2. Section 2 Drafting Techniques and Skills
Chapter 9
Dimensioning Fundamentals
Section 2 Drafting Techniques and Skills

3. Objectives Define size and location dimensions.
Explain the drawing conventions used for dimension, extension, and leader lines.
Describe standard conventions used in inch dimensioning and metric dimensioning.
Identify and explain common dimensioning systems used in drafting.
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4. Objectives Explain the purpose of general and local notes.
List the general rules for good dimensioning practice.
Describe the common commands and methods used in dimensioning CAD drawings.
Dimension drawings using accepted conventions.
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5. Dimensions
Correct appearance and accuracy essential on detail drawings.
All line elements drawn thin.
Standard conventions provided in ASME Y14.5.
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6. Types of Dimensions Size dimensions Location dimensions
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7. Dimensioning Elements
Dimension line
Extension lines
Leaders
Arrowheads
Dimension figures
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8. Dimension Lines Used to indicate extent of dimension.
Spacing conventions apply.
Different practices used for placing numeral.
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9. Extension Lines Used to indicate termination of dimension.
Spacing conventions apply.
Lines crossing with others should be broken.
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10. Leaders Commonly used for notes and repetitive features.
Arrowhead used to terminate at edge.
Dot used to terminate inside object outline.
Angle should be 45 to 60.
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11. Dimensional Notes
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12. Arrowheads Drawn at same size as lettering height (usually .125").
Drawn freehand in manual drafting.
Generated automatically in CAD.
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13. Drawing Arrowheads Draw strokes forming each side. Draw curved base.
Fill in solid.
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14. Dimension Figures Drawn at same height as lettering height.
Fractions drawn at twice height of whole numbers.
Numerals staggered to save space and enhance appearance.
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15. Dimension Figure Placement
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16. Staggering Dimensions
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17. Dimension Placement Systems
Unidirectional dimensioning
Aligned dimensioning
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18. Dimensioning Within Object Outlines
Used in some cases for calling out feature directly.
Section lines broken when used on section views.
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19. Dimensioning Systems Decimal inch dimensioning Fractional dimensioning
Metric dimensioning
Dual dimensioning
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20. Decimal Inch Dimensioning
Commonly used in manufacturing applications.
Two-place decimals most common.
Common rules apply when rounding off values.
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21. Decimal Inch Dimensioning Conventions
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22. Fractional Dimensioning
Common in architectural and structural drafting.
Used for applications where close tolerances are unimportant.
Horizontal bar used for fractions.
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23. Metric Dimensioning Millimeter-dimensioned drawings most common.
Meters used for values greater than 10,000 mm.
Practice based on International System of Units (SI Metric system).
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24. Metric Dimensioning Conventions
Period used for decimal point (ASME standard).
Zero precedes decimal for values less than 1 mm.
Digits not grouped by commas or spaces.
Multiples of 1000 used for units (use of centimeters avoided).
Units not mixed with other systems.
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25. Dual Dimensioning Inch measurement typically given in decimal inches.
Metric measurement typically given in millimeters.
Metric-only drawings more common.
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26. Dual Dimensioning Conventions
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27. Features Dimensioned for Size
Cylindrical features
Circular arcs
Fillets and rounds
Round holes
Knurls
Angular dimensions
Chamfers
Counterbored holes
Spotfaced holes
Countersunk holes
Counterdrilled holes
Offsets
Keyseats
Undercuts
Tapers
Curves
Slotted holes
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28. Conventions for Cylindrical Features
Used for solid shapes and negative volumes (holes).
Diameter and length specified.
Diameter symbol used.
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29. Conventions for Circular Arcs
Radius specified.
Value preceded by “R.”
Dimension line typically drawn from center.
Leader dimensions may be used.
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30. Dimensioning Foreshortened Radii
Dimension line drawn radially.
Center of feature located with dimensions.
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31. Dimensioning True Radii
Done to clarify measurement appearing out of scale.
Note includes specification.
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32. Conventions for Fillets and Rounds
Radius specified.
Note used for many features of same size.
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33. Conventions for Round Holes
Diameter specified.
Leader dimensions used for small holes.
Dimension lines used for larger holes.
Hole depth indicated by note or section view.
(American National Standards Institute)
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34. Conventions for Knurls
Diameter, type, and pitch specified by note.
Length along axis specified if required.
Size and location dimensions typically combined.
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35. Conventions for Angular Dimensions
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36. Conventions for Chamfers
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37. Conventions for Counterbore and Spotface Dimensions
Diameter specified.
Same symbol used for both hole types.
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38. Conventions for Countersink and Counterdrill Dimensions
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39. Conventions for Offsets
Dimension from tangent point intersections.
Dimension along one side of part.
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40. Conventions for Keyseat Dimensions
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41. Conventions for Undercut Dimensions
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42. Conventions for Tapers
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43. Conventions for Curves
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44. Conventions for Rounded Ends
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45. Conventions for Slotted Holes
Length and width specified.
Longitudinal center and one end or centerline located.
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46. Methods for Dimensioning Features for Location
Point-to-point dimensioning
Coordinate dimensioning
Tabular dimensioning
Ordinate dimensioning
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47. Point-to-Point Dimensioning
Also called chain dimensioning.
Acceptable for simple parts.
One dimension omitted in chain for manufacturing.
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48. Coordinate Dimensioning Methods
Both types incorporate datum dimensioning.
Rectangular coordinate dimensioning
Polar coordinate dimensioning
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49. Rectangular and Polar Coordinate Dimensioning
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50. Tabular Dimensioning Form of rectangular coordinate dimensioning.
Useful for specifying many similar features.
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51. Ordinate Dimensioning
Datum planes specify zero coordinates.
Extension lines indicate dimensions.
Also known as arrowless dimensioning.
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52. Unnecessary Dimensions
Duplicate dimensions omitted.
Accumulation of tolerances avoided in chain dimensions.
Exceptions occur in architectural and structural drafting.
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53. Notes Used to clarify information and eliminate repetitive dimensions.
Aligned parallel to bottom of drawing.
Should be same height as other lettering.
Spacing between separate notes equal to twice lettering height.
Standard abbreviations used.
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54. General Notes Used for information applying to entire drawing.
Typically placed near or inside title block.
Often used to identify tolerances or materials.
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55. Local Notes Used to describe specific information.
Typically connected to leaders originating from features.
May be used with reference number and flag.
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56. General and Local Notes
(Autodesk, Inc.)
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57. Rules for Good Dimensioning
1. Plan layout to avoid crowding.
2. Draw all lines thin.
3. Dimension most descriptive contours.
4. Place dimensions between views and outside outlines.
5. Avoid crossing lines.
6. Dimension features to show relationships.
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58. Rules for Good Dimensioning (Cont.)
7. Dimension visible features.
8. State information clearly.
9. Include enough information to eliminate calculations.
10. Include only essential information.
11. Omit one dimension in chains.
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59. Dimensioning in CAD Generated with dimensioning commands.
Provides many advantages over manual dimensioning.
Dimension style settings provide great flexibility.
Same standards observed in manual drafting apply.
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60. Dimension Styles
Permit drafters to make definitions for various drafting applications.
Use ensures consistency and serves as reference.
Wide variety of settings available to meet standards.
Normally created with Dimstyle command.
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61. Dimension Style Settings
Unit settings
Dimension and extension line settings
Arrowhead and symbol settings
Text settings
Fit and scale settings
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62. Dimension Style Settings (Cont.)
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63. Unit Settings Format type for linear dimensions
Format type for angular dimensions
Precision controls
Zero suppression controls
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64. Dimension and Extension Line Settings
Spacing between adjacent dimension lines
Extension line offset from object
Extension line extension past dimension line
Line display color
Line suppression
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65. Arrowhead and Symbol Settings
Terminating symbol for dimension lines and leaders
Size of symbol
Center mark type and size
Arc length symbol placement
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66. Text Settings Text style Text height Display color
Placement in relation to dimension line
Alignment (unidirectional or aligned)
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67. Fit and Scale Settings
Placement of elements inside or outside extension lines
Size of all dimensioning elements
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68. Types of CAD Dimensions
Linear dimensions
Angular dimensions
Radial dimensions
Leader dimensions
Ordinate dimensions
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69. Types of Linear Dimensions
Horizontal
Vertical
Aligned
Datum
Chain
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70. Horizontal and Vertical Dimensions
Drawn with Linear dimension command.
Points picked to specify placement.
Text option used to modify dimension text.
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71. Aligned Dimensions Drawn with Aligned or Linear dimension command.
Points picked to specify placement.
Useful for angled features.
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72. Datum Dimensions Drawn with Baseline dimension command.
Points picked to specify base dimension and extension line origins.
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73. Chain Dimensions Drawn with Continue dimension command.
Points picked to specify base dimension and extension line origins.
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74. Angular Dimensions Drawn with Angular dimension command.
Used to dimension angle, included angle, or circle segment.
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75. Radial Dimensions Drawn with Radius or Diameter dimension command.
Points picked to select object and locate dimension.
Leader points to center.
Center mark drawn automatically.
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76. Leader Dimensions Drawn with Leader command.
Points picked to select feature and locate note text.
Commonly used for local notes.
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77. Ordinate Dimensions Drawn with Ordinate dimension command.
Points picked to select extension line origin and endpoint.
Dimensions measured from datum plane.
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78. Review Questions
1. The diameter of a cylinder is an example of a(n) _____ dimension.
A. size
B. angular
C. location
D. None of the above.
A. size
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79. Review Questions
2. _____ dimensioning is the standard practice in which dimension figures are placed to be read from the bottom of the drawing.
Unidirectional
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80. Review Questions
3. _____ are thin, straight lines that lead from a note or dimension to a feature on the drawing.
A. Dimension lines
B. Extension lines
C. Flags
D. Leaders
D. Leaders
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81. Review Questions
4. _____ dimensioning is commonly used for drawings made in architectural drafting.
A. Decimal inch
B. Metric
C. Fractional
D. Dual
C. Fractional
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82. Review Questions
5. Which of the following is true in relation to metric dimensioning?
A. Zeroes are omitted before the decimal point for numerical values of less than one.
B. Most metric drawings are dimensioned in centimeters.
C. Commas are used to separate digits in metric dimensions into groups.
D. Multiples of 1000 are used for metric values whenever possible.
D. Multiples of 1000 are used for metric values
whenever possible.
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83. Review Questions
6. Circular arcs are dimensioned by specifying the _____.
radius
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84. Review Questions
7. Hole features are dimensioned by specifying the _____.
diameter
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85. Review Questions
8. A(n) _____ is a beveled edge cut in a hole to permit a flat head screw to seat flush with the surface.
A. countersink
B. counterbore
C. knurl
D. offset
A. countersink
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86. Review Questions
9. Rectangular coordinate dimensioning is also known as _____ dimensioning.
A. chain
B. datum
C. point-to-point
D. leader
B. datum
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87. Review Questions
10. Designating a standard part is an example of a use for _____ notes.
local
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88. Review Questions
11. Which of the following is true in relation to dimensioning?
A. Dimensions should be drawn to hidden lines whenever possible.
B. All lines for dimensions are drawn thick.
C. Dimension text is drawn at the same height as other text on the drawing.
D. Dimensions should be duplicated between views.
C. Dimension text is drawn at the same height as other text on the drawing.
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89. Review Questions
12. The _____ dimensioning command is used to create datum dimensions.
A. Aligned
B. Baseline
C. Continue
D. Angular
B. Baseline
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90. Review Questions
13. Linear dimensioning commands are used to dimension _____.
A. notes
B. horizontal and vertical lines
C. arcs
D. circles
B. horizontal and vertical lines
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91. Glossary Aligned dimensioning
A dimensioning system in which all dimensions are placed parallel to their dimension lines and are read from the bottom or right side of the drawing.
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92. Glossary Arrowless dimensioning
A rectangular coordinate dimensioning system in which dimensions are measured from two or three mutually perpendicular datum planes but the datum planes are indicated as zero coordinates and dimensions are shown on extension lines without the use of dimension lines or arrowheads. Also known as ordinate dimensioning.
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93. Glossary Chain dimensioning
Type of dimensioning in which dimensions are placed in a “chain” from point to point to locate features. Also known as point-to-point dimensioning.
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94. Glossary Coordinate dimensioning Counterbore
A dimensioning system in which all dimensions are measured from two or three mutually perpendicular datum planes.
Counterbore
A recess that allows fillister or socket head screws to be seated below the surface of a part.
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95. Glossary Counterdrill Countersink
The combination of a small recess and a larger recess with a chamfered edge cut in a hole to allow room for a fastener.
Countersink
A beveled edge (chamfer) cut in a hole to permit a flat head screw to seat flush with the surface.
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96. Glossary Datum dimensioning Dimensional notes
Type of dimensioning in which all dimensions are from two or three mutually perpendicular datum planes.
Dimensional notes
Notes commonly placed with leaders to describe the size or form of features, such as hole specifications, chamfers, and threads.
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97. Glossary Dimension lines Dimension style
Thin lines terminated by arrowheads, used to indicate the extent and direction of dimensions.
Dimension style
In CAD applications, a set of parameters used to control the appearance of individual dimensioning elements.
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98. Glossary Extension lines Keyseat Knurls
Thin lines used to indicate the termination of a dimension.
Keyseat
A recess machined in a shaft to fit a key.
Knurls
Straight-line or diagonal-line serrations on a part used to provide a better grip or interference fit.
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99. Glossary Leaders Location dimensions
Thin lines drawn to notes or identification symbols used to clarify features.
Location dimensions
Dimensions that define the location of geometric components in relation to each other.
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100. Glossary Ordinate dimensioning
A rectangular coordinate dimensioning system in which dimensions are measured from two or three mutually perpendicular datum planes but the datum planes are indicated as zero coordinates and dimensions are shown on extension lines without the use of dimension lines or arrowheads. Also known as arrowless dimensioning.
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101. Glossary Point-to-point dimensioning
Type of dimensioning in which dimensions are placed in a “chain” from point to point to locate features. Also known as chain dimensioning.
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102. Glossary Polar coordinate dimensioning
Type of dimensioning used when holes or other features to be located lie in a circular or radial pattern. A radial (linear) dimension and angular dimensions originating from datum planes are given.
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103. Glossary Rectangular coordinate dimensioning
Type of dimensioning useful in locating holes and other features that lie in a rectangular or noncircular pattern. Dimensions are at right angles to each other and originate from common origins such as centerlines.
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104. Glossary SI Metric system Size dimensions
The metric system of weights and measures, recognized as the international standard. Referred to internationally as the International System of Units.
Size dimensions
Dimensions that define the size of geometric components of a part.
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105. Glossary Spotface Tabular dimensioning
A machined circular spot on the surface of a part to provide a flat bearing surface for a screw, bolt, nut, washer, or rivet head.
Tabular dimensioning
A rectangular coordinate dimensioning system in which dimensions from mutually perpendicular datum planes are listed in a table on the drawing and not applied directly to the views.
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106. Glossary Tolerance Undercut
The total amount of variation permitted from the design size of a part.
Undercut
A recess at a point where a shaft changes size and mating parts must fit flush against a shoulder.
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107. Glossary Unidirectional dimensioning
A standard dimensioning system in which all dimension figures are placed to be read from the bottom of the drawing.
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