You might want to consider what I'm doing - using a stepper motor and high ratio planetary gear reducer to make an uber-power drawbar "wrench". With a 400 oz-in NEMA34 stepper motor mated to a 50:1 NEMA23 gearbox, I can *easily* generate well over 50 ft-lbs of torque on the drawbar, FAR exceeding the max tightening requirement (about 25 ft-lb), while having plenty of excess torque to loosen it. I use switchable current limiting resistors on the stepper driver to provide reduced torque when tightening, and full torque when loosening. By putting an encoder on the stepper, I can tell when the drawbar is moving, and when it's not, allowing me to back off a single turn for TTS tools, or fully undo the collet to swap in an R8 tool. No belleville washers needed, and no significant force on the spindle, as the only downforce we need is enough to pop the collet free (200-300 pounds max).