Spindle speeds on the lathe, mill and drill press should be adjusted while the machines are OFF.

• A. True
• B. False
• C. Only when calibrating
• D. Not specified

Answer: (B)

The main idea here is safety when changing spindle speed. Changing the drive setup or speed control on lathes, mills, or drill presses involves interacting with moving parts and belt drives. If the machine is running, a speed change can cause a sudden start, belt slip, or contact with rotating components, which can lead to serious injury. Powering the machine down stops all motion, relaxes belt tension as needed, and prevents an unexpected start while you adjust the pulleys or the electronic speed setting. Once the machine is OFF, you can make the change, verify the new setting, and then start up again with guards in place and the workpiece secured. So, the recommended safety practice is to adjust spindle speeds only when the machine is OFF and secured.