I think you are on the right track thinking that the mill is tripping the arc fault breakers. The mills made for US consumption do not have any internal noise filtering and this means that pulses from the PWM controller in th e mill back up into the power line. This is why I recommend short fat AC supply lines from the mill to the panel. In this case it seems to have backfired since the pulses are affecting everything else.
See if you can get a hold of a motor run capacitor (NOT a start capacitor) and place it across the hot/neutral wires going to your mill. It should act as a filter to reduce noise backing up into your power line.
I suspect you are some distance from the utility transformer (pole pig) and this inductance is aggravating the problem.
I use 4 - 600 volt oil filled capacitors in parallel across the output of my isolation transformer to prevent spikes from damaging/causing problems with other devices across the power line. Before I installed them I was occasionally blowing up MOV's - Varistors on the mill circuit boards.
-Pete
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