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CHAPTER 8 Multiview Drawings 377 Media Chapter Multiview Drawings 8 OBJECTIVES As lines, so loves oblique, may well After completing this chapter, you will be able to: Themselves in every angle greet; But ours, so truly parallel, 1. Explain orthographic and multiview projection. 2. Identify frontal, horizontal, and profile planes. Though infinite, can never meet. 3. Identify the six principal views and the three space Andrew Marvell dimensions. 4. Apply standard line practices to multiview drawings. 5. Create a multiview drawing using hand tools or CAD. 6. Identify normal, inclined, and oblique planes in multiview drawings. 7. Represent lines, curves, surfaces, holes, fillets, rounds, chamfers, runouts, and ellipses in multiview drawings. 8. Apply visualization by solids and surfaces to multiview drawings. 9. Explain the importance of multiview drawings. 10. Identify limiting elements, hidden features, and intersections of two planes in multiview drawings. INTRODUCTION Chapter 8 introduces the theory, techniques, and standards of multiview drawings, which are a standard method for representing engineering designs. The chapter describes how to create one-, two-, and three-view drawings with traditional tools and CAD. Also described are standard practices for representing edges, curves, holes, tangencies, and fillets and rounds. The foundation of multiview draw- ings is orthographic projection, based on parallel lines of sight and mutually perpendicular views. I 375 Figure 8.1 Projection Methods Projections Projection techniques developed along two lines: parallel and perspective. Perspective or Central Parallel Projections Projections Orthographic Linear Aerial Oblique Projections Perspectives Perspectives Projections Axonometric Multiview Projections Projections Half Depth Cabinet One-Point Projection Perspective q g b Isometric a oc a = b = c oq = or = og Full Aerial Perspective Depth Object features appear r Two-Point Cavalier less focused at a distance g Perspective Projection q b Dimetric ≠ a oc a = b c oq = or ≠ og Depth Varies Three-point General r Perspective g Projection q b Trimetric ≠ ≠ a o c a b c The Attributes of Each Projection Method oq ≠ or ≠ og One principal Lines of plane parallel r Projection Method Application Sight to plane of projection Linear Perspective Converging; Sometimes Single view T -One-Point inclined to pictorial -Two-Point plane of -Three-Point projection T Oblique Projection Parallel; Always Single view -Cavalier inclined to pictorial F -Cabinet plane of RS FRS -General projection Third-angle projection Orthographic Projection F Axonometric Parallel; Never Single view RS -Isometric normal to pictorial -Dimetric plane of RS F -Trimetric projection Multiview Projection Parallel; For all Multiview T -Third Angle normal to principal drawings T (preferrred) plane of views -First Angle projection First-angle projection 8.1 PROJECTION THEORY methods are based on projection theory, which has taken Engineering and technical graphics are dependent on pro- many years to evolve the rules used today. jection methods. The two projection methods primarily Projection theory comprises the principles used to used are perspective and parallel. (Figure 8.1) Both represent graphically 3-D objects and structures on 2-D CHAPTER 8 Multiview Drawings 377 media. An example of one of the methods developed to All projection theory is based on two variables: line of accomplish this task is shown in Figure 8.2, which is a sight and plane of projection. These variables are de- pictorial drawing with shades and shadows to give the scribed briefly in the following paragraphs. impression of three dimensions. 8.1.1 Line of Sight (LOS) Drawing more than one face of an object by rotating the object relative to your line of sight helps in understanding the 3-D form. (Figure 8.3) A line of sight (LOS) is an imaginary ray of light between an observer’s eye and an object. In perspective projection, all lines of sight start at a single point (Figure 8.4); in parallel projection, all lines of sight are parallel (Figure 8.5). 8.1.2 Plane of Projection A plane of projection (i.e., an image or picture plane) is an imaginary flat plane upon which the image created by the lines of sight is projected. The image is produced by connecting the points where the lines of sight pierce the Figure 8.2 Pictorial Illustration projection plane. (See Figure 8.5.) In effect, the 3-D ob- This is a computer-generated pictorial illustration with shades ject is transformed into a 2-D representation (also called and shadows. These rendering techniques help enhance the 3-D a projection). The paper or computer screen on which a quality of the image. (Courtesy of SDRC.) sketch or drawing is created is a plane of projection. Parallel lines of sight OO rthographicRTH O GR APH IC R evolvedREV OLVED TTIPPEDipped forw FO ardR WA RD (Plane Paperof projection) Figure 8.3 Changing Viewpoint Changing the position of the object relative to the line of sight creates different views of the same object. 378 PART 2 Fundamentals of Technical Graphics Nonparallel lines of sight radiating from a point View picture of planeobject projected onto Picture plane (paper or com puter screen) Observer (Station point) One viewpoint Figure 8.4 Perspective Projection Radiating lines of sight produce a perspective projection. Parallel lines of sight View picture of planeobject projected onto Picture plane (paper or com puter screen) Observer (Station point) Infinite viewpoint Figure 8.5 Parallel Projection Parallel lines of sight produce a parallel projection. 8.1.3 Parallel versus Perspective Projection requires that the object be positioned at infinity and If the distance from the observer to the object is infinite viewed from multiple points on an imaginary line paral- (or essentially so), then the projectors (i.e., projection lel to the object. If the distance from the observer to the lines) are parallel and the drawing is classified as a paral- object is finite, then the projectors are not parallel and the lel projection. (See Figure 8.5.) Parallel projection drawing is classified as a perspective projection. (See CHAPTER 8 Multiview Drawings 379 Figure 8.4.) Perspective projection requires that the ob- show all three dimensions of an object in one view or ject be positioned at a finite distance and viewed from a multiviews that show only two dimensions of an object single point (station point). in a single view. (Figure 8.6) Perspective projections mimic what the human eye sees; however, perspective drawings are difficult to cre- ate. Parallel projections are less realistic, but they are 8.2 MULTIVIEW PROJECTION PLANES easier to draw. This chapter will focus on parallel projec- tion. Perspective drawings are covered in Chapter 10. Multiview projection is an orthographic projection for Orthographic projection is a parallel projection which the object is behind the plane of projection, and the technique in which the plane of projection is positioned object is oriented such that only two of its dimensions are between the observer and the object and is perpendicular shown. (Figure 8.7) As the parallel lines of sight pierce to the parallel lines of sight. The orthographic projection the projection plane, the features of the part are outlined. technique can produce either pictorial drawings that Multiview drawings employ multiview projection techniques. In multiview drawings, generally three views of an object are drawn, and the features and dimensions in each view accurately represent those of the object. Each view is a 2-D flat image, as shown in Figure 8.8. The views are defined according to the positions of the planes of projection with respect to the object. 8.2.1 Frontal Plane of Projection Isometric Oblique Multiview The front view of an object shows the width and height Figure 8.6 Parallel Projection dimensions. The views in Figures 8.7 and 8.8 are front Parallel projection techniques can be used to create multiview views. The frontal plane of projection is the plane onto or pictorial drawings. which the front view of a multiview drawing is projected. Plane of Plane of projection projection (frontal) (frontal) Depth Lines of sight perpendicular to plane Front of projection Projectors perpendicular to view plane Object’s depth is not represented (A) (B) Figure 8.7 Orthographic Projection Orthographic projection is used to create this front multiview drawing by projecting details onto a projection plane that is parallel to the view of the object selected as the front. 380 PART 2 Fundamentals of Technical Graphics Industry Application CAD and Stereolithography Speed Solenoid Design When Peter Paul Electronics faced the need to quickly re- cause the sleeve sits inside the coil, which is the heart of design a humidifier solenoid valve, Senior Design Engi- the solenoid valve. In addition, a plunger that causes air neer Thomas J. Pellegatto naturally turned his CAD-KEY- or fluid to flow in the valve rises inside the sleeve. based system loose on the physical parameters of the According to Pellegatto, the simplest method for new valve. But that wasn’t enough. The design required reducing cost and complexity of the critical sleeve lower-cost manufacturing technology as well as dimen- assembly was to use the coil’s bobbin to replace the sional and mechanical design changes. sleeve and house the plunger. Working directly with engi- Existing valves from the company feature an all-steel neers at DuPont, designers selected a thermoplastic sleeve, consisting of a flange nut, tube, and end stop, all named Rynite to eliminate misalignment and the need for of which are staked together for welding. A weld bead se- welding the new assembly. The CAD system fed Peter cures the end stop to the tube at the top edge and joins Paul’s internal model shop with the data to develop bob- the tube and threaded portion of the flange nut at the bot- bin prototypes from the thermoplastic.
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