Which of the following is NOT among the three things you should check before/when turning on milling machines?

• A. Tool clearance
• B. Speed range
• C. Rotation direction
• D. Coolant type

Answer: (D)

When you power up a milling machine, the essential checks focus on safe setup and preventing tool crashes: you verify that the tool has enough clearance from the workpiece and fixtures, confirm the spindle speed is appropriate for the tool and material, and make sure the spindle will rotate in the correct direction for the intended operation. These checks directly affect whether the machine will cut safely and effectively as soon as it starts.

The coolant type isn’t something you typically decide or verify at the moment of turning on the machine. You may ensure coolant flow and availability so cooling and lubrication happen during cutting, but the specific coolant type is chosen based on the material and tooling needs and isn’t a startup parameter. That’s why coolant type isn’t among the three checks.