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You Don’t Always Need a Hard Gage
(In accordance with Y14.5M-1994 standard)

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The September 2003 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 4.65 mm 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.

Back to Tips Tip added Oct 2003