Total Runout Tolerance: Specify It Right on CNC Shafts

Total runout tolerance is a GD&T control that limits variation across an entire surface as the part rotates 360° about a datum axis. Apply it to CNC turned shafts, bearing journals, seal seats, and spigots where radial and axial errors both matter. It is stronger than circular runout because it checks the full surface, not one cross-section.

The specification only works if the datum is functional. Call out the bearing journal or centers as the datum, not a convenient face or chucking diameter. For a 303 or 304 stainless pump shaft, a 0.02 mm total runout callout to the bearing datum is realistic. Tightening to 0.005 mm may require hard turning, grinding, or a dedicated fixture, which adds cost and lead time.

Inspection method matters. A shop may verify between centers with an indicator; a CMM with a rotary table can map the surface. If the drawing is ambiguous, results can differ. State the datum, tolerance zone, and whether the feature is cylindrical or planar. For seal surfaces, pair total runout with Ra 0.8 micron or finer.

Match runout to function. General shafts often work at 0.05 mm. Precision rotating parts may need 0.01–0.02 mm. Spindle-grade 7075-T6 or steel justifies 0.005 mm only when the assembly requires it. A clear total runout callout prevents scrap, simplifies inspection, and keeps quotes comparable.

Need a machine shop that can hold these requirements? Explore our CNC machining services or request a quote for your part at CNCdoing.

For more guidance on related work, see: Tight Tolerance CNC Machining: Datum Strategy That Works.