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All Geometric Tolerances Are Total (#282)

(In accordance with the ASME Y14.5-2009 standard)

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The default of all geometric tolerances is a total wide tolerance zone. If you want a different shaped tolerance zone, you have to say so. The most common is the cylindrical tolerance zone which is indicated by placing the Ø symbol in front of the tolerance value. Where a spherical tolerance zone is required, SØ is applied. Other tolerance zone shapes may be indicated by the placement of the feature control frame.

Here the 4 holes have two position tolerances applied. They define a radial tolerance zone of 0.1 with a length of 0.4.

The spherical part below illustrates a spherical tolerance zone. Notice the SØ included in the position feature control frame. The perpendicularity tolerance does not have anything preceding the tolerance value. Therefore, the tolerance zone defaults to a total width.

In the early days of GD&T, TOT was used to indicate total. DIA for diameter and R for radius were also used. However, if one of these was omitted it wasn’t clear what size or shape the tolerance zone should be. Bottom line, be sure to indicate if you do not want a simple width as a tolerance zone.

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Back to Tips Tip added Jul 2013