Gear Formulas?

[SadMax]

Could anyone recommend a source for the formulas needed to work out gear relationships?

That is, given one gear wheel of a certain diameter, and a second gear wheel of a different diameter, how many teeth are required to step the proportional rotation up or down by a given percentage?

If that sounded ignorant and mangled to you, then you probably know the stuff I need to find out...

 

[DavidD]

Hey,

I went through all of that when I built my follow focus (still in progress). I should have bought the gear box in retrospect, but I couldn't just give up. You do need to work out the ratio - should be 1:1, but beyond that, I have used to different sizes of gears and both worked remarkably well.