I love gears, pulleys, and power transmission systems - but I've never actually taken a milling machine to the side of a lawn mower gearbox to find out what's happening!

(This is a single-ratio, variable speed transmission, no gear shifting)

Here you go.

Steps:
#1 Find old lawn mower
#2 Take it apart. Or better yet, work with your kids to take it apart.
#3 Take it apart and clean the grease out - very messy.
#4 Mill the side away
#5 Watch the gears work over and over. Because it's awesome!

Huge thanks to Dad, who always helps with tools and shop space.