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Unlock Composite Tolerancing, Part II of III
(In accordance with the ASME Y14.5-2009 standard)

PDF of this Tip

In part 1 of this 3 Tip series you saw how a composite tolerance may be used to control the relationship of features within a pattern.  The lower segment, in that case, was used to tie the two holes together to act as one. In this Tip there is an additional segment added to the middle of the composite position tolerance and reference to datum feature A is repeated.  Some people incorrectly think that this segment tightens the location of the holes relative to the datum plane established by datum feature A.  The rule is that datum feature references in lower segments of a composite tolerance refine orientation only.

So, in this case, based on the upper segment, the holes can float around 0.4 mm, if produced at MMC, relative to the datums established by datum features A and B. Based on the second segment the pattern of holes may not be out of parallel to the first datum plane by more than 0.25 mm if produced at MMC. And, based on the lowest segment, the holes must be in line (coaxial) within 0 mm if produced at MMC. The parallelism of the pattern of two holes relative to the second datum plane (the one established by datum feature B) is controlled by the location tolerance of 0.4 mm.

The last Tip in this series will show how to better control the parallelism to the second datum plane by adding another segment to the composite position tolerance. Be sure to watch the video of this Tip to see animations of these tolerance zones.

Back to Tips Tip added May 2012