Stop Messing with "Old School" Tolerancing
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 next month's Tip.
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