Cutting carbon steel? A smaller nozzle would be a great start. You will pierce cleaner. Also pierce all of the holes first and then go back and cut them. 2400W .05-.06 Mpa. Also pulsing can help. Try about 3500W, 400 hertz, 70 Duty
We have found that a mirror can look perfectly clean and have coating that is failing. If you clean a reflector and there are tiny gold specs on the lens paper, the coating has failed.
Pre-pierce. I find that this solves most of the problems with small holes. Also, pulse with 400-500 Hertz and about 65 duty. By combining these two strategies we once cut 11/32 holes in 3/4 plate for about three hours with a 6K PRC.
