Final answer:
Spindle speeds for lathe, mill, and drill press machines should be adjusted while the machines are OFF to ensure safety and prevent damage to the machine.
Step-by-step explanation:
Spindle speeds for lathe, mill, and drill press machines should be adjusted while the machines are OFF. It is important to ensure the safety of the operator and prevent damage to the machine. Making adjustments while the machines are off allows for proper calibration and reduces the risk of accidents.