Post on 14-Feb-2016
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5Form Tolerances
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
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Form Feature Control Frame
• Has only two compartments– Tolerance symbol– Tolerance value
• No datum feature references
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Material Condition Modifiers
• RFS assumed• MMC symbol must be shown when applicable• MMC Applied when omission of MMC could
increase cost
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Form Requirements from Size Limits
• Size limit controls form• Maximum material condition (MMC), small hole
or large shaft• Least material condition (LMC), small shaft or
large hole
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Rule #1
• Perfect form boundary at MMC• As size departs from MMC, form may vary• Perfect form not required at LMC
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Perfect Form Boundary Effect on Flat Surfaces
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Perfect Form Boundary Effect On Cylinders
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Straightness
• Control surface elements• 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.
Straightness (Cont.)
• Derived median line made from midpoints• 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.
Straightness Applied 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.
Straightness of Flat Surfaces
• Feature control frame with extension line or leader
• Direction dictated by view orientation• Straightness does not imply parallelism
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Straightness of Cylinder Surface Elements
• Variation of surface element straightness• 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.
Straightness of Cone Elements
• Each cone element controlled independently• Angle controlled by other means
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Verification of Surface Straightness
• Use a dial indicator– Full indicator movement (FIM)– Total indicator reading (TIR)
• Use a straight edge and feeler gage
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Straightness Applied to Features of Size
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Straightness to Control a Shaft Derived Median Line
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Bonus Tolerance
• Allowable only when MMC is applied• Equals departure of size from MMC • Total allowable form tolerance equals specified
form tolerance plus bonus tolerance
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Straightness of the Derived Median Line of a Hole
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Overall and Unit Length Tolerance
• 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.
Gage for Overall Straightness
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Gage for Unit Length Straightness
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Flatness
• No material condition modifier applicable on a surface
• RFS or MMC applicable on feature of size
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Flatness Applied to a Surface
• Only tolerance symbol and value• Surface variations limited by size
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Verification of Surface Flatness
GD&T: Application and Interpretation © 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
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Verification of Derived Median Plane Flatness
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Circularity Applied to a Cylindrical Surface
• Only applied as a control of surface form• No material condition modifier• Tolerance zone between two concentric circles• Applies at each cross section
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Circularity Applied to a Cone
• Only applied as a control of surface form• No material condition modifier• Tolerance zone between two concentric circles• Applies at each cross section• Does not control the angle
GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.
Cylindricity
• Applicable to shaft or hole• Is combination of circularity and straightness• Two concentric cylinders create boundary