Does it vibrate without the nut?
I guess I would also try it with the nut but no collet.
I wonder if you can put in a large diameter drill rod and remove a little material from the perimeter. You could then rotate it relative to the nut and find the best clocking.
Yes. The other option might be to add a little aluminum tape to what you think is the light side and see if you are right.
One question that has no relevance to the balancing of the collet holder, but struck me as curious, why such high RPM's? Engraving? Soft materials? Micro cutters? Latest Gen of high speed, production, CNC mills?Always wanting to learn more,M