Gear Ratios

[Sad Max]

So I am working on a little project involving toothed gears, and I need the formulas to work out how many teeth a wheel of a given diameter should have, in order to turn another wheel of another diameter at a selected proportionate speed, ie how many teeth need to be on a 6" diameter wheel, in order to turn a 3" diameter wheel three times for each turn of the 6" one. Like that.

Anyone know of a place to find the formulas to work that out, or, better yet, a software tool that would take the numbers and do he math for me...?

[filmburner]

I think the answer is in your question: The 6" gear needs three times as many teeth as the 3" gear to turn in 3 times for each revolution of the larger gear.

The circumference of the 6" gear is 18.8" and the circumference of the 3" gear is 9.4" assuming 6" and 3" were the diameters of the gears and not the radii. (C=pi*d), which means that the natural ratio between the gears is 2:1 not 3:1. If both gears have the same teeth per inch (tpi) then the 3" gear will only turn twice for each revolution of the 6" wheel. They'd have to have different pitched teeth to get the ratio you want. You'd need a 9" wheel to turn the 3" gear three times per revolution.

But this is all just me applying some simple math knowledge, I don't know if gears with different tpi can mesh successfully or not it maybe possible, so you'll need to look into that.

May I ask what the project is that you need these gears for?

[Sad Max]

These will be CG 'virtual' wheels for an animation.

But the math would be identical, from a real physical gear train, to a virtual CG one.

[chuck coburn]

You can't mix diametral pitches. Such as a 32 pitch with a 48 pitch.

Look at this, it's real basic. There's tons of info out there.

http://www.howstuffworks.com/gears.htm