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Sometimes Profile of a Line Turns into Profile of a Surface,
when Datum References Are Used
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.
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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. |
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