Position Tolerancing—Expanded Principles, Symmetry, and Concentricity
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Transcript of Position Tolerancing—Expanded Principles, Symmetry, and Concentricity
9Position Tolerancing—Expanded Principles,
Symmetry, and Concentricity
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• Explain functional gaging methods for checking hole position tolerances specified at MMC.
• Specify and explain composite position tolerance specifications.
• Explain the effect of using identical datum feature references in multiple position tolerance specifications.
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• Specify separate pattern requirements for groups of features not acting as a single pattern.
• Specify position tolerances for in-line holes.• Specify tolerances to control symmetry.• Control coaxial features with position or
concentricity tolerances, depending on the given application.
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Symmetry
• Position tolerance • Symmetry tolerance
– Symbol removed from standard in 1982– Symbol reinstated in 1994
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Position for Symmetryof Hole Patterns
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Symmetry for Features of Size
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Concentricity
• Requires derived median line located relative to datum axis
• Always has diameter symbol• Always applied RFS• Must have datum feature reference• Datum reference is always RMB• Rarely used
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Concentricity Feature Control Frame
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Concentricity Median Line
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Concentricity Zero Error
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• Even though a feature has surface and size variation, it may have no concentricity variation
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Composite Position Tolerance
• One position symbol• Two or more segments• Same datums, same order, same modifiers
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PLTZF
• Pattern-locating tolerance zone framework• Pronounced plotz• First segment• Located relative to datum reference frame
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FRTZF
• Feature-relating tolerance zone framework• Pronounced fritz• Lower segment(s)• Not located relative to datum reference frame• Constrained in rotation relative to referenced
datums• Must, at a minimum, overlap PLTZF
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Composite Position Application
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No Repeated Datum References
• Free to float relative to datum reference frame• Features must be able to meet tolerance
requirements in first and second segments
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Repeated Primary Datum Reference
• Rotational degrees of freedom constrained relative to primary datum
• Features must be able to meet tolerance requirements in first and second segments
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Repeated Primary and Secondary Datum Reference
• Rotational degrees of freedom constrained relative to primary and secondary datum
• Features must be able to meet tolerance requirements in first and second segments
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Functional Gaging for Position Tolerances at MMC
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Gaging a Composite Position Tolerance
• Similar to single segment position tolerance• Two gages typically required to check composite
tolerances