Form Tolerances

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5. Form Tolerances. Apply straightness tolerances to control surface elements or a derived median line (commonly known as axis straightness) and show the interpretation of those tolerances. Apply flatness to control a surface and show an interpretation of the flatness tolerance zone. - PowerPoint PPT Presentation

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GD&T Application and Interpretation© Goodheart-Willcox Co., Inc.
Apply straightness tolerances to control surface elements or a derived median line (commonly known as axis straightness) and show the interpretation of those tolerances.
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
Apply flatness to control a surface and show an interpretation of the flatness tolerance zone.
Apply a flatness tolerance for a median plane and show an interpretation of the flatness tolerance zone.
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
Apply circularity tolerances and show an interpretation of a circularity tolerance zone.
Apply a cylindricity tolerance and show an interpretation of the cylindricity tolerance zone.
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
Form Tolerance Symbols
© Goodheart-Willcox Co., Inc.
© Goodheart-Willcox Co., Inc.
Material Condition Modifiers
MMC Applied when omission of MMC could increase cost
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
As size departs from MMC, form may vary
Perfect form not required at LMC
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
Control derived median line (Axis)
Surface line element may be called a line element or surface element
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
Center line is center of feature, no variation
Axis is line at center of actual mating envelope
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
to Surface Elements
Form tolerance only applied if the required control is smaller than the size tolerance
Form tolerance larger than size tolerance only permitted with independency symbol
Material condition modifiers not used in form tolerance specifications applied to surfaces
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
Direction dictated by view orientation
Straightness does not imply parallelism
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
Feature control frame with extension line or leader
Surface straightness does not control axis
Axis straightness does not control surface
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
© Goodheart-Willcox Co., Inc.
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
© Goodheart-Willcox Co., Inc.
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
Total allowable form tolerance equals specified form tolerance plus bonus tolerance
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
Overall and Unit
Unit length tolerance makes part easier to produce
Combination of overall and unit length tolerances may be best approach
Combination is specified by one feature control frame with upper and lower segments
Overall limits accumulation of unit length
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
© Goodheart-Willcox Co., Inc.
Gage for Unit
© Goodheart-Willcox Co., Inc.
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
© Goodheart-Willcox Co., Inc.
© Goodheart-Willcox Co., Inc.
Overall and Unit Area Flatness Tolerance
Combination of overall and unit area tolerances may be best approach
Combination is specified by one feature control frame with upper and lower segments
Overall controls accumulation of unit area
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
Flatness Tolerance Applied to a Derived Median Plane
Feature control frame placed adjacent to dimension or on dimension line
No leader
© Goodheart-Willcox Co., Inc.
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
Only applied as a control of surface form
No material condition modifier
Applies at each cross section
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
Only applied as a control of surface form
No material condition modifier
Applies at each cross section
Does not control the angle
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
Is combination of circularity and straightness
Two concentric cylinders create boundary
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
Actual mating envelope
A true geometric counterpart of the feature that is at the maximum size that will fit within the hole or other internal feature or at the minimum size that will encompass a shaft or other external feature.
Bonus tolerance
Any increase in allowable tolerance that is permitted by the departure of a feature from the material condition specified in the feature control frame.
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
Center line
A line that represents the center of a feature on a drawing or in a CAD model
Circularity
Establish the allowable variation on the roundness of any feature that has a circular cross section, including cylinders, cones, and spheres.
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
Coordinate measuring machine (CMM)
A machine that electronically records coordinates for features on a part. A coordinate measuring machine may also calculate feature variations from nominal and report an existing discrepancies.
Cylindricity
The allowable form variance of a surface bounded by two concentric cylinders.
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
Derived median line
A line that may not be straight that is made of the mid points between two surface elements that are on opposite side of the feature or by center points along the length of the cylindrical shape.
Envelope principle
The controlled feature must be within a boundary of perfect form at MMC.
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
Feature control frame
A tolerance specification in a format that shows the tolerance type, tolerance value, any applicable material condition modifiers, and any applicable datum feature references.
Flatness
The allowable form variance of a surface bounded by two parallel planar surfaces.
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
Free state variation
The condition of a part that permits its dimensions to change after the part is removed from the manufacturing equipment.
Full indicator movement (FIM)
The difference between the minimum and maximum reading obtained with a dial indicator. Full indicator movement is also referred to as total indicator reading (TIR).
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
Functional gage
A tool that can be used to check dimension limits by placing the gage on or in the workpiece. An example is a plate with four pins that check the locations of four holes.
Rule #1
Any dimensional feature of size must have perfect form when the feature is produced at its maximum material condition.
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
Straightness
The allowable form variance of surface elements or a derived median line for a regular feature of size bounded by parallel straight lines.
Surface line element
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
A graphical representation of the controls within the form, orientation, profile, location, runout, and miscellaneous categories.
Tolerance value, feature control frame
The number following the tolerance symbol. This value indicates the permitted amount of variation.
GD&T: Application and Interpretation
© Goodheart-Willcox Co., Inc.
Total indicator reading (TIR)
The difference between the minimum and maximum reading obtained with a dial indicator. Total indicator movement is also referred to as full indicator movement (FIM).
Virtual condition