Position Tolerancing Fundamentals 8 Position Tolerancing Fundamentals

Sketch the proper location and shape for position tolerance zones. 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. © 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. © 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 © Goodheart-Willcox Co., Inc.

Feature Control Frame © Goodheart-Willcox Co., Inc.

Material Condition Modifier Application © Goodheart-Willcox Co., Inc.

Basic Dimensions Must be used to define location when position tolerances are applied to features Defines true position © Goodheart-Willcox Co., Inc.

Effect of RFS © Goodheart-Willcox Co., Inc.

Effect of MMC © Goodheart-Willcox Co., Inc.

Proof of MMC Concept © 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 © Goodheart-Willcox Co., Inc.

Floating Fastener Tolerance Calculation Hole = .328 .004 Fastener = .312 MMC Tolerance = Hole (MMC) – Fastener (MMC) T = .324 – .312 T = .012 © Goodheart-Willcox Co., Inc.

Floating Fastener Hole Calculation Tolerance = .012 Fastener = .312 MMC Hole = Tolerance + Fastener (MMC) H = .012 + .312 H = .324 (MMC) © Goodheart-Willcox Co., Inc.

Fixed Fastener Condition Fastener passes through multiple holes, one fixes fastener location Fastener fixed by threads, press fit, or taper © Goodheart-Willcox Co., Inc.

Fixed Fastener Tolerance Calculation Hole = .296 .003 Fastener = .250 MMC Tolerance = [Hole (MMC) – Fastener (MMC)]/2 T = (.293 – .250)/2 T = .0215 © Goodheart-Willcox Co., Inc.

Fixed Fastener Hole Calculation Tolerance = .0215 Fastener = .250 MMC Hole = 2  Tolerance + Fastener (MMC) H = (2  .0215) + .250 H = .293 (MMC) © 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 © Goodheart-Willcox Co., Inc.

Calculating Diameter of Position Variation © 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 © Goodheart-Willcox Co., Inc.

Paper Gaging Example © 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 © 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 © Goodheart-Willcox Co., Inc.

Projected Tolerance Zone © Goodheart-Willcox Co., Inc.

Bidirectional Position Tolerance © 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 © Goodheart-Willcox Co., Inc.

Bounded Feature © Goodheart-Willcox Co., Inc.

Bidirectional position tolerance The allowable variance that permits more positional tolerance in one direction than the other.  © Goodheart-Willcox Co., Inc.

Fixed fastener condition An assembly condition in which two or more parts are stacked together with a fastener passed through them. One of the parts has a hole that in some manner fixes the location of the fastener. The hole may be threaded with the fastener threaded into it, or the hole may be sized for a press fit. © Goodheart-Willcox Co., Inc.

Floating fastener condition An assembly condition in which two or more parts are stacked together with a fastener passing through them. All of the parts have clearance holes in them. Paper gaging A method of analyzing collected inspection data to see if the part meets tolerance requirements. © Goodheart-Willcox Co., Inc.

Position tolerance zone A value that defines the acceptable amount of variation in the location of a feature relative to the true position specified for the feature. Position tolerance zone The three-dimensional boundary controlling the location of a feature.  © Goodheart-Willcox Co., Inc.

Projected tolerance zone A tolerance zone that extends to the outside of the controlled feature. True position A theoretically exact location for a feature. A specified tolerance defines the allowable variation relative to the true position. © Goodheart-Willcox Co., Inc.