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Circularity (Roundness) Tolerance

Circularity (Roundness) describes the condition on the surface of revolution (cylinder, cone, sphere), where all points of the surface intersected by any plane perpendicular to a common axis (cylinder, cone); or passing through a common centre (sphere) are equidistant from the centre.
 
Circularity (Roundness) refers to a condition of a circular line or the surface of a circular feature where all points on the line or on the circumference of a plane cross section of the feature are at the same distance from a common axis or centre point. It is similar to the straightness geometric control except that it is wrapped around a circular cross section.
 
The tolerance range in the considered plane is the area between two concentric circles separated by distance t.
 
The circumference in any section normal to the axis shall be contained between two concentric circles separated by 0.1mm on the same plane.
 
Cylindrical features can have three different form characteristics:
  • Straightness
  • Circularity or Roundness
  • Cylindricity
Circularity defines how much circular elements can vary from a perfect circle. The circularity control, like other form controls, is used to define the shape of a feature in relation to itself; therefore, it never uses a datum reference. 
 
Circularity or Roundness is a condition where a feature is a continuous curved surface, and any point of its surface is at a constant distance from its common centre or axis. In other words, circularity is a condition of a surface where:
  • For a feature other than a sphere, all points of the surface intersected by any plane perpendicular to an axis are equidistant to that axis
  • For a sphere, all points of the surface intersected by the plane passing through a common centre are equidistant from that centre

 

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