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8Position Tolerancing
Fundamentals
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
• 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.
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
• 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.
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Position Tolerances
• May be used on single or multiple features• Tolerance zone shape determined by functional
requirements for feature• Material condition modifiers are appropriate
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Feature Control Frame
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Material Condition Modifier Application
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Basic Dimensions
• Must be used to define location when position tolerances are applied to features
• Defines true position
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Effect of RFS
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Effect of MMC
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Proof of MMC Concept
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Floating Fastener Condition
• Fastener passes through multiple clearance holes
• Common to use same size clearance holes for all parts, but not required
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Hole = .328 .004Fastener = .312 MMC
Tolerance = Hole (MMC) – Fastener (MMC)
T = .324 – .312T = .012
Floating Fastener Tolerance Calculation
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Tolerance = .012Fastener = .312 MMC
Hole = Tolerance + Fastener (MMC)
H = .012 + .312H = .324 (MMC)
Floating Fastener Hole Calculation
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Fixed Fastener Condition
• Fastener passes through multiple holes, one fixes fastener location
• Fastener fixed by threads, press fit, or taper
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Hole = .296 .003Fastener = .250 MMC
Tolerance = [Hole (MMC) – Fastener (MMC)]/2
T = (.293 – .250)/2
T = .0215
Fixed Fastener Tolerance Calculation
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Tolerance = .0215Fastener = .250 MMC
Hole = 2 Tolerance + Fastener (MMC)
H = (2 .0215) + .250H = .293 (MMC)
Fixed Fastener Hole Calculation
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
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
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Calculating Diameter of Position Variation
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
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
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Paper Gaging Example
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
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
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Threads—Application
• Position tolerance applied to pitch axis• Position tolerance may be applied to minor or
major diameter in rare cases
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Projected Tolerance Zone
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Bidirectional Position Tolerance
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
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
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Bounded Feature
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