Orthographic Projection

1. Orthographic Projection • Ortho -- perpendicular • The system of drawing views of an object by projecting points perpendicularly onto projection planes. • Projection lines represent line of sight • Line of sight perpendicular to projection plane • Multiviews • two-dimensional views of an object projected upon two or more planes of projection using orthographic projection techniques.

2. Orthographic projection

3. Multiview drawing of an object

4. Glass Box Model • Place object in a glass box so the sides of the glass box are parallel to major surfaces of the object. • Third-Angle projection - used in the US: • Top view directly above the front view • Right-side view to the right of front view • Faces of the glass box serve as planes of projection • Cut glass box along edges and unfold to obtain multiviews

5. Glass Box Unfolding

6. Orthographic Views • Common projection planes (aka principal projection planes) • frontal F  front view • horizontal H  top view • profile P  right-side view • Cut and open the glass box to get principal orthographic views • Other views: • bottom, rear, left-side

7. Dimensions • Dimensions necessary to define object: • Height H -- FV & RV • Width -- TV & FV • Depth -- TV & RV • Alignment of views • align corresponding dimensions • Represent hidden edges by dashed lines

8. Three space dimensions

9. Alignment of views

10. Selecting the Front View • Represents the most natural position of use • Provides the best shape description or most characteristic contours • Has longest dimension • Has fewest hidden features

11. Good orientation

12. Object suspended in a glass box, producing the six principal views

13. Unfolding the glass box to produce a six-view drawing

14. Most descriptive views

15. Types of Lines • Object lines (visible lines) • solid lines • represent visible surfaces or edges of the object • Hidden lines • dashed lines • invisible edges of the object • Centerlines • long-short dashes • used to show centers of circles and arcs • Others: extension, dimension, phantom, section, cutting-plane

16. Hidden features

17. Tangent partial cylinder

18. Nontangent partial cylinder

19. Line Precedence • When one type of line falls in line with a different line type, draw the line that is most important based on precedence: • Object lines take precedence over hidden lines and centerlines. • Hidden lines take precedence over centerlines. • In sectioning, cutting plane lines take precedence over center lines.

20. Representing Planes • Normal Plane • parallel to a principal projection plane • can be seen in only one view as True Size • Inclined Plane • tilted with respect to two principal proj planes • seen in two views; not true size • Oblique Plane • tilted with respect to all principal proj planes • seen in three views; not true size

21. Fundamental views of surfaces

22. Rule of configuration of planes

23. Surface labeling

24. Numbering the isometric pictorial and the multiviews to help visualize an object

25. Orthographic Views in AutoCAD • Group entities together into LAYERS. Use the layer manager to create layers. • Object lines • hidden lines • section lines and hatching • text and dimensions • title border • Create rectangles for front, top, and right-side views • use 3rd angle projection • appropriate spacing between views

26. OV with AutoCAD • Use horizontal construction lines to locate height dimensions common between FV and RV. • Use vertical construction lines for width dimensions in FV and TV. • Use a 45-degree projection line (miter line) to transfer depth dimensions between TV and RV. • Locate and plot projections of normal planes first, then inclined and oblique planes. Use solid lines for all visible object lines.

27. OV with AutoCAD • Locate all hidden edges; use dashed lines. • Locate centerlines of all circles and arcs. • Check visibility of lines following precedence rules. • Add dimensions and text. • Import title block.