hi tweakie and thanks for ur graph
that shows non linear relation with P and i, in other pages i've found that power and feed have not linear relation for cut a certain width of materials
in other hand mach changes DC of pwm linear to feed rate, so this can explain the problem.
to overcome that i should do an internal table (in micro memory) to translate DC, which may this table be vary for different materials, so long project!!
i'll do that, as soon as i have enaugh time.
but this days i have some orders and busy , also have very bad EMI interference caused by laser tube
some times when triggering laser , computer or microcontrollers crashes. obviously caused by elecromagnetic field of spark in tube
i've grounded all electronics in single earth point, metal case for micros and drivers wich the case is grounded too, also laser power supply case and computer case
i finally think about wrapping tube in some aluminum foils   or even dig another earth hole in the yard especial for laser psu
did u have those problems too?

Hi bdn,

Fortunately, I have not had any problem with EMI radiation but my tube is mounted within an aluminum faced enclosure which is grounded to the machine frame and in turn bonded to Earth.

I am not sure that wrapping the tube with foil would be such a good idea but it would be nice to see some pictures of your setup / layout etc.

Tweakie.