What are radial and axial runout error?

Runout is the inaccuracy in a rotating mechanism where rotation does not occur around the main axis.

• Radial runout is when the axis of rotation is off-center from the main axis, but still parallel.
• Axial runout is when the axis of rotation is tilted to some degree from the main axis, meaning the axis of rotation is no longer parallel to the main axis.

Concentricity error can cause the rotor to have runout. Axial runout can be motor-driven, as there are some small forces that push and pull the rotor up and down axially. These forces are typically minimized during the design phase and constrained by bearings. Air bearing systems may see this effect because they are not as stiff as mechanical systems.

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