How to chose gear wheels respective to torque?

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Steam Captain
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How to chose gear wheels respective to torque?

Post by Steam Captain » Sun May 31, 2020 3:18 pm

Hello,

I've been looking into gear wheel sizing a lot, but the searches end with explanations of how the diametral pitch (american;english) or Modul (parts of Europe) is calculated as the tooth-to-diameter-ratio.

BUT my interest is to be able to calculate which diametral pitch or Modul and thickness I need to use for a given torque and max rpm without the gear shattering into pieces.
Is there any literature in english/italian/german I can find what I want to know? Or is there a rule of thumb I am not aware of, which would totally suffice to do the trick?

I don't care if the answer explains the diametral pitch or the Modul, because they can easily be translated into one another. I just need to know the sizing, no matter what unit is used.

My question is not necessarily limited to steam launch applications, but aims more for a general understanding of gear wheel sizing.

Thanks in advance to the nice community
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Re: How to chose gear wheels respective to torque?

Post by Steam Captain » Tue Jun 02, 2020 2:38 pm

I think I just accidentally found a website with those kind of information. It's meadler.de which has a whole lot of different machine elements in their online shop and they actually list all important measurements of their products and even list the moment the gear wheels are capable of transmitting. They offer plastic, brass, unhardened and hardened carbon steel and stainless steel gear wheels and it provides a good comparison. If I buy a hardened carbon gear wheel somewhere, I can check this site to get a rough idea of the momentum a gear wheel made of the same material can transmit. This is already sufficient for me.
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Re: How to chose gear wheels respective to torque?

Post by barts » Tue Jun 02, 2020 3:04 pm

Hi Steam Captain -

Note that gear train (gears meshing together to transmit power) design can be tricky, esp. when running at engine speeds and transmitting significant power. As a result, most people use completely enclosed gear boxes designed as a unit for such service. For tasks such as driving pumps, etc. on a steam engine, a more simplistic design is possible using tooth strength calculations and adequate factors of safety.

- Bart
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Bart Smaalders http://smaalders.net/barts Menlo Park, CA
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Re: How to chose gear wheels respective to torque?

Post by fredrosse » Tue Jun 02, 2020 3:25 pm

Gear design and selection is a rather large technical field, with dozens of physical considerations that will overwhelm almost all mechanical engineers. You can get a fairly reasonable perspective on the technology at the website below:

https://khkgears.net/new/

If you are not ready to invest at least a few hundred hours studying this technology, then you may find approximate answers by looking at the gear designs used in service similar to your intended application, at least as a starting point. In my experience, the use of pulleys and toothed belt drives (or conventional sprocket/roller chain drives) is a far easier selection process, and satisfactory for the great majority of applications encountered that do not involve mass production and very expensive development programs.

A neat video to get started: https://www.youtube.com/watch?v=Q-XOM4E4RZQ
Last edited by fredrosse on Tue Jun 02, 2020 4:03 pm, edited 1 time in total.
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Re: How to chose gear wheels respective to torque?

Post by cyberbadger » Tue Jun 02, 2020 3:40 pm

For reference I have used a few belts.

I highly recommend Gates PowerGrip GT4. I have not had one break on the water.

I know of at least one person in England who is running a geared belt.

This is what I use...
https://www.mcmaster.com/6486K651
Mcmaster Catalog# 6486K651
High-Strength HTD Timing Belt, 30 mm Wide, 1584-8m-30, Gates Powergrip Gt4
8mm Pitch, 30mm wide belt
[The wider the belt the more power it can handle, but the more you will pay for wider pulleys.)

The stainless steel pulley's are expensive, but you get what you pay for.

I do not recommend L Series Timing Belts. That's what I started with, and on my 3rd? outing the L series belt snapped and I realized that it couldn't handle the 6HP from my Toledo Engine.

I tried several ratios. I have one gear ratio in the chain from the engine to a jack shaft, then another ratio via the belt pulleys.

My ratio right now in the belt pulley's is 34 teeth/28 teeth.

Corrosion-Resistant HTD Timing Belt Pulley
Stainless Steel Bushing Mount for 30mm Wide Belt, 95.250mm OD
https://www.mcmaster.com/1230N3

As far as design, Gates has a "Drive Design Manual" for PowerGrip:
https://www.gates.com/content/dam/gates ... 5_2014.pdf

L-series failure on Nyitra - Nobody hurt (I believe the belt snapping knocked loose a union on the engine exhaust)
https://www.youtube.com/watch?v=9pv8b6AI04g

-CB
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Re: How to chose gear wheels respective to torque?

Post by Steam Captain » Sat Jun 06, 2020 9:32 pm

Thank y'all for all the information. Well, calculating tooth geometry and material characteristics would be overkill for our applications. I guess belts are a good way for me.
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