Yeah, I cut a few pieces today. The machine was singing. I played with RPMs to try to mitigate but there really doesn't seem to be a simple formula to make this happen without lots of chatter/vibration.
I have no experience with CNC plasma cutting. I did some looking around and learned of guys mounting an extension arm out the front/side of their VMC to plasma-cut outside the machine. Sounds wicked enough that I could see myself trying that one day (not for this).
What kind of tolerances can a real CNC plasma cutter hold? +/- 0.010" is probably fine for this job, maybe more.
plasma on most leave a 0.030" kerf. high def gets it to about 0.008"