Hold down clamps, what do you use?

[Jonathan]

you don't need a lot of force to hold down the board, which means less warp upwards in the middle of the board.

Hence I just use double sided tape for PCBs. No distortion as well, no force really...
You could drill a 4mm hole somewhere convenient in or near the spindle mount and put a 4mm 'banana plug' on the wire. Annoyingly that method doesn't work for me since. presumably, the oil in the spindle bearings is electrically insulating the tool so I have to clip directly to the tool.