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Think Boundary, not Bonus
(In accordance with Y14.5M-1994 standard)

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The typical approach to inspecting a feature such as the n1.000 hole is to measure the size, calculate a bonus and then try to locate the axis of the hole to see if it is within the allowable position tolerance. Another approach is to inspect the size and make measurements to see if the hole violates the inner boundary (virtual condition). If a hard gage were produced to inspect the position of this hole, it would have a pin n.970 (+gage tolerance and wear allowance) located at the basic location from the datums.

This hard gage may be simulated using a height gage in an open setup or CMM probe. By adding and subtracting half the virtual condition from the basic dimensions, the distance from the datums that may not be violated may be calculated. These distances may be easily inspected.

Back to Tips Tip added Mar 1999