CIRCULAR RUNOUT

RUNOUT

Controls surface variation at each circular cross-section

⚠ DATUM REQUIREDASME Y14.5-2018 §12.7

Circular runout controls the variation of a surface as measured at individual circular cross-sections when the part is rotated about a datum axis. A dial indicator measures the total indicator movement (TIM) at each cross-section. It combines circularity and coaxiality at each slice independently.

WHEN TO USE IT

Use circular runout on rotating parts — shafts, bearing journals, pulley surfaces, and similar features — where the surface must not wobble or oscillate at any individual cross-section during rotation. It is easier to measure than concentricity and more directly tied to functional performance.

COMMON MISTAKES

Omitting the datum axis reference — runout always requires a datum

Confusing circular runout with total runout — circular runout measures one cross-section at a time, total runout measures the full surface simultaneously

Applying runout to non-rotating or non-cylindrical features where it is not appropriate

Using runout when position or concentricity is actually the intent