Total runout is a GD&T control that limits the full indicator movement over an entire surface while the part rotates on a datum axis and the indicator travels along (or across) the surface. One reading covers roundness, straightness, taper, bend and off-centre error, which makes it the strictest runout control.
Where circular runout resets the indicator at each section, total runout does not. The indicator moves along the full length of the diameter (or across the full face) while the part turns, and the highest-minus-lowest reading over the whole sweep must be within the tolerance.
On a diameter, that one number controls cylindricity and location of the surface relative to the axis. On a face perpendicular to the axis, it controls flatness and squareness of the face to the axis together.
It is specified on bearing seats, seal surfaces along their full width, rotor faces and shafts that must slide through a bore.
For a diameter: two coaxial cylinders, centred on the datum axis, the tolerance apart radially. For a face: two parallel planes perpendicular to the datum axis, the tolerance apart.
Unlike cylindricity, the cylinders cannot float: they are locked to the datum axis.
Total runout always needs a datum axis, often a common axis from two bearing journals (A-B), or a face plus a diameter.
| Modifier | With total runout |
|---|---|
| MMC or LMC | Not allowed. Total runout is always RFS, and datum references are at RMB. |
| Diameter symbol | Not used. The value is a full indicator movement. |
Example: a Ø40 mm bearing seat, 30 mm long, total runout 0.05 mm to datum axis A-B
Result: 0.043 ≤ 0.05, so the seat passes. Circular runout at each section was only about 0.02; the rest is taper.
Every GD&T symbol page: GD&T symbols chart
Yes. With the same value, a part that passes total runout always passes circular runout, but not the other way round.
Yes. Every point of the surface must be inside two coaxial cylinders on the datum axis, so form and location are both limited.
Yes. On a face perpendicular to the axis it controls flatness and perpendicularity to the axis together.
Yes, always a datum axis.
Rotate the part on its datum features while moving an indicator along the full surface on a slide parallel to the axis, and take the full range of readings.
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