Runout is defined as the deviation from true rotation of a rotating part relative to the spindle or measurement instrument.

• A. The deviation from a straight path of the workpiece
• B. The amount of run time of the machine
• C. The deviation from true rotation of a rotating part relative to the spindle or measurement instrument
• D. The difference between spindle speed and feed rate

Answer: (C)

Runout measures how far a rotating part’s motion deviates from true rotation about the spindle axis. In a perfect setup, the part would spin with a constant radius around that axis. When runout is present, the axis of rotation isn’t perfectly aligned or the part is eccentric, so the actual path twists or wobbles as it turns. This is why the idea described fits best: it captures the deviation of the rotating part from true rotation relative to the spindle or a measuring instrument. You measure it with a dial indicator or similar tool, and you can have radial runout (side-to-side deviation) or axial runout (along the axis). Excessive runout leads to variable cutting depth, poorer surface finish, and dimensional errors. The other options describe different concepts (path straightness, machine runtime, or spindle speed versus feed rate) and don’t define runout.