2. Section 2 Drafting Techniques and Skills
Chapter 11
Pictorial Drawings
Section 2 Drafting Techniques and Skills

3. Objectives
List the three basic types of pictorial drawings and explain the purpose of each.
Explain the principles of axonometric projection.
Draw isometric, dimetric, and trimetric views.
Draw oblique views.
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4. Objectives Draw one-point and two-point perspective views.
Describe how pictorial views are created in CAD drafting.
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5. Pictorial Drawing Often used with or in place of multiview drawing.
Commonly made for assemblies and piping designs.
Widely used in service manuals and training materials.
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6. Types of Pictorial Projections
(American National Standards Institute)
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7. Types of Axonometric Projection
Isometric
Dimetric
Trimetric
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8. Isometric Projection Three faces equally inclined to projection plane.
Axis angles equal.
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9. Dimetric Projection
Two of three faces equally inclined to projection plane.
Two axis angles equal.
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10. Trimetric Projection
Three faces inclined differently to projection plane.
Axis angles all unequal.
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11. Isometric Projection
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12. Principles of Isometric Projection
Isometric axes separated by 120.
Object faces make up isometric planes.
View made up of isometric lines and nonisometric lines.
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13. Comparing Isometric Projection and Isometric Drawing
Isometric drawings more common (easier to make).
Isometric drawings made with direct measurements.
Lines foreshortened in isometric projection.
(American National Standards Institute)
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14. Constructing Isometric Drawings
Normal surfaces drawn before inclined surfaces.
Lines parallel to horizontal axes drawn at 30.
Lines parallel to vertical axis drawn vertical.
Hidden lines normally omitted.
Same principles apply in manual drafting and CAD.
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15. Isometric Drawing Functions in CAD
Isometric snap
Isoplanes
Isometric grid
Isometric viewing tools
Modeling commands
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16. Isoplane Orientations
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17. Construct an Isometric Drawing with Normal Surfaces
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18. Construct an Isometric Drawing with Normal Surfaces
Activate isometric snap.
Use Line command and Ortho to draw outer isometric lines.
Draw isometric lines to create cut surface.
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19. Construct an Isometric View with Nonisometric Lines
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20. Construct an Isometric View with Nonisometric Lines
Activate isometric snap.
Use drawing and editing commands to create isometric lines.
Use drawing commands and object snaps to create nonisometric lines.
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21. Construct Angles in an Isometric Drawing
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22. Construct Angles in an Isometric Drawing
Activate isometric snap.
Use Line command to create isometric lines.
Use Copy and Line commands to create angle cuts.
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23. Methods Used to Construct Isometric Circles and Arcs
Four-center approximate method
Coordinate method
Isometric ellipse template
Ellipse command
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24. Four-Center Approximate Method
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25. Draw Isometric Circles and Arcs Using the Ellipse Command
Activate isometric snap and desired isoplane.
Enter Ellipse command and enter Isocircle option.
Pick ellipse center and drag to specify radius.
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26. Draw Irregular Curves in Isometric Drawings
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27. Draw Irregular Curves in Isometric Drawings
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28. Constructing Isometric Section Views
Cutting plane drawn parallel to isometric axis.
Section lines normally drawn at 60.
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29. Draw an Isometric Section View
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30. Draw an Isometric Section View
Draw isometric outlines and sectioned faces.
Draw isometric circles and arcs.
Add hatch lines.
Use Section Plane command in 3D applications.
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31. Isometric Dimensioning
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32. Alternate Positioning of Isometric Axes
Used to clarify important features.
Axes must remain oriented at 120.
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33. Centering an Isometric Drawing
Locate object center.
Locate center point at center of sheet.
Locate start point from center parallel to isometric axes.
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34. Advantages and Disadvantages of Isometric Drawings
Same scale used on all three axes.
Single view sufficient.
Less time required than in other pictorial methods.
Disadvantages
Potential distortion of long objects.
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35. Dimetric Projection Two axes making equal angles drawn at same scale.
Third axis drawn at different scale.
May be constructed by using revolution or auxiliary view.
Approximate dimetric drawings more common.
Common scale and axis combinations available.
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36. Constructing a Dimetric Projection
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37. Common Dimetric Axis Angle and Scale Combinations
Used to simplify constructions in manual drafting.
May be used with polar coordinates and tracking in 2D CAD drawings.
Modeling and 3D viewing commands more typical in CAD.
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38. Creating Dimetric Drawings in CAD
Model created using 3D drawing commands.
View oriented using 3D viewing commands.
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39. Trimetric Projection Axes drawn at three different scales.
Approximate trimetric drawings more common.
Common scale and axis combinations available.
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40. Constructing a Trimetric Projection
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41. Common Trimetric Axis Angle and Scale Combinations
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42. Constructing Circles in Dimetric and Trimetric Views
Ellipse template is used in manual drafting.
Auxiliary view method is most appropriate to determine ellipse angles.
Ellipse angles for dimetric drawing are equal in two axis planes.
Ellipse angles for trimetric drawing differ for each plane.
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43. Construct Circles in a Dimetric or Trimetric Drawing
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44. Advantages and Disadvantages of Dimetric and Trimetric Drawings
Number of viewing positions unlimited.
Common axis angles and scales simplify construction.
Disadvantages
Views more difficult to draw than other pictorials.
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45. Oblique Projection
Front view projected parallel to projection plane (true size).
Projectors parallel to lines of sight.
Oblique drawing less time-consuming and more common.
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46. Oblique Drawing Types Cavalier oblique Cabinet oblique General oblique
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47. Cavalier Oblique Receding axis typically oriented at 45.
Receding axis and front axes drawn true length.
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48. Cabinet Oblique
Receding axis angle varies (30, 45, and 60 typical).
Receding axis drawn at half scale.
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49. General Oblique Receding axis angle varies from 0 to 90.
Receding axis drawn between half and full scale.
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50. Constructing Angles in Oblique Drawings
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51. Constructing Arcs, Circles, and Curves in Oblique Drawings
Features on front plane projected true size.
Construction methods required on other planes.
Ellipses may be drawn on cavalier oblique planes in CAD.
3D modeling and viewing commands more common in CAD applications.
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52. Constructing Arcs, Circles, and Curves in Oblique Drawings
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53. Selecting Views and Positions for Oblique Drawings
To minimize distortion, orient long axes parallel to front plane.
To show bottom surfaces, reverse direction of depth axis.
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54. Oblique Dimensioning Conventions
Similar to isometric dimensioning.
Unidirectional system preferred.
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55. Advantages and Disadvantages of Oblique Drawings
Features on front plane can be drawn true size.
Different types allow for control over scaling.
Disadvantages
Receding plane features take longer to draw.
Long objects may appear distorted.
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56. Perspective Drawing Most realistic form of pictorial drawing.
Types classified by number of vanishing points used.
Drawing layout principles more suitable for manual drafting than CAD.
3D modeling and viewing commands used in CAD.
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57. Types of Perspective Drawings
(American National Standards Institute)
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58. Perspective Drawing Terms
Station point
Vanishing points
Visual rays
Picture plane
Horizon line
Ground line
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59. Horizon Line Placement
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60. One-Point Perspective
Lines converge to single vanishing point.
Frontal plane parallel to picture plane.
Also called parallel perspective.
Commonly used to illustrate interior construction.
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61. Construct a One-Point Perspective Drawing
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62. Construct a One-Point Perspective Drawing (Cont.)
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63. Two-Point Perspective
Lines converge to two vanishing points.
Object planes inclined to picture plane.
Also called angular perspective.
Commonly used to illustrate large structures.
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64. Construct a Two-Point Perspective Drawing
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65. Construct a Two-Point Perspective Drawing (Cont.)
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66. Perspective Views of Objects Lying Behind the Picture Plane
Extend lines from top view to locate piercing points.
Project verticals to ground line to locate true length lines.
Draw receding planes and project points from top view.
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67. Drawing Circles in Perspective Views
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68. Construct Circles on Inclined Vertical Perspective Planes
Divide front view and transfer points to top view.
Project points to perspective view and to vanishing point.
Project divisions from picture plane to perspective view.
Draw perspective ellipse with template.
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69. Construct Circles on Inclined Horizontal Perspective Planes
Divide circle in top view and project points to sides.
Project true length vertical “height” line.
Project points from picture plane to perspective view.
Project receding lines to locate ellipse points.
Draw perspective ellipse with template.
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70. Perspective Drawing Instruments
Perspective grid
Perspective drawing board
Irregular curve
Ellipse templates
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71. Sketch a Perspective Drawing
Locate vanishing points on horizon line.
Sketch true length “height” line and receding lines.
Sketch vertical lines at half scale to locate frontal planes.
Sketch top surface.
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72. CAD-Generated Pictorials
Most commonly created as 3D models rather than 2D drawings.
Typically made as renderings.
3D viewing commands normally used to orient view.
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73. Review Questions
1. In axonometric projection, the object faces are all _____ to the plane of projection.
inclined
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74. Review Questions
2. An isometric drawing is one type of _____ projection.
A. axonometric
B. perspective
C. orthographic
D. oblique
A. axonometric
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75. Review Questions
3. In an isometric projection, the three drawing axes make equal _____ angles with each other.
A. 30
B. 60
C. 90
D. 120
D. 120
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76. Review Questions
4. In CAD, the isometric drawing planes defined by the direction of the isometric axes are called the _____.
isoplanes
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77. Review Questions
5. In an isometric section view, section lines are normally drawn at an angle of _____.
60
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78. Review Questions
6. Isometric ellipses are drawn using the _____ command.
A. Spline
B. Section Plane
C. Ellipse
D. Circle
C. Ellipse
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79. Review Questions
7. Which of the following is not used to construct isometric circles in manual drafting?
A. Ellipse template
B. Trammel method
C. Four-center approximate method
D. Coordinate method
B. Trammel method
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80. Review Questions
8. The frontal plane of a(n) _____ drawing is parallel to the projection plane.
A. dimetric
B. trimetric
C. oblique
D. isometric
C. oblique
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81. Review Questions
9. A(n) _____ oblique drawing has the receding axis drawn at full scale.
cavalier
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82. Review Questions
10. In a(n) _____ perspective drawing, receding lines converge to a single vanishing point.
A. one-point
B. two-point
C. three-point
D. angular
A. one-point
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83. Review Questions
11. The _____ is an assumed point representing the position of the observer’s eye in a perspective view.
A. ground line
B. station point
C. vanishing point
D. picture plane
B. station point
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84. Review Questions
12. The vanishing points are located on the _____ in a perspective view.
A. ground line
B. horizon line
C. projection plane
D. picture plane
B. horizon line
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85. Glossary Axonometric projection Dimetric projection
A projection method in which the projectors are perpendicular to the projection plane, but the faces of the object are inclined to the projection plane to achieve a pictorial effect.
Dimetric projection
A projection method in which two object faces are equally inclined to the plane of projection and two of the object axes make equal angles with each other.
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86. Glossary Foreshortened Isometric axes Isometric grid
Drawn shorter than true length.
Isometric axes
The normal drawing axes separated by equal angles of 120° in an isometric projection.
Isometric grid
A CAD function used to orient the drawing grid to an isometric pattern to aid in isometric drawing.
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87. Glossary Isometric planes Isometric projection
The regular isometric drawing planes used in constructing isometric views.
Isometric projection
A projection method in which all three principal faces of the object are equally inclined to the projection plane. Also, all three axes make equal angles with each other.
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88. Glossary Isometric snap Isoplanes
A CAD function that allows you to draw lines along isometric axes.
Isoplanes
In CAD applications, the left, right, and top drawing planes defined by the direction of the isometric axes.
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89. Glossary Normal surfaces Oblique projection
Surfaces that are parallel to the principal planes of projection.
Oblique projection
A form of one-plane projection in which the projectors are parallel to each other, but they meet the plane of projection at an oblique angle.
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90. Glossary Perspective drawing Pictorial drawing
A pictorial drawing in which receding lines converge at vanishing points on the horizon.
Pictorial drawing
A realistic, three-dimensional representation showing the width, height, and depth of an object.
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91. Glossary Trimetric projection
A projection method in which all three object faces make different angles with the plane of projection and the three object axes make different angles with each other.
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