Orthographic projections are a method for conveying the shape and size of engineered objects using 2D drawings. They involve taking views of an object from the front, top, and side with parallel projecting rays. Lines and areas in the views represent edges, surfaces, and intersections between surfaces of the 3D object. Sectional views use a cutting plane to reveal internal features that would otherwise be hidden. They distinguish cut areas, which are hatched, from open areas cut through by the sectioning plane. Orthographic projections and sections effectively communicate 3D geometric information through 2D drawings.

1. Mechanical Sciences-IChapter 7: Orthographic Projections

2. Introduction to Orthographic ProjectionsIntroducing Orthographic Projections as the language of engineering designers

3. Orthographic ProjectionsOrthographic projections are an engineer’s language for conveying the shape and size information about the products he designs.

4. An orthographic projection consists of the view obtained view when the object is viewed from very far away, so that the resulting rays are all parallel.

5. The parallel rays that are used for constructing the views are called projectors.Vijay Gupta

6. Orthographic ProjectionsThe three principal views are take on picture planes which are held parallel to the three principal faces of the object, the front, the top and the side.

7. The intersections of the projectors with the picture plane are the projections of the points from which the projectors emanate.

8. The points are joined to obtain the views.Vijay Gupta

9. We consider here the development of the orthographic views of a simple object.ObjectVijay Gupta

10. For the Top view we view from the top!ViewingDirectionPicture PlaneVijay Gupta

11. ViewingDirectionProjectorsPerpendicular to picture planePoint of intersection with picture planeVijay Gupta

12. ViewingDirectionIntersections of allextreme points Vijay Gupta

13. Top ViewVijay Gupta

14. Similarly, viewing from the front with parallel projectorsFront ViewVijay Gupta

15. Top & Front Viewson opening up the pageNotice the interrelationVijay Gupta

16. Similarly, theRight Side ViewAgain notice the interrelationVijay Gupta

17. MitreThe third view can also be obtained by taking projections from the two views, using the mitre line, a line at 450Vijay Gupta

18. Two types of projections commonly used: I & III angleI-AngleIn third angle, picture planes in between the viewer & objectIn first angle, picture plane behind the objectIII-AngleVijay Gupta

19. Opening up of the box with the various views in III angleVijay Gupta

20. The relationship on plane paper of the various views in III angleIII AngleTopViewFrontViewRightViewLeft ViewVijay Gupta

21. Vijay Gupta

22. I-AngleThe relationship on plane paper of the various views in I angleFrontViewLeft ViewRightViewTopViewVijay Gupta

23. Vijay Gupta

24. MitreFrontTop ViewFront ViewVijay Gupta

25. Top ViewFrontFront ViewVijay Gupta

26. Drawing three views in III angleMitreTop ViewFrontFront ViewVijay Gupta

27. A VideoEngg_graphics.mpg

28. A demonstrationVijay GuptaGboxw31.exe

29. FrontVijay Gupta

30. FrontXXXXXXXXVijay Gupta

31. Notice that the oblique face of the cylinder appears as an ellipse in right-side view, but as lines in the front view.FrontVijay Gupta

32. Hidden Features

33. Hidden FeaturesShown by dashed lines

34. Hidden Features

35. Hidden Features

36. Hidden Features

37. Hidden Features

38. Lines and AreasProjections of lines and areas

39. Meaning of lines and areas in orthographic projectionsProjection of LinesAB

40. Projection of Lines A line may be projected in its true length

41. A line may be fore-shortened

42. A line may have a point as its projectionMeaning of Areas in Orthographic Views1. A surface in true shape2. A foreshortened surface3. A smoothly curved surface4. A combination of tangent surfaces

43. Meaning of Areas in Orthographic ViewsBBBForeshortened SurfaceSurface in True shape

44. Meaning of Areas in Orthographic ViewsCCDDCDCurved SurfaceTangent Surfaces

45. Projections of AreasSome areas are projected in true shapes, while others are distorted.Areas parallel to picture planes are in true shapesFour types of Areas1.A surface in true shape2. A foreshortened surface3. A smoothly curved surface4. A combination of tangent surfaces

46. Reading Areas A plane surface will always appear in a principal view as a line or an area

47. An plane surface that appears as a line in one view is normal to that view. It may or may not appear its true shape in the other views.

48. An plane surface that appears as a line in two of the principal viewsappears as a true shape in the third view. Reading AreasA plane surface that appears as an area in two of the principal views can not be in true shape in any view.

49. Any view that shows a plane surface as area shows it in a like shapeReading AreasAdjacent Areas lie in different planes. If two areas were in the same plane, there will not be any boundary between the two.Oblique surfaces appear as areas of like shape in all views

50. Reading Areas

51. Reading Areas

52. Reading Areas

54. Meaning of Lines in Orthographic ViewsThree possible interpretations:An edge view of a surfaceAn intersection of two surfacesA surface limit - reversal of direction of a curved surface(Surface Limit)

55. Meaning of Lines in Orthographic ViewsAn edge view of a surface

56. An intersection of two surfaces

57. A surface limit - reversal of direction of a curved surfaceMeaning of Lines in Orthographic ViewsAnother Example

58. We next illustrate how to read the orthographic drawings. This is done by interpreting the three view to ‘draw’ the represented by those view.

59. Reading Lines & AreasStart with a cuboid36271Right front corner is cut away to represent surface 12345312Top front of the upper step is removed to reconcile the slope of 23 in side view.45Front top is cut away to create a step 1267

60. Interpretation of Hidden Lines

61. Draw the pictorial views of the object whose three views are shown.

62. Draw the pictorial views of the object whose three views are shown.

77. Missing Line ExercisesIn the examples that follow, one or more lines may be missing in (only) one view. Try constructing a pictorial view to determine what line(s) are missing.

78. Missing Line ExercisesOne or more lines may be missing in (only) one view. Try constructing a pictorial view to determine what line(s) are missing.

79. Missing Line Exercises

80. Missing Line Exercises

81. Missing Line Exercises

82. Missing Line Exercises

83. Missing Line Exercises

84. Missing Line Exercises

85. Missing Line Exercises

86. Missing Line Exercises

87. Missing Line Exercises

88. Missing Line Exercises

89. Missing Line Exercises

90. Missing Line Exercises

91. Missing Line Exercises

92. Missing Line Exercises

93. Missing Line Exercises

94. Missing Line Exercises

95. Missing Line Exercises?

96. Missing Line Exercises

97. Missing Line Exercises

98. Missing Line Exercises

99. Sectional Views

100. Sectional ViewsWhenever a representation becomes confused due to too many essential hidden details that it is difficult to interpret, sectional views are employed

101. Too many hidden linesToo complicated to interpret

102. Sectional ViewsA portion of the part is cut away to reveal the interior.

103. For this purpose a cutting plane is employed. The shape of the object is clarified by distinguishing between the areas where the cutting plane actually cuts the solid material and the areas where it meets voids.

104. Wherever the cutting plane cuts the solid material, the area is hatchedSectional ViewsAThe structure of this pulley becomes clearer if we imagine the pulley is cut at the meridian plane, the material to the left of the cutting plane is removed and a projection viewing from the left is drawn.A

105. Sectional ViewsCutting PlaneThe details of the hub are now clearer.

106. Sectional ViewsA sectional view makes things much clearer.