I saw this while checking up on the progress of his selective laser sintering (SLS) project. Basically his idea was smaller power lasers might be able to cut through thicker material by “sawing” through it. The required power density might only be high enough at the exact focal point of the laser. Therefore, if you move the focal point through the material vertically, you might be able to cut it. He did it using a reciprocating motion, but you could also simply run the same outline at multiple levels, which is what us mill and router people have done for years.
The machine is actually a beautiful work of hacker art. He build it out of CD/DVD drives. He only gets about 1.5″ of travel on each axis, but that is all he needed.
While he did manage to cut a shape from a CD case with a 1 watt laser, there are probably some issues with this idea that need to be compared with other methods. Since the beam is in a cone, the edges of the cone need to cut material as the focal point moves down. Even a perfect TEM00 beam looses power rapidly at the edges of the beam. Also I wonder if his method might actually remove more total material than focusing at the center. He might need to remove a cylinder of material rather than an hour glass.
Regardless, I like following Peter’s work because he is not afraid to try ideas that other might consider silly. It is all good data to have.