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# 14773 chapter 07

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### 14773 chapter 07

1. 1. Mechanical Sciences-I<br />Chapter 7: Orthographic Projections<br />
2. 2. Introduction to Orthographic Projections<br />Introducing Orthographic Projections as the language of engineering designers <br />
3. 3. Orthographic Projections<br /><ul><li>Orthographic projections are an engineer’s language for conveying the shape and size information about the products he designs.
4. 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. 5. The parallel rays that are used for constructing the views are called projectors.</li></ul>Vijay Gupta<br />
6. 6. Orthographic Projections<br /><ul><li>The 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. 7. The intersections of the projectors with the picture plane are the projections of the points from which the projectors emanate.
8. 8. The points are joined to obtain the views.</li></ul>Vijay Gupta<br />
9. 9. We consider here the development of the orthographic views of a simple object.<br />Object<br />Vijay Gupta<br />
10. 10. For the Top view we view from the top!<br />Viewing<br />Direction<br />Picture Plane<br />Vijay Gupta<br />
11. 11. Viewing<br />Direction<br />Projectors<br />Perpendicular to picture plane<br />Point of intersection with picture plane<br /><br />Vijay Gupta<br />
12. 12. Viewing<br />Direction<br /><br /><br /><br /><br />Intersections of all<br />extreme points <br />Vijay Gupta<br />
13. 13. Top View<br />Vijay Gupta<br />
14. 14. Similarly, viewing from the front with parallel projectors<br />Front View<br />Vijay Gupta<br />
15. 15. Top & Front Views<br />on opening up the page<br />Notice the interrelation<br />Vijay Gupta<br />
16. 16. Similarly, the<br />Right Side View<br />Again notice the interrelation<br />Vijay Gupta<br />
17. 17. Mitre<br />The third view can also be obtained by taking projections from the two views, using the mitre line, a line at 450<br />Vijay Gupta<br />
18. 18. Two types of projections commonly used: I & III angle<br />I-Angle<br />In third angle, picture planes in between the viewer & object<br />In first angle, picture plane behind the object<br />III-Angle<br />Vijay Gupta<br />
19. 19. Opening up of the box with the various views in III angle<br />Vijay Gupta<br />
20. 20. The relationship on plane paper of the various views in III angle<br />III Angle<br />Top<br />View<br />Front<br />View<br />Right<br />View<br />Left View<br />Vijay Gupta<br />
21. 21. Vijay Gupta<br />
22. 22. I-Angle<br />The relationship on plane paper of the various views in I angle<br />Front<br />View<br />Left View<br />Right<br />View<br />Top<br />View<br />Vijay Gupta<br />
23. 23. Vijay Gupta<br />
24. 24. Mitre<br />Front<br />Top View<br />Front View<br />Vijay Gupta<br />
25. 25. Top View<br />Front<br />Front View<br />Vijay Gupta<br />
26. 26. Drawing three views in III angle<br />Mitre<br />Top View<br />Front<br />Front View<br />Vijay Gupta<br />
27. 27. A Video<br />Engg_graphics.mpg<br />
28. 28. A demonstration<br />Vijay Gupta<br />Gboxw31.exe<br />
29. 29. Front<br />Vijay Gupta<br />
30. 30. Front<br />X<br />X<br />X<br />X<br />X<br />X<br />X<br />X<br />Vijay Gupta<br />
31. 31. Notice that the oblique face of the cylinder appears as an ellipse in right-side view, but as lines in the front view.<br />Front<br />Vijay Gupta<br />
32. 32. Hidden Features<br />
33. 33. Hidden Features<br />Shown by dashed lines<br />
34. 34. Hidden Features<br />
35. 35. Hidden Features<br />
36. 36. Hidden Features<br />
37. 37. Hidden Features<br />
38. 38. Lines and Areas<br /><ul><li>Projections of lines and areas
39. 39. Meaning of lines and areas in orthographic projections</li></li></ul><li>Projection of Lines<br />A<br />B<br />
40. 40. Projection of Lines<br /><ul><li> A line may be projected in its true length
41. 41. A line may be fore-shortened
42. 42. A line may have a point as its projection</li></li></ul><li>Meaning of Areas in Orthographic Views<br />1. A surface in true shape<br />2. A foreshortened surface<br />3. A smoothly curved surface<br />4. A combination of tangent surfaces<br />
43. 43. Meaning of Areas in Orthographic Views<br />B<br />B<br />B<br />Foreshortened Surface<br />Surface in True shape<br />
44. 44. Meaning of Areas in Orthographic Views<br />C<br />C<br />D<br />D<br />C<br />D<br />Curved Surface<br />Tangent Surfaces<br />
45. 45. Projections of Areas<br />Some areas are projected in true shapes, while others are distorted.<br />Areas parallel to picture planes are in true shapes<br />Four types of Areas<br />1.A surface in true shape<br />2. A foreshortened surface<br />3. A smoothly curved surface<br />4. A combination of tangent surfaces<br />
46. 46. Reading Areas<br /><ul><li> A plane surface will always appear in a principal view as a line or an area
47. 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. 48. An plane surface that appears as a line in two of the principal viewsappears as a true shape in the third view. </li></li></ul><li>Reading Areas<br /><ul><li>A plane surface that appears as an area in two of the principal views can not be in true shape in any view.
49. 49. Any view that shows a plane surface as area shows it in a like shape</li></li></ul><li>Reading Areas<br />Adjacent Areas lie in different planes. If two areas were in the same plane, there will not be any boundary between the two.<br />Oblique surfaces appear as areas of like shape in all views<br />
53. 53.
54. 54. Meaning of Lines in Orthographic Views<br />Three possible interpretations:<br />An edge view of a surface<br />An intersection of two surfaces<br />A surface limit - reversal of direction of a curved surface<br />(Surface Limit)<br />
55. 55. Meaning of Lines in Orthographic Views<br /><ul><li>An edge view of a surface
56. 56. An intersection of two surfaces
57. 57. A surface limit - reversal of direction of a curved surface</li></li></ul><li>Meaning of Lines in Orthographic Views<br />Another Example<br />
58. 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.<br />
59. 59. Reading Lines & Areas<br />Start with a cuboid<br />3<br />6<br />2<br />7<br />1<br />Right front corner is cut away to represent surface 12345<br />3<br />1<br />2<br />Top front of the upper step is removed to reconcile the slope of 23 in side view.<br />4<br />5<br />Front top is cut away to create a step 1267<br />
60. 60. Interpretation of Hidden Lines<br />
61. 61. Draw the pictorial views of the object whose three views are shown.<br />
62. 62. Draw the pictorial views of the object whose three views are shown.<br />
63. 63.
64. 64.
65. 65.
66. 66.
67. 67.
68. 68.
69. 69.
70. 70.
71. 71.
72. 72.
73. 73.
74. 74.
75. 75.
76. 76.
77. 77. Missing Line Exercises<br />In 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.<br />
78. 78. Missing Line Exercises<br />One or more lines may be missing in (only) one view. Try constructing a pictorial view to determine what line(s) are missing. <br />
79. 79. Missing Line Exercises<br />
80. 80. Missing Line Exercises<br />
81. 81. Missing Line Exercises<br />
82. 82. Missing Line Exercises<br />
83. 83. Missing Line Exercises<br />
84. 84. Missing Line Exercises<br />
85. 85. Missing Line Exercises<br />
86. 86. Missing Line Exercises<br />
87. 87. Missing Line Exercises<br />
88. 88. Missing Line Exercises<br />
89. 89. Missing Line Exercises<br />
90. 90. Missing Line Exercises<br />
91. 91. Missing Line Exercises<br />
92. 92. Missing Line Exercises<br />
93. 93. Missing Line Exercises<br />
94. 94. Missing Line Exercises<br />
95. 95. Missing Line Exercises<br />?<br />
96. 96. Missing Line Exercises<br />
97. 97. Missing Line Exercises<br />
98. 98. Missing Line Exercises<br />
99. 99. Sectional Views<br />
100. 100. Sectional Views<br />Whenever a representation becomes confused due to too many essential hidden details that it is difficult to interpret, sectional views are employed<br />
101. 101. Too many hidden lines<br />Too complicated to interpret<br />
102. 102. Sectional Views<br /><ul><li>A portion of the part is cut away to reveal the interior.
103. 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. 104. Wherever the cutting plane cuts the solid material, the area is hatched</li></li></ul><li>Sectional Views<br />A<br />The 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.<br />A<br />
105. 105. Sectional Views<br />Cutting Plane<br />The details of the hub are now clearer.<br />
106. 106. Sectional Views<br />A sectional view makes things much clearer.<br />
107. 107. Sectional Views<br />
108. 108. Sectional Views<br />This does not differentiate cut and uncut portions<br />Note that the cutting plane line is long dash – two short dashes line<br />
109. 109. Sectional Views<br />Hatch the solid portions which are exposed freshly by the cutting plane<br />These areas not hatched because the cutting plane does not cut any material here. These represent holes.<br />
110. 110. Sectional Views<br />5/4 ream<br />Clarify the view using sections.<br />
111. 111. Sectional Practices<br />In the following slides we show some sectioning practices. The principle involved in these practices is to reduce the drawing effort as much as possible while maintaining clarity as much as possible. <br /><ul><li>Try reducing the number of views required.
112. 112. Draw as few hidden lines as possible. Use a variety of sections as required.</li></li></ul><li>Offset Sections<br />Note that the sectioning plane is offset to bring out both the hidden features in one view<br />
113. 113. Full Sections<br />
114. 114. Half Sections<br />In many symmetrical objects one can show the internal & the external feature in the same view by considering a plane which cuts only one half the object.<br />