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Last
month's Tip showed that when MMC and LMC are applied to a
geometric tolerance the control becomes a single limit that
may not be violated. Once that is understood, inspection and
the collection of data may become much easier. For the two
holes on the drawing shown, once the size is measured and the
datum planes established, the CMM (coordinate measuring
machine) probe may be moved to the basic location of each
hole. From there, polar measurements may be made to assure
that the surface of the hole does not violate the inner
boundary. This inner boundary is all that needs to be checked
to verify the position tolerance on the holes. In this case,
the inner boundary is 10 - 0.1 - 0.6 = 9.3. This value is the
hole's virtual condition. It is also the theoretical design
size of a gage pin that would be found in a receiver-type gage
if one were built. In other words, the surface of the hole may
not be closer to the basic location than 4.65mm which is the
radius of the inner boundary. There is no need to find the
axis of the hole and determine if it meets the position
tolerance.
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