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Rules for Composite Position Tolerancing

Composite Position Tolerancing is a confusing topic. Y14.5M-1994 dedicates about 35 pages to explain it. In this webtip I have condensed the Y14.5 description into a set of Rules for Composite Tolerancing. The nine rules can help to determine if a composite position control is properly specified or is being properly interpreted. The Rules are extracted from Advanced Concepts of GD&T, By Alex Krulikowski.

1. The Pattern Rule.
A composite position control must be applied to a set of multiples features of size. (i.e. a pattern of holes, coaxial diameters, etc.)
2. The Segment Rule.
A composite position control can only contain two segments. (the PLTZF and the FRTZF).
3. The Upper Segment Rule.
The upper segment can and must control the location and/or orientation of the pattern.
4. The Lower Segment Rule.
The lower segment can and must only control the spacing and/or orientation of the pattern.
5. The Tolerance Refinement Rule.
The tolerance value of the lower segment must always be a refinement of the tolerance value of the upper segment.
6. The Basic Dimension Rule.
Basic dimensions (specified or derived) that define location of toleranced features apply to the upper segment only. Basic dimensions (specified or derived) that define spacing and/or orientation apply to both segments.
7. The Datum References Rule.
Any datum references and datum modifiers in the lower segment must be repeats and in the same order of the datum references and datum modifiers of the upper segment.
8. The Segment Verification Rule.
Each segment of a composite position control must be verified separately.
9. The Separate Requirement Rule.
The simultaneous requirement default does not apply to the lower segment of composite position controls.
 

 



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This file last modified 01/08/09