GD & T Characteristics - A-3 Circularity

A-3: Circularity : 

GD & T Characteristics  - Circularity  

Circular profiles corresponding to some external or internal diameters are required to be reasonably circular. The loss in circularity can disturb the motion of a follower when the revolving cam and reciprocating follower are at a "dwelling" state. Loss of circularity can disturb the amount of interlocking between the outer race of H ball bearing and the corresponding bore of a gearbox housing. Loss of circularity at the rolling wheels can disturb the smoothness of the straight-line motion of the carriage. 

The term circularity is applicable for circular Objects like thin rings or for even cylindrical objects with appreciably short widths.

A circularity tolerance symbol shall be a small circle Of a diameter I times the height of any alphabet or numerical figure at the feature control frame. The amount indicating the permissible deviation is at the second chamber of the feature control frame as usual. The feature control frame can be put in the front view, or inside View, or attached to the parent dimension in the front view. The permissible deviation at the circularity has to be smaller than the tolerance amount at the basic size. The permissible deviation indicates that the innermost and the outermost zone of the deviated profile must be within two concentric circles with the radial difference equal to the permissible deviation (i e., 0.015 mm in the shown case). Such circularity tolerance can be even for an internal diameter.

Fig.1. Circularity

Measurement / Gauging - 

The deviation at the circularity is seen to be generated during Flange turning, boring, cylindrical grinding, centerless grinding operations where the radial travel of the tool is predominant over the lateral travel. Hence, it is more relevant for diameters of short width. The deviated commonly appear like "lobe" (triangular) Shape s 'elliptical" Shaps rather than any general erratic shape. The deviations can be judged by fitting the circular component with its size counterpart and noticing the contacting zone. If the deviation is to be measured. then a dial indicator with a suitable least count is arranged against the circular profile. the component slowly revolved around its axis by one rotation and the dial readings noted for progressive rotations like 0°, 30°, 60°, 90° ….., 330°, 360°.

Fig.2. Circularity

However, their observations, if mixed with the errors regarding eccentricity of the axis, cannot be exactly correlated to the errors at circularity. An alternative of mounting the component over a Suitable 'V • block and noting the dial after revolving the component by 360° gradually, better results regarding circularity deviations. The Observations are Obtained over where the component gets in the 'V' block.

When Used : 

Circularity property is a common measurement and its uses during manufacturing. The part should be perfectly round for its functional purpose. 

For Example, rotating shaft, bearing, etc such kind of product must be considered its circularity property.

The circularity also called 'Out'. In the mechanical engineering drawings can see this GD & T symbol mostly.  

Relation to other GD & T symbols - 

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