GD&T Circularity Symbol (unexpected results)

Circularity is often described as the round version of straightness, in that it only measures a single cross section at a time.

Circularity specifies a circular TZ, or a TZ framed by two concentric circles. For instance, every cross section of this pin would need to fit inside the .3mm TZ.

However, there are two important limitations of circularity as a control. The first is that circularity measures how round something is, not what size it is. If a feature, like a pin, needs to be round to .08mm it can pass inspection at almost any size.

A straight pin could still have waves like this in it and meet tight circularity tolerances. This wide section is within a .08mm circularity TZ, and this narrow section is as well, thought the second TZ has a smaller diameter.

The second limitation is that circularity, as a form control, is measuring the roundness of a cross section, not in relation to anything else. This means your cylinder could have been terribly assembled like a stack of discs, and still pass inspection. Each cross section of this strange pin is circular to spec, even though this pin clearly does not look like the intended drawing.

Circularity can be useful for non-cylindrical parts that still need to be round. A cone or a handle for a garden tool would each have a series of cross sections that needed to be round, but not necessarily the same size.

A special use of circularity is calling out the circularity of a sphere, such as a ball bearing. In this case the cross-section plane spins around the center of the sphere and does not stay perpendicular to an axis. For each cross-section measured this way the surface points must fall within a circular TZ.

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[saurabhroy]

Give a practical example. like take a assembly of pin and hole and then show if we do not control the circularity then what will be problem... something like that....tons of simple demonstrate videos are present in YouTube.

[MrKadvaga]

Annoying pop-up links block the graphics towards the end of the video.