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Stop Messing with Old School Tolerancing
(In accordance with Y14.5M-1994 standard)

PDF of this Tip

A recurring question I receive is: Do all toleranced dimensions relate to the datums stated on the drawing? And the answer is a resounding NO. Datums only apply when referenced. This drawing has multiple interpretations. Adding the note: DIMENSIONS RELATE TO DATUM A PRIMARY, DATUM B SECONDARY AND DATUM C TERTIARY (para 4.4 of ASME Y14.5M-1994) would help. However, there would still be many problems. Imagine trying to measure the 30mm radius and find its center. There isn’t an inspection machine in the world that could reproducibly return the "correct" answer. These problems are resolved in the June 2004 Tip.

Back to Tips Tip added May 2004