{"id":9894,"date":"2021-04-19T17:25:08","date_gmt":"2021-04-19T14:25:08","guid":{"rendered":"https:\/\/fractory.com\/?p=9894"},"modified":"2024-01-26T14:55:53","modified_gmt":"2024-01-26T12:55:53","slug":"circularity-gdt-explained","status":"publish","type":"post","link":"https:\/\/fractory.com\/circularity-gdt-explained\/","title":{"rendered":"Circularity (GD&T) Explained"},"content":{"rendered":"

The geometric dimensioning and tolerancing (GD&T) standards in ASME Y14.5-2018<\/a> define five main types of controls for various part features. These are form, location, orientation, profile and runout. The form control in GD&T controls the form of individual part features.<\/p>\n

Circularity belongs to the form control group. It controls the geometry of circular features such as cones, cylinders and spheres.<\/p>\n

In this article, we shall learn about the circularity callout and how we can use it to ensure the final part’s maximum closeness to its intended design.<\/p>\n

What is Circularity?<\/h2>\n

The geometrical tolerance of circularity is one of the four types of form control, the others being straightness<\/a>, flatness<\/a>\u00a0and cylindricity. Also known as roundness, it control\u2019s a feature\u2019s circular nature such as the diameter of a cylindrical pin or a hole.<\/p>\n

The aim is to set a limit to the desired accuracy of the circular feature in relation to a perfect circle<\/strong>.<\/p>\n

Circularity Tolerance Zone<\/h2>\n

The circularity callout defines a two-dimensional tolerance zone for the actual part surface. The tolerance zone consists of two concentric circles that lie on a plane that is perpendicular to the central axis of the part feature.<\/p>\n

\"Circularity
The circle’s measurements must lie within the blue zone<\/figcaption><\/figure>\n

The difference between the radii of these two circles defines the permissible tolerance limit for the feature.<\/p>\n

To understand it better, one may imagine an infinite number of tolerance zones in contact with one another to cover the entire surface (like discs in a stack). All the zones may not be of the same size (as in the case of a cone).<\/p>\n

For part approval, all the points on a circular feature\u2019s cross-section must lie in their respective tolerance zone, i.e. between the two circles. Thus, a sequence of circular tolerances can be used to determine the conformity to requirements of various cross-sections.<\/p>\n

Circularity vs Other Callouts<\/h2>\n

Circularity may sometimes be confused with other callouts. Each callout has a specific function and a method of measurement.<\/p>\n

A designer chooses the right callout for an application after considering various factors such as the degree of accuracy, tolerance limit, and ease of measurement. The following information will help us understand the difference between the different radial callouts in geometric dimensioning and tolerancing<\/a>, and in making wiser choices regarding the same.<\/p>\n

Circularity vs cylindricity<\/h3>\n

Cylindricity is the 3D counterpart of circularity<\/strong>. While the latter concerns itself with only the roundness of the feature, the former also controls the straightness of the circular feature\u2019s central axis<\/strong>.<\/p>\n

Cylindricity tries to bring the feature\u2019s form as close as possible to a perfect cylinder.<\/p>\n

Designers use cylindricity when, in addition to the diametral tolerance, the feature\u2019s straightness plays an important role in the part assembly. For instance, a pin may have the diametral variation well within limits, but if it isn\u2019t straight enough, it will not fit the hole.<\/p>\n

Cylindricity is also different from circularity in that it is meant for features with a constant diameter, thus not suitable for conical shapes, for example.<\/p>\n

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