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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.

In addition, irregular run-out is the result of worn or rough bearings which can manifest itself as either axial or radial run-out.

Runout will be present in any rotating system and, depending on the system, the different forms may either combine increasing total runout, or cancel reducing total runout. At any point along a tool or shaft it is not possible to determine whether runout is axial or radial; only by measuring along the axis can they be differentiated.

Absolute alignment is not possible; a degree of error will always be present.

Usage examples of "run-out".

During the past week or so, strong winds and spring tidal conditions have made Haulover particularly treacherous, with invisible run-out currents sweeping many swimmers out toward the open water.

Jack followed him, jumping perilously on to the muzzle of a run-out carronade and so over what was left of the hammocks on to the American quarterdeck.