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Sometimes Profile of a Line Turns into Profile of a Surface, when Datum References Are Used
(In accordance with Y14.5M-1994 standard)

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Profile of a line is a funny control. It works well for parts like extrusions where individual slices will be checked. However, when you start adding datum references, it can turn into a profile of a surface control.

The first drawing uses a profile of a surface tolerance to locate the surface. This tolerance is refined by a profile of a line tolerance. The profile of a line tolerance floats within the profile of a surface tolerance zone and applies to individual slices of the surfaces. This is fine if that is what the design intent of the part is.

On the second drawing datum references have been added to the profile of a line tolerance. The result is that the profile of a line tolerance overrides the profile of a surface tolerance. Since every line in the surface must be located with respect to the datums, the entire surface is being controlled for location by the profile of a line tolerance. The profile of a surface tolerance is meaningless.

Back to Tips Tip added Jan 2006