Run-out
Run-out or runout is an inaccuracy of rotating mechanical systems, specifically that the tool or shaft does not rotate exactly in line with the main axis. For example; when drilling, run-out will result in a larger hole than the drill's nominal diameter due to the drill
being rotated eccentrically (off axis instead of in line). In the case of bearings, run-out will cause vibration of the machine and increased loads on the bearings.
Run-out is dynamic and cannot be compensated. If a rotating component, such as a drill chuck, does not hold the drill centrally, then as it rotates the rotating drill will turn about a secondary axis.
Run-out has two main forms:
Radial run-out is caused by the tool or component being rotated off centre, i.e. the tool or component axis does not correspond with the main axis. Radial run-out will measure the same all along the main axis.
Axial run-out is caused by the tool or component being at an angle to the axis. Axial run-out causes the tip of the tool (or shaft) to rotate off centre relative to the base. Axial run-out will vary according to how far from the base it is measured.