.: week 4.waterjet cutter, nc mill :.

I wanted to make a computer-powered wall clock that uses a planetary gearing system. This was my first attempt at studying and creating gears. I decided to use the WaterJet because I wanted to make the gears out of aluminum.

After learning basics of gears and spending some time calculating how to make a 1:12 3-planet epicyclic gearing system, I made my first cuts on the WaterJet. I should have realized this before cutting, but it's impossible to get a 3-planet epicyclic gear with a 1:12 ratio. Here are the results of the first cut - the planets touched each other.

First try - epic fail.

So...I modified my design. I decided to make my clock into a kinetic sculpture. I decided on a 1:6 ratio, but I wanted to hold the annulus stable, resulting in a nice motion of the planets. The sun has 20 teeth, the planets have 50, and the annulus has 120. Therefore, when the planets are the output, the gear ratio is 1 / (1 + A/S), or 1:7. Here is a picture of my planetary gear:

Final Planetary Gearing System

For a finishing touch, I laser cut out some acrylic and etched my name and MIT's logo into the back:

A personal touch

The design files are available here:


Future Plans

I'd like to turn this into a fully-functioning kinetic sculpture powered by a motor and with LEDs inside. I will put an Infrared trip sensor at my office door and hook it up to power the sculpture. So when I get a visitor, the planetary gear will start whirring and lighting up!