Posted By on August 28, 2002 at 08:14:06:
In Reply to: True Position MMC posted byMaryAnn Clerici on August 26, 2002 at 14:33:35:
"When measuring hole to hole position with a MMC callout, which hole diameter dimension do you use for the bonus tolerance if the holes are at different MMC?"
I'm not sure exactly what your asking but, I'll try for an answer.
Basic dimensions (the dimensions with a rectangle around them) locate the hole feature relative the the Datum's. For a given hole pattern, with a given position tolerance at MMC, each hole is dimensionally (basic) defined back to the datum's. Each hole should meet the position tolerance requirements set forth within the feature control frame by itself. So, for each hole measured, one must calculate the allowable position tolerance (relative to the datum's) and determine if that hole feature meets the tolerance requirements. The allowed position tolerance for each hole within a pattern will vary as determined by calculating the "bonus" tolerance allowed by the divergence of the size tolerance of each particular hole. Sometimes, basic dimensions are "chained" from hole to hole feature. Still, one must determine the allowed tolerance relative to the indicated datums by doing the neccesary math to determine the actual distance the feature is allowed to vary from the datum's. Hole to hole tolerance is included within the defined position tolerance in the feature control frame for a particular pattern.
Hope this helps!
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