While I was building the Robot Bartender for Two Bit Circus, I had to figure out an adequate backdrop for Gearmo. Our strengths lie with fancy LEDs, but how do we fill a space behind him. I had to find a solution that would be dazzling enough, yet do so on a budget. Someone in our group had the great idea of using scratch marks and engine turning to create some cool effects. We did a quick test using some stuff we had on hand and were blown away by the results. Some simple chasing LEDs create a strong sense of movement. All of those reflections give us a lot of bang for our buck.

Engine Turning is the practice of creating circular scratch patterns, usually with an abrasive pad or sand paper. The ways that the patterns overlap can create an appearance of fish scales. It’s a very classic metal finish, and can be seen on the nose of the Spirit of St. Louis.

The next challenge was to figure out the right pattern for the engine turning. Usually engine turning is done in a simple grid pattern, but we had a CNC router so why not take full advantage. A friend of mine wrote some code to generate Fibonacci spirals for making cool LED elements. I adapted this code to program g-code for our CNC router. I did a test on some smaller plate to see how it would turn out. The code worked well, but I wasn’t happy with the spacing, so I had to go back and make some changes to the parameters.

We knew we wanted some bigger swirls, so we sourced a larger scratch pad that we could put meant to be put in a drill. At 4″ it requires more torque than our router spindle could put out. The tests we did by hand proved that we would need a rigid setup to get the desired effect.

We removed the router spindle and strapped on an electric hand drill using some hose clamps. It worked great. I put the aluminum sheet on a furniture blanket to introduce some cushion into the process. The foam on the sander helped as well. We loaded up the tweaked Fibonacci spiral g-code and let ‘er rip. The sequence took quite some time to run, but that’s the beauty of CNC… sit back and relax, and let the robot do the work.

We cut out the what we needed from the spiral using the same CNC router. The end result is a gorgeously organic yet precise pattern. I find Fibonacci patterns so mesmerizing.

I installed the Fibonacci pattern into its housing and added the strip of LEDs that surround it. A simple chase pattern makes some pretty awesome patterns. There are more complex light patterns that give some great variety, but I didn’t film all of them. It’s really meant to be enjoyed in person.