When operating a lathe, where should the tool bit typically be positioned?

• A. Above center to obtain better surface finish
• B. Below center to enhance chip evacuation
• C. Directly on the spindle centerline
• D. None of the above

Answer: (C)

Position the tool so that its tip sits on the workpiece axis. When the tool is on the centerline, the cutting edge engages evenly as the work rotates, producing a true radial cut with forces that are balanced and directed into the work. This gives a clean surface finish, accurate dimensions, and stable cutting with less tool deflection and chatter.

If the tool sits above the centerline, it tends to rub the surface before cutting begins, leading to poor finish and potential chatter. If it sits below the centerline, the edge can dig in and create higher thrust, more wear, and rougher finishes. Therefore, aligning the tool on the spindle centerline is the standard setup for typical turning operations.