I spent the day yesterday getting the spindle back in balance, at least as perfect as I can get it, I was getting the vibration pattern in the finish cuts again, I havent machined anything yet but the spindle is smooth at 5140. There is no sheetmetal vibration now, just a bit of a whirring sound from the fenner belt. I have a spindle lockout on the machine now so this spindle nut- PDB problem shouldnt happen again.