How to calculate gear shear strength?

[Jake2465]

I am getting ready to place an order for some involute cutters in the 12DP size. I plan to make a little spur gear reduction drive for one of those 22hp Harbor Freight engines. My question is how to find if the size of gear (assuming its 4140 and has been heat treated) will hold up to the torque demand or not. I would try to stay away from the 14 1/2 deg PA and go for the 20 deg PA for some more root strength if I can find the cutters.

My intuition says I should make the gears with as large a pitch circle as I can without it getting ridiculous so the gear teeth are not torqued on as much. I do have an understanding of basic physics and vector algebra. But it would be nice to confer with someone that has run these calculations before.

 

[francist]

You might find some useful stuff here

"A Treatise on Gear Wheels" by George B. Grant

It was published in 1893 but it's up on Google books and may be a fun starting point. I did take a quick peak at it, but nothing exhaustive. Here's a clip that describes how to calculate a desired gear diameter for given horsepower...



Good luck!

-frank

 

[stupoty]

it's up on Google books

archive.org has it too.

Internet Archive Search: A Treatise on Gear Wheels

Stu

 

[DiscoDan]

Look up Lewis Factor Equation. Found mention of it in an old gearing book and a chapter on strength and durability of spur gears.

 

[Jake2465]

Look up Lewis Factor Equation. Found mention of it in an old gearing book and a chapter on strength and durability of spur gears.

Looks like the Lewis factor is using the pressure angle to get the component vectors so a calculation can be made. It seems that gear with higher pressure angles will put a higher load on the bearings.

 

[cbellanca]

All the information needed to calculate the power transmission capacity of spur gearing can be found in Machinery's Handbook in the gearing section. There are tables for safe stresses for various materials.

 

[vinnito1]

As already stated, Machinerys Handbook is a great place to start. The American Gear Manufactures Association, AGMA, has several published standards that would allow you to calculate the bending and contact stress. AGMA 2001 -D04, 908-B89, 2004-B89 have all the formulas and material properties to accomplish your goal. It will take some time to go through it all and set up the formulas. You will have to make assumptions about gear speed, applied torque, and other derating factors to get the answer your after

 

[Jake2465]

Thanks, everyone for the input. I have been meaning to get into gear cutting and making some of my own drives. I think I will place the involute gear cutter order this upcoming week. I am redoing my 4th axis so its reduction is taken care of with a Bayside precision gear head. After that is done, I can work on getting a mandrel and cutting some blanks.