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Everywhere I go I find people who
think that the part must be inspected better when GD&T is
used. Although we talk about 100% inspection, it never really
happens. This example shows two ways to tolerance the
thickness of a block. How can anyone declare that because a
profile of a surface tolerance is used, the part must be
inspected more closely? The + tolerance requires making
certain that no two point measurements are less than .990. For
the profile of a surface, all points are to be within .010 of
the BASIC goal of 1.000. In both cases it would not be
practical to contact all points on the surface. Therefore,
enough points are checked to be confident the parts are good.
The more points checked, the greater the confidence. In other
words, it's work versus risk, regardless of how the
requirement is specified.
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