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I frequently hear people complain
that if MMC is used, they will have to build a dedicated gage
for inspection. Others believe MMC is only appropriate when
dealing with high volumes of parts. Both of these assumptions
are false. When MMC and LMC are applied to a geometric
tolerance, the control becomes a single limit that may not be
violated. On the part below, the straightness at MMC control
requires that the part not violate a boundary equal to the MMC
size of 24.8mm plus the straightness of 2mm which establishes
a boundary of 26.8mm.
To verify this, a simple
built-up gage may be used as a go/no-go inspection. Where
variable data is desired, an indicator may be zeroed out at
26.8mm. All readings, as the surface is trammed (probed), must
be below the zero point. In addition, of course, the size must
be verified with local measurements with a micrometer-type
device.
Note: The stock size and material usually are
stated in a material specification note. For that reason the
size appears here in parenthesis as a reference.
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