View source for Run-out

{{Short description|Mechanical deviation from the intended axis}}
{{Use British English |date=May 2017}}
{{otheruses|Runout (disambiguation)}}

[[File:Radial Axial Runout.png|thumb|{{legend-line|red solid 2px|Top: Radial runout}}{{legend-line|#43b443 solid 2px|Bottom: Axial runout}}{{legend-line|black dotted 2px|Main axis}}]]
[[File:GD&T Circular runout.svg|thumb|right|[[Geometric dimensioning and tolerancing|Technical symbol]] for run-out]]

'''Run-out''' or '''runout''' is an inaccuracy of [[rotation|rotating]] mechanical systems, specifically that the tool or shaft does not rotate exactly [[rotation around a fixed axis|in line with the main axis]]. For example; when [[drill]]ing, run-out will result in a larger hole than the drill's nominal diameter due to the drill 
being rotated [[wikt:eccentric#Adjective|eccentrically]] (off axis instead of in line). In the case of [[bearing (mechanical)|bearings]], run-out will cause vibration of the machine and increased loads on the bearings.<ref>{{Cite web|url=https://www.emachineshop.com/gdt-runout-definition/|title=GD&T Runout Definition &#124; eMachineShop,com}}</ref>

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.

Absolute alignment is impossible; [[Accuracy and precision|a degree of error will always be present.]]

== Types ==
Run-out has two main forms:<ref>{{Cite web|url=https://www.reliableplant.com/Read/31021/measure-bearing-run-out|title=Why and How You Should Measure Bearing Run-out|website=www.reliableplant.com|language=en|access-date=2019-01-07}}</ref>

* ''Radial run-out'' is caused by the tool being translated off the machine axis, still parallel. Radial run-out will measure the same all along the machine axis.
* ''[[Rotation around a fixed 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.

Run-out 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.

===Radial run-out===
Radial run-out is the result of a rotating component running off centre, such as a ball bearing with an offset centre. This means that the rotating tool or shaft, instead of being centrally aligned, will rotate about a secondary axis. In general, cutting tools are more tolerant of radial run-out since the edges are parallel to the line of cutting tending to keep the tool tip aligned. However, a rotating shaft may be less tolerant of radial run-out since the centre of gravity is displaced by the amount of run-out.

===Axial run-out===
Axial run-out is the result of a rotating component not being parallel with the axis, such as a drill chuck not holding the drill exactly in line with the axis. In general, cutting tools are less tolerant of axial run-out since the tool tip tends to dig in and further increase run-out. However, a shaft may be more tolerant of axial run-out since the centre of gravity is displaced less.

==Measurement==
Typically run-out is measured using a [[Indicator (distance amplifying instrument)|dial indicator]] pressed against the rotating component while it is turned. [[Full indicator movement]] (previously called total indicator reading or total indicated run-out, TIR) is a term for the measured run-out of any rotating system, including all forms of run-out, at the measured point.<ref>{{Cite web|url=https://www.emachineshop.com/gdt-total-runout-definition/|title=Total Runout Tolerance &#124; eMachineShop.com}}</ref>

==See also==
* [[Chaotic rotation]]
* [[Geometric dimensioning and tolerancing]]
* [[Nutation]]
* [[Tire balance]], related concept in vehicles

==References==
{{reflist}}

{{Metalworking navbox|machopen}}

[[Category:Mechanical engineering]]