1. 5
Form Tolerances

2. Apply straightness tolerances to control surface elements or a derived median line (commonly known as axis straightness) and show the interpretation of those tolerances.
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3. 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.
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4. 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.
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5. Form Tolerance Symbols
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6. Form Feature Control Frame
Has only two compartments
Tolerance symbol
Tolerance value
No datum feature references
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7. Material Condition Modifiers
RFS assumed
MMC symbol must be shown when applicable
MMC Applied when omission of MMC could increase cost
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8. 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
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9. Rule #1 Perfect form boundary at MMC
As size departs from MMC, form may vary
Perfect form not required at LMC
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10. Perfect Form Boundary Effect on Flat Surfaces
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11. Perfect Form Boundary Effect On Cylinders
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12. Straightness Control surface elements
Control derived median line (Axis)
Surface line element may be called a line element or surface element
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13. 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
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14. 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
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15. Straightness of Flat Surfaces
Feature control frame with extension line or leader
Direction dictated by view orientation
Straightness does not imply parallelism
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16. 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
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17. Straightness of Cone Elements
Each cone element controlled independently
Angle controlled by other means
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18. Verification of Surface Straightness
Use a dial indicator
Full indicator movement (FIM)
Total indicator reading (TIR)
Use a straight edge and feeler gage
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19. Straightness Applied to Features of Size
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20. Straightness to Control a Shaft Derived Median Line
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21. 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
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22. Straightness of the Derived Median Line of a Hole
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23. 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
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24. Gage for Overall Straightness
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25. Gage for Unit Length Straightness
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26. Flatness No material condition modifier applicable on a surface
RFS or MMC applicable on feature of size
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27. Flatness Applied to a Surface
Only tolerance symbol and value
Surface variations limited by size
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28. Verification of Surface Flatness
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29. 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
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30. Flatness Tolerance Applied to a Derived Median Plane
Feature control frame placed adjacent to dimension or on dimension line
No leader
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31. Verification of Derived Median Plane Flatness
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32. 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
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33. 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
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34. Cylindricity Applicable to shaft or hole
Is combination of circularity and straightness
Two concentric cylinders create boundary
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35. 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.
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36. Center line Circularity
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.
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37. 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.
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38. Derived median line Envelope principle
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.
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39. Feature control frame Flatness
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.
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40. Full indicator movement (FIM)
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).
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41. 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.
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42. Straightness Surface line element
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
A line on the surface of a part.
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43. Tolerance value, feature control frame
Tolerance symbol
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.
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44. 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
The combined effect of the maximum material condition and any applicable tolerance.
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