Runout

Runout is the deviation of a rotating feature (spindle, cutting tool, or machined journal) from perfect circular motion around its axis, and excessive spindle runout degrades surface finish, hole accuracy, and tool life significantly. Machine spindle runout is typically measured in thousandths of an inch (TIR, total indicated runout), with precision spindles maintaining runout under 0.001 inches and ultra-precision machines under 0.0005 inches.

In turning operations, runout of machined features such as shaft journals is controlled by GD&T symbols like total runout, ensuring that bearings and mating parts seat correctly. Programmers minimize runout through careful work holding (using collets or chucks to grip the workpiece concentric to the spindle axis) and by performing machining operations that establish datums early in the sequence.

Regular spindle maintenance and tool holder cleaning help preserve spindle runout specification and ensure consistent precision throughout the life of the machine.