Originally Posted by
tommylight
That statement in the original post is not correct.
Pilot arc is ANY plasma that has the means to strike an arc without physical touch, so that include HV AND HV/HF start plasmas.
Scratch start and blow back do not have a pilot arc so they have to make physical contact with the material. That makes them not suitable for use on CNC machines.
As for interference, that HV/HF type does create much more interference, but they can and are used on cnc machines, and so are the HV start ones.
Back to your problem,
You need to have the proper grounding and shielding, otherwise nothing will help you. A metal case for the electronics is a must, separating the cnc machine from the cutting table is also good to avoid interference if you do not have proper grounding.