Many believe that
when MMC is applied to a geometric tolerance, hard
gaging, must be used. Hard gaging does not provide
variable data and therefore is often not desirable for
process control. Also, many customers today require that
production calculate the Cpk of the process. The
application of MMC or LMC may be thought of as
specifying a single limit for
position. |
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This drawing, for
example, only requires that the size and inner boundary
(virtual condition) of the hole be verified. The virtual
condition is a single limit requirement. The theoretical
design size of the gage pin (1) is 8.0-0.2=7.8. The
distance from the axis of the datum simulator to the
surface of the gage (2) is 3.9 (7.8/2).
By using
an indicator, which is mastered at 3.9 from the datum
simulator, variable data may be collected. Recording the
distribution of data relative to the inner boundary
allows the calculation of Cpk of the process. |