Hie I have a chinese k40 40watt machine and I want to cut 1mm dots but it leaves burns on the edges and whe I increase speed it cuts randomly.
Have got the power as low as possible? Have you got air assist?
Same with mine put the speed at 400mm/s with very low power also try putting a masking tape under and over the area you want to cut it pics up most of the ash.
When you set the speed that fast, the servo’s cannot keep up with where the software thinks the laser is positioned.
If you continue having problems, there is a very active facebook group helping with hardware and software problems on the laser. Laser cutting and engraving https://www.facebook.com/groups/441613082637047/