2. Section 4 Advanced Applications
Chapter 16
Geometric Dimensioning and Tolerancing
Section 4 Advanced Applications

3. Objectives
Define the common terms used in geometric dimensioning and tolerancing applications.
List and describe the different types of tolerances used to control fits for machine parts.
Identify specific symbols used in geometric dimensioning and tolerancing applications.
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4. Objectives
Explain the standard practices for applying tolerance dimensions to drawings.
Describe how tolerance dimensions are created on CAD drawings.
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5. Tolerancing
Used to control dimensions to allow for interchangeable manufacture.
Applied based on engineering needs.
Industry standards
Practice
Part function
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6. Types of Tolerances Positional tolerances Form tolerances
Profile tolerances
Orientation tolerances
Runout tolerances
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7. Tolerancing Terms Basic dimension Reference dimension Datum
Nominal size
Basic size
Actual size
Allowance
Design size
Limits
Tolerance
Fit
Maximum material condition (MMC)
Least material condition (LMC)
Regardless of feature size (RFS)
Selective assembly
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8. Basic Dimension
Used to establish “base” for associated dimensions and tolerances.
Not directly toleranced.
Indicated by enclosing dimension in rectangle.
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9. Reference Dimension
Specified for engineering personnel or manufacturer.
Untoleranced and not used in manufacture.
Indicated by enclosing dimension in parentheses.
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10. Datum Typically designated as plane or point.
Identified by datum feature symbol.
May be specified as primary, secondary, or tertiary.
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11. Nominal Size
Typically used as classification for manufactured products.
May or may not identify actual size.
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12. Basic Size and Design Size
Allowance provides for class of fit.
Assigned tolerance determines design size.
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13. Tolerance Specifies total variation permitted from design size.
Does not indicate allowance.
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14. Types of Tolerances Unilateral tolerance Bilateral tolerance
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15. Types of Fits Clearance fit Interference fit Transition fit
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16. Basic Size Systems Basic hole size system Basic shaft size system
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17. Basic Hole Size System Basic hole size assigned as minimum hole size.
Allowance applied to shaft.
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18. Basic Shaft Size System
Basic size assigned as maximum shaft size.
Allowance applied to hole.
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19. Not-to-Scale Dimensions
May be used in drawing revisions if meaning remains clear.
Indicated by thick line underneath dimension.
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20. Tolerance Application Dimensioning Methods
Limit dimensioning
Plus and minus tolerancing
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21. Dimensioning Systems for Location Dimensions
Chain dimensioning
Datum dimensioning
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22. Chain Dimensioning May result in excessive tolerance accumulation.
Used with basic dimensions in incremental positioning applications.
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23. Datum Dimensioning Avoids tolerance accumulation.
Also called baseline dimensioning.
Used in absolute positioning applications.
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24. Angular Surface Tolerancing
Applies linear and angular dimensions or linear dimensions alone.
Used to specify angular tolerance zone.
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25. Specifying Fits Standard tables used for reference by drafters.
Part function determines selection.
Tolerance dimensions specify fit (fit not specified on drawing).
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26. Standard Fits Running and sliding fits Locational fits Force fits
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27. Running and Sliding Fits
Designed to describe running performance of mating parts.
Subtypes designated by letter symbols RC.
RC1 (Close sliding fits)
RC2 (Sliding fits)
RC3 (Precision running fits)
RC4 (Close running fits)
RC5 and RC6 (Medium fits)
RC7 (Free running fits)
RC8 and RC9 (Loose running fits)
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28. Locational Fits Designed to describe location of mating parts.
Subtypes relate to tightness or looseness of fit.
LC (Locational clearance fits)
LT (Locational transition fits)
LN (Locational interference fits)
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29. Force Fits Designed to describe pressures between mating parts.
Also called shrink fits and press fits.
Subtypes designated by letter symbols FN.
FN1 (Light drive fits)
FN2 (Medium drive fits)
FN3 (Heavy drive fits)
FN4 and FN5 (Force fits)
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30. Geometric Dimensioning and Tolerancing
Used to describe function and relationship of mating parts.
Provides for interchangeability of parts.
Designed to permit maximum variation from design size.
Applied in conjunction with coordinate dimensioning systems.
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31. Geometric Characteristic Symbols
Used to explain tolerance specifications.
May be generated with templates in manual drafting.
May be created using special commands in CAD.
(American Society of Mechanical Engineers)
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32. Geometric Dimensioning and Tolerancing Modifying Symbols
(American Society of Mechanical Engineers)
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33. Datum Features Identified by datum feature symbols.
Datum target used when needed to identify only part of feature.
Material condition symbols used as modifiers when applicable.
(American Society of Mechanical Engineers)
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34. Feature Control Frame
Datum reference letters appear in order of preference.
Material condition symbols used as modifiers when applicable.
(American Society of Mechanical Engineers)
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35. Feature Control Frame Conventions
(American Society of Mechanical Engineers)
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36. Positional Tolerances
Used to specify locations of features in relation to features or datums.
Also called location tolerances.
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37. Types of Positional Tolerances
True position
Concentricity
Symmetry
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38. True Positional Tolerance
Used to specify amount of variation from true position.
Indicated by position symbol in feature control frame.
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39. Cylindrical Tolerance Zone
(American Society of Mechanical Engineers)
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40. Projected Tolerance Zone
Used to specify position critical to mating parts.
Indicates extent in relation to feature.
(American Society of Mechanical Engineers)
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41. True Positional Tolerance Zone for Noncircular Features
Applies to center plane of feature.
Used for slots, tabs, and elongated holes.
(American Society of Mechanical Engineers)
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42. Concentricity (American Society of Mechanical Engineers)
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43. Symmetry Used to indicate variation from centerline or center plane.
May be specified using positional tolerance.
(American Society of Mechanical Engineers)
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44. Form Tolerances Straightness Flatness Circularity Cylindricity
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45. Straightness Used to describe variation of surface from straight line.
May be applied in single direction or in two directions.
(American Society of Mechanical Engineers)
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46. Flatness
Used to describe variation of surface elements lying in single plane.
(American Society of Mechanical Engineers)
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47. Circularity
Used to describe variation of surface elements from axis in relation to intersection plane.
Also referred to as “roundness.”
May be applied to cylindrical, conical, or spherical surfaces.
(American Society of Mechanical Engineers)
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48. Cylindricity
Used to describe variation of surface elements from axis of revolution.
Tolerance zone defines annular space.
Also controls roundness, straightness, and parallelism.
(American Society of Mechanical Engineers)
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49. Profile Tolerances
Used to describe variations in elements making up profile.
Specified in conjunction with basic dimensions.
May specify profile of surface or profile of line.
(American National Standards Institute)
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50. Profile Tolerance Specification
(American Society of Mechanical Engineers)
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51. Orientation Tolerances
Angularity
Parallelism
Perpendicularity
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52. Angularity
Used to describe angular orientation of surface in relation to datum plane or axis.
(American Society of Mechanical Engineers)
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53. Parallelism
Used to describe parallel relationship of surface to datum plane or axis.
(American Society of Mechanical Engineers)
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54. Perpendicularity
Used to describe perpendicular relationship of surface to datum plane or axis.
(American Society of Mechanical Engineers)
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55. Runout Tolerances Circular runout Total runout
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56. Circular Runout
Used to describe runout of individual features as part is rotated about axis.
Controls circularity and cylindricity.
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57. Total Runout
Used to describe runout of all surface elements indicated when part is rotated about axis.
Controls circularity and cylindricity for part as a whole.
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58. Runout Control (American Society of Mechanical Engineers)
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59. Surface Texture
Indicated with other dimensions on drawing when required.
Consists of three primary characteristics:
Roughness
Waviness
Lay
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60. Surface Texture (Cont.)
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61. Surface Texture Measurements
Roughness height
Roughness width
Roughness-width cutoff
Waviness width
Waviness height
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62. Surface Texture Symbol Conventions
Symbol may rest on surface or extension line.
Leader may be used with symbol when directed to surface.
Lay symbol located below horizontal bar when used.
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63. Geometric Dimensioning and Tolerancing on CAD Drawings
Special commands often used to generate tolerancing symbols.
Dimension styles typically defined to create tolerance dimensions.
Basic dimensions
Limit dimensions
Plus and minus tolerancing dimensions
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64. CAD-Generated Tolerancing
Basic dimensions generated automatically.
Tolerance command used to create feature control frame.
Leader command used in separate operation to place note.
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65. Review Questions
1. A _____ dimension is an exact dimension used to describe size, shape, or location and is enclosed in a rectangular frame.
A. reference
B. not-to-scale
C. limit
D. basic
D. basic
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66. Review Questions
2. A _____ symbol consists of a reference letter enclosed in a square frame.
A. surface texture
B. datum reference
C. material condition
D. projected tolerance zone
B. datum reference
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67. Review Questions
3. The _____ is the intentional difference in the dimensions of mating parts to provide for different classes of fits.
A. allowance
B. tolerance
C. actual size
D. nominal size
A. allowance
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68. Review Questions
A(n) _____ tolerance varies in only one direction from the specified dimensions.
unilateral
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69. Review Questions
5. Which of the following is true in relation to datum dimensioning?
A. It is designed so that features are dimensioned from point to point.
B. It is used in incremental positioning CNC operations.
C. It is also referred to as “chain dimensioning.”
D. It avoids tolerance accumulation.
D. It avoids tolerance accumulation.
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70. Review Questions
_____ fits are special interference fits normally characterized by constant bore pressures.
A. Locational
B. Locational transition
C. Force
D. Running and sliding
C. Force
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71. Review Questions
7. Which of the following is not a positional tolerance?
A. Angularity
B. Concentricity
C. Symmetry
D. True position
A. Angularity
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72. Review Questions
8. _____ describes how close all elements of a surface are to being in one plane.
A. Straightness
B. Flatness
C. Circularity
D. Symmetry
B. Flatness
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73. Review Questions
9. _____ tolerances are used to establish allowable variations in the individual line elements making up surfaces.
A. Runout
B. Orientation
C. Profile
D. Location
C. Profile
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74. Review Questions
10. The _____ command is used to create feature control frames.
A. Tolerance
B. Style
C. Offset
D. Text
A. Tolerance
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