CIRCULARITY

DEFINITION

Circularity is a condition of a surface where :

  1. for a feature other than a sphere, all points of the surface intersected by any plane perpendicular to the axis are equidistant from that axis;

  2. for a sphere, all points of the surface intersected by any plane passing through a common center are equidistant from that center.

TOLERANCE ZONE

A circularity tolerance specifies a tolerance zone bounded by two concentric circles within which each circular element of the surface must lie, and applies independently at any plane.

REFERENCE TO DATUMS

Individual. No datum reference.

APPLICABILITY OF MMC, LMC, RFS TO FEATURE

Not applicable.

APPLICABILITY OF MMC, LMC, RFS TO DATUMS

Not applicable.

PERFECT FORM AT MMC

The circularity tolerance must be less than the size tolerance, except for parts subject to free state variation.

TYPICAL USE

Circularity tolerances are specified in cases when the function of the part necessitates that each circular element be round regardless of size or when size tolerances (rule #1) do not provide sufficent control of the roundness of the part. Also used to qualify a datum diameter.


NOTES :

  1. The circularity tolerance is a radial tolerance zone, not diametral.

  2. The circularity tolerance applies at each circular section of the diameter independently.

  3. Circularity tolerances can be applied to conical parts since individual circular sections must be round within tolerances.

  4. Circularity can be difficult to evaluate. When the surface has an evenly spaced odd number of lobes, point to point measurements cannot be used. Odd-lobbed parts usually appear perfectly round when measured with two point instruments (see ANSI B89.3.1).



SEE ALSO