On a lathe, where should the tool bit be positioned for normal cutting?

• A. Above center to obtain better surface finish
• B. Below center to optimize chip evacuation
• C. Directly on the spindle centerline
• D. Wherever it happens to be

Answer: (C)

Position the tool so that the cutting edge sits exactly on the centerline of the workpiece. This places the edge at the same height as the axis of rotation, yielding balanced cutting forces and a clean shearing action as the work spins. If the tool is above the centerline, it tends to rub and scrape, leading to a poorer surface finish and increased tool wear. If it’s below the centerline, the edge engages more shallowly and can cause chatter and an uneven cut. Directly on the spindle centerline provides the best combination of surface finish, control, and tool life for normal turning cuts.