I considered building a robot that makes candles. This would be done by dipping the candle in different colored wax using some sort of overhead gantry to create a multicolored effect. Then using some sort of CNC lathe to create different diameters that would show off the different colors.
Then I get on YouTube, a natural source for learning and ideas. I didn’t find any real good “How To” videos, but I did find one interesting video. Someone actually turned the task of dipping candles into a sort of kinetic art.