What is Total Runout in GD&T?
Similar to Circular runout, Total Runout tolerance in GD&T is used to control the variation in a feature when the part is rotated 360° about the datum axis. It is different from cylindricity because cylindricity calculates the roundness of any feature irrespective of any datum. Whereas total-runout determines the offset in the axis of a cylindrical feature with respect to datum feature. Don’t Miss this article on the basics of “Geometric Dimension and Tolerance”.
Representation in Engineering Drawing
Total-runout tolerance can be applied to only cylindrical features with respect to the datum surface or an axis. LMC and MMC modifiers are not used with total runout tolerance.
Total-Runout tolerance creates a 3 dimensional cylindrical tolerance zone. All points of the controlled surface must lie within two cylindrical surfaces (at a distance equal to tolerance value) when the part is rotated about the datum feature.
According to defined datums, Total Runout in GD&T controls the Circular runout, concentricity, cylindricity, circularity, straightness and perpendicularity of a round feature. It is generally defined in large transmission shafts, complex rotating assemblies etc. Since total runout controls so many tolerances, It is only defined in parts that need to be highly precise. Wherever possible, use of circular runout is more preferred.
How to Measure Total Runout?
Similar to runout tolerance, Total Runout can be measured using height gauge, surface plate and part rotating arrangement such as v-block or rotating chuck. To measure runout, firstly part is fixed at the datum points and dial gauge is fixed to the highest point on the controlled surface.
Afterwards part is rotated about the datum axis and dial gauge is moved along the complete length of the controlled surface. Total variation in the controlled surface should not be more than the given tolerance for the defined feature.