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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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