I would have thought the first strep would be to drive the spindle from a completely separate power supply, that is completely separate......I get the impression from your characteristics that if you get a problem then address it at that particular event.......the spindle is obviously causing a power dip on your supply line, and that might be a factor of your power supply to the house.

We had this problem with our NC machines in Bristol UK in the 70's and it was caused by a large capstan lathe braking and throwing a spike on the line.....this was cured when the power company installed a new heavier transformer for the shop supply from the grid.
Ian.