garylmast wrote:Although my laser is a 400 watt, I noticed the closer the nozzle is from the material it gives a narrower line. Sometimes when I'm cutting, the material is warped so I adjust the nozzle to clear the high point. I've noticed at the lower places, the cut is wider and sometimes has soot at the edges.
Yup. You probably know all about focal length. Suffice it to say that the longer you can set the focal length the less problems you will have with varying beam diameter. On my laser the focal length is 6 inches. The thing to remember with lasers is that they are not like cutting tools, the "keep that bit as short as possible" does not apply. Of course if it gets too long you can start to experience other problems, like any little itty bitty jitter in the machine is magnified.
The focal length on mine can be adjusted by turning the lens cap, so it is obviously more than a lens cap.
IIRC the most intense spot of the beam should actually be about 1/3 the thickness of the material below the surface, not right at the surface. The reason is that there is enough heat concentration to cut but some of the beam divergence is split between upper and lower surfaces. This may have changed over the years or is only applicable to Co2 lasers.