That can also be a byproduct of feeding to slow as you get melt and fusing at the top of the piece being cut. Just something that came to mind as I was cutting and cleaning up a new jig for the machine. When doing finishing surface profile with a 6 mm 2 flue I am normally running at 2.25 m/min or slightly faster (up to 3m/min on really thin finish passes) and that leaves a very nice smooth finish that polishes easily if needed.

Michael