1. Orthogonal Projection and Multiview Representation
Chapter 10
Orthogonal Projection and
Multiview Representation

2. Objectives Discuss the principles of orthogonal projection
Show how orthogonal projection is used to create multiple views of an object for formal engineering drawing

3. Objectives (cont’d.)
Explain why orthogonal projection is necessary to represent objects in formal engineering drawing
Create a multiview drawing from a 3-D object

4. Introduction
Best way to communicate appearance of an object is to show its image
Images in engineering drawings must be interpreted the same way
Enough views must be provided so that all features can be clearly seen and accurately measured

5. A More Precise Way to Communicate Your Ideas
Products must be represented so that there is no misinterpretation
How would you communicate what you want built to those who build it?
How would you ensure that different people interpret and build the product the same way every time?

6. Problems with Pictorials
FIGURE Distortion of internal lengths in pictorials. These different lengths on the same object represent the same length, which is the diameter of the holes in the cube.
FIGURE Distortion of true lengths and angles in pictorial presentations.

7. Viewing Planes
When you visualize an object, its appearance changes based on viewing direction
Viewing plane is transparent plane fixed in space between you and the object
2-D image of 3-D object
Depends on viewing angle

8. Orthogonal Projection
FIGURE Using orthogonal projection to create an image of an object on a viewing plane. The object in (a) is in front of the viewing plane. The object in (b) is behind the viewing plane. In either case, the projection lines are perpendicular to the viewing plane, as shown in (c).

9. A Distorted Reality
FIGURE The top photograph was taken from up close. The bottom photo was taken from a long distance and
enlarged so feature sizes could
be compared. Can you see the
lack of perspective in the long-distance photo?

10. Choice of Viewing Planes
FIGURE A single view of a part may have many different Interpretations.

11. Choice of Viewing Planes (cont’d.)
FIGURE Two viewing
planes that are orthogonal to
the first (front) viewing plane
(a) can be unfolded (b) to present
the images on a single plane
(c). The imaginary hinges for
the two viewing planes are at the
intersections of these planes
with the front viewing plane.

12. Size and Alignment
FIGURE Viewing planes completely unfolded showing proper size, location, and orientation of the images on a single plane.

13. The Glass Box
FIGURE Viewing an engineered part through a glass box (a) that opens (b) to present the images on a single plane (c).

14. Standard Views Six standard views (six principal views) Front Top
Left side
Right side
Rear
Bottom

15. The Preferred Configuration
FIGURE The preferred
presentation configuration
showing the front, top, and
right-side views of an object.
Other views are added only
when necessary to show features that cannot be defined in the preferred configuration.

16. The Necessary Details Hidden lines and centerlines
Hidden lines are obscured features or edges
Denoted as equally spaced dashed lines
Centerlines identify centers of circular holes
Centermarks are end views of centerlines
Identified by right-angle cross

17. The Necessary Views
FIGURE For a part with a constant but significant thickness,
including a second view is a good idea to emphasize the 3-D nature of the part.

18. The Necessary Views (cont’d.)
FIGURE Different interpretations of a drawing with two views. A third view is necessary.

19. Hidden Lines versus More Views
FIGURE Hidden and internal features on a part. Using hidden lines makes the left side and bottom views optional.

20. Hidden Lines versus More Views (cont’d.)
FIGURE Overuse of hidden lines causes confusion. Exercise judgment. It might be better to create another view, such as a rear view in this case.

21. First-Angle Projection versus Third-Angle Projection
FIGURE Viewing an
object in front of opaque panels
for first-angle projection. The
images are projected onto the
panels (a), which open (b) to
present the images on a single
plane (c).

22. First-Angle Projection versus Third-Angle Projection (cont’d.)
FIGURE The six standard views, using first-angle projection, presented on a single sheet.

23. First-Angle Projection versus Third-Angle Projection (cont’d.)
FIGURE Drawing interpretation using first-angle or third-angle projection may lead to different parts.

24. Strategies for Creating Multiviews from Pictorials
Step 1: On pictorial, specify viewing directions and create a sheet with areas reserved for appropriate orthogonal views
Step 2: Find the maximum size of the object in each of the three directions and in each view, sketch the limits of a rectilinear box

25. Point Tracking Step 3: Define an anchor point
Step 4: Locate a vertex adjacent to the anchor point and draw that edge
Step 5: Successively locate other vertices and draw the edges between those vertices
Step 6: Convert hidden lines

26. Point Tracking (cont’d.)
Step 7: Add internal features
Step 8: Check model validity

27. Edge Tracking Step 3: Define an anchor edge
Step 4: Locate an edge adjacent to the anchor point, and draw that edge
Step 5: Successively locate other adjacent edges
Steps 1, 2, 6, 7, 8 same as point tracking

28. Surface Tracking Step 3: Define an anchor surface
Step 4: Locate a surface adjacent to the anchor surface and draw its boundary
Step 5: Successively locate other adjacent surfaces and draw those boundaries
Steps 1, 2, 6, 7, 8 same as point and edge tracking

29. Surface Tracking (cont’d.)
FIGURE Considering the existence of oblique surfaces, how would you create a multiview drawing of this object?

30. Surface Tracking (cont’d.)
FIGURE Define the foundation space, viewing directions, and anchor surface.

31. Surface Tracking (cont’d.)
FIGURE Continue the process of surface location for the noninclined surfaces. Since the oblique surfaces do not intersect, their boundaries are automatically formed by the normal surfaces.

32. Breaking the Rules—and Why It Is Good to Break Them Sometimes
Threaded parts
FIGURE The schematic representation of an externally threaded part. The note specifies the metric size of the thread.

33. Features with Small Radii
FIGURE The representation of small radii on a part.

34. Small Cutouts on Curved Surfaces
FIGURE The true projection and an acceptable shortcut for small holes and slots on a curved surface. The shortcuts should not be used for large holes and slots because the geometric inaccuracies would be too obvious.

35. Small Intersections with Curved Surfaces
FIGURE The true projection and an acceptable shortcut for small protrusions from a curved surface. The shortcuts should not be used for large protrusions because the geometric inaccuracies would be too obvious.

36. Symmetrical Features
FIGURE The true projection and an acceptable shortcut for an object with prominent symmetry. This property is emphasized by the use of a projected view that is modified to appear symmetrical.

37. Representation of Welds
FIGURE The acceptable presentation of two parts that are welded together to make a single part. The note specifies the size and location of the welds.

38. When Six Views Are Not Enough
Features at odd angles
Internal features
FIGURE An object such as this one cannot be fully described by the six standard views.
FIGURE An object with internal features such as this one cannot be fully described by the six standard views.

39. Considerations for 3-D Modeling
Pictorials and multiview drawings easily created from solids model
Advantage: speed and accuracy in creating orthogonal views
Disadvantage: dependence on software

40. Summary
Introduced orthogonal projection and the use of the standard views of an object
Discussed the rules for view creation, orientation, scale, and alignment
Used hidden lines for additional emphasis of certain features on the object
Used extra views as necessary for completing description of features