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Position Tolerancing—Expanded Principles, Symmetry, and Concentricity

9. Position Tolerancing—Expanded Principles, Symmetry, and Concentricity. Explain functional gaging methods for checking hole position tolerances specified at MMC. Specify and explain composite position tolerance specifications.

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Position Tolerancing—Expanded Principles, Symmetry, and Concentricity

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  1. 9 Position Tolerancing—Expanded Principles, Symmetry, and Concentricity

  2. 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.

  3. 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.

  4. Symmetry • Position tolerance • Symmetry tolerance • Symbol removed from standard in 1982 • Symbol reinstated in 1994

  5. Position for Symmetryof Hole Patterns

  6. Symmetry for Features of Size

  7. 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

  8. Concentricity Feature Control Frame

  9. Concentricity Median Line

  10. Concentricity Zero Error • Even though a feature has surface and size variation, it may have no concentricity variation

  11. Composite Position Tolerance • One position symbol • Two or more segments • Same datums, same order, same modifiers

  12. PLTZF • Pattern-locating tolerance zone framework • Pronounced plotz • First segment • Located relative to datum reference frame

  13. 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

  14. Composite Position Application

  15. 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

  16. 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

  17. 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

  18. Functional Gaging for Position Tolerances at MMC

  19. Gaging a Composite Position Tolerance • Similar to single segment position tolerance • Two gages typically required to check composite tolerances

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