Hi Mark just read ball the thread,very interesting I use a 650kv outrunnnermotor on a mill with a 80 amp speed controller, servo tester and a 15volt psu supplly. I have run it on mach3 to cut some small bearing pockets taking a 1mm cut with a 6mm cutter Ihave not had any problems with heat build up. I have fitted a fan on top of the speed controller bolted to the main frame of the mill.

Tony