GD&T Runout Definition
In GD&T, runout tolerance
is used to control the location of a circular part feature
relative to its axis
. This is different than circularity
, which controls overall roundness. Runout is usually applied to parts with circular cross sections that must be assembled like drill bits, segmented shafts, or machine tool components. Runout helps to limit the axis offset of two parts to ensure they can spin and wear evenly.
An example of runout tolerance is shown below. In the top figure the runout symbol is applied to the angled surface. The boxed symbols can be read "each circular element of this surface must have full indicator movement (FIM) of less than 0.1 relative to datum A". The bottom figure shows a sample measurement taken at one cross section, but multiple measurements are required to verify runout. Note that the indicator is applied perpendicular to the measured surface, and that this tolerance controls only individual circular elements and not the whole surface simultaneously (see total runout).