practically there is a limit due to stress in the teeth, just make the gears a sensible size so they mesh ok.
 


As the designer, you must choose the tooth numbers.

If you must accomplish this speed change in a single stage (two stages would be difficult to justify costwise) and if it must be exactly 3:1, then you have a design dilemma. Any number pair you choose will be such that they will have a common factor. For example, if you choose 15:45, then they common fact is 15. The problem with having a common factor is that it leads to rapid tooth wear. If you could shift off 3:1 slightly, then you could use 15:46 and avoid the common factor. Since 15 and 46 have no common factors, they are said to be "relatively prime" even though neither one is a prime number. For good wear characteristics, you would like to choose a number pair that are relatively prime.

The other thing that you need to consider it to avoid having too few teeth on the pinion. Too few teeth can lead to "undercutting," a malformation of the teeth as a result of the manufacturing process. Depending on tooth size, somewhere between 14 and 18 is typically the minimumn number of teeth on a pinion.
 


Well I never knew that having a common factor increased wear, why does it do that? I'd guess becasue the without the extra tooth the same teeth pairs of teeth would always mesh.

Every day's school day :D
 


It is precisely because the same tooth pairs engage repeatedly. Imagine that one tooth has a bit of grit caught in it. It works on the same teeth on the other gear over and over.

If the number of teeth are relatively prime, then at least the wear is distributed over the whole gear, rather than being confined to the same few teeth.
 

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