That answer makes me wonder - given that ballscrews have such low friction and a lead that means that a carriage could drive the screw, what happens to the Z axis when the power goes off the stepper and it loses almost all holding torque? With a heavy spindle plus Z mounting plate, etc., I could imagine the spindle dropping under its own weight. Does this happen in practice? Or does, say, a 1605 ballscrew in conjunction with the permanent magnetism in the stepper manage to stay put when power goes off?

Just curious!