I recently replaced the tube for my 40w laser and I have perfect cuts for the first 10 or so cuts. It was cutting through 3mm wood on 1 pass with less that 50% power. Now I can cut through 3mm no matter how many passes. I checked the mirror and cleaned everything. It appears the beam coming out of the tube has a larger diameter and it seems that the beam is broken into 4 points. This is a new development as when I was aligning the mirrors after replacing the tube I had a much tighter more powerful beam.
Now I am still learning so my assessment of the issue could be completely wrong. Thanks so much.