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Position Tolerancing Fundamentals

8. Position Tolerancing Fundamentals. Complete feature control frames for position tolerances, properly using the diameter symbol, material condition modifiers, and datum references. Sketch the proper location and shape for position tolerance zones.

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Position Tolerancing Fundamentals

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  1. 8 Position Tolerancing Fundamentals

  2. Complete feature control frames for position tolerances, properly using the diameter symbol, material condition modifiers, and datum references. • Sketch the proper location and shape for position tolerance zones. • Describe the effect of an MMC, LMC, or RFS modifier on a position tolerance.

  3. Provide examples that prove the validity of the MMC concept as it applies to position tolerances. • Calculate position tolerances for simple fixed and floating fastener conditions. • Calculate the allowable bonus tolerance for a produced part on which a position tolerance is specified at MMC.

  4. Position Tolerances • May be used on single or multiple features • Tolerance zone shape determined by functional requirements for feature • Material condition modifiers are appropriate

  5. Feature Control Frame

  6. Material Condition Modifier Application

  7. Basic Dimensions • Must be used to define location when position tolerances are applied to features • Defines true position

  8. Effect of RFS

  9. Effect of MMC

  10. Proof of MMC Concept

  11. Floating Fastener Condition • Fastener passes through multiple clearance holes • Common to use same size clearance holes for all parts, but not required

  12. Floating Fastener Tolerance Calculation Hole = .328.004 Fastener = .312 MMC Tolerance = Hole (MMC) – Fastener (MMC) T = .324 – .312 T = .012

  13. Floating Fastener Hole Calculation Tolerance = .012 Fastener = .312 MMC Hole = Tolerance + Fastener (MMC) H = .012 + .312 H = .324 (MMC)

  14. Fixed Fastener Condition • Fastener passes through multiple holes, one fixes fastener location • Fastener fixed by threads, press fit, or taper

  15. Fixed Fastener Tolerance Calculation Hole = .296.003 Fastener = .250 MMC Tolerance = [Hole (MMC) – Fastener (MMC)]/2 T = (.293 – .250)/2 T = .0215

  16. Fixed Fastener Hole Calculation Tolerance = .0215 Fastener = .250 MMC Hole = 2  Tolerance + Fastener (MMC) H = (2  .0215) + .250 H = .293 (MMC)

  17. Advantages of Position Tolerances over Coordinate Tolerances • Clearer definition of requirements • Is no standard defining coordinate location tolerances • Increased tolerance zone area • Bonus tolerance is available

  18. Calculating Diameter of Position Variation

  19. Paper Gaging Position Variation • Center of graph is true position • Plot delta coordinate values for feature locations on graph • Create concentric circles representing tolerance zones at same scale as the graph grid

  20. Paper Gaging Example

  21. Counterbored Holes—Application Options • One position tolerance to control hole and counterbore • Separate position tolerances for the hole and counterbore • Counterbore position tolerance referenced to the hole location

  22. Threads—Application • Position tolerance applied to pitch axis • Position tolerance may be applied to minor or major diameter in rare cases

  23. Projected Tolerance Zone

  24. Bidirectional Position Tolerance

  25. Noncylindrical Features of Size • Slots, tabs, rails • No diameter symbol in the feature control frame • Do not place the feature control frame on an extension line • Defines the total width of the tolerance zone

  26. Bounded Feature

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