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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