Which parameter should be adjusted with the mills, lathes, and drill presses running?

• A. Spindle Speed
• B. Feed Rate
• C. Depth of Cut
• D. Torque

Answer: (A)

Maintaining proper cutting speed at the tool tip is what governs how a cut proceeds. Spindle speed directly controls how fast the tool and workpiece rotate, and that rotation rate determines the cutting speed for the material and tool in use. As you machine, keeping this speed within the recommended range helps manage heat, tool wear, and surface finish. You can and should adjust this parameter during operation to compensate for changes in tool diameter or material, so the cutting conditions stay efficient and safe.

Changing feed rate or depth of cut while the tool is engaged increases cutting forces, which can cause tool deflection, chatter, poor surface finish, or even breakage. Those settings are typically adjusted with the tool either retracted or the machine stopped, to avoid loading the tool or compromising safety. Torque is largely a result of the load on the spindle and the motor response; it isn’t a direct knob you routinely dial in while cutting. This is why spindle speed is the parameter that’s practically adjusted while the mills, lathes, and drill presses are running.