CHAPTER 5DRAFTING: PROJECTIONSAND SKETCHINGThis chapter deals with the theory ofprojections and methods of preparing projectiondrawings. By applying basic geometric con-struction (described in the preceding chapter) tothe various projection methods, you should beable to clearly represent any given object orstructure on paper. Although the methodsdiscussed here are basic to all drawings, they areeasily adapted to construction drawings. Thischapter also covers various techniques of freehandsketching. You will learn how to prepare quicksketches to convey or develop your ideas.Every object or structure you draw has length,width, and depth, regardless of its size. However,you must draw the object or structure on paper,which is a flat two-dimensional plane. To showthe three dimensions by lines alone, you must useeither a system of related views or a singlepictorial projection. You must be able to showclearly the shape of the object, give the exact sizeof each part, and provide necessary informationfor constructing the object.In theory, projection is done by extending linesof sight (called projection lines) from the eye ofthe observer, through lines and points of anobject being viewed, to the plane of projection.PARALLEL PROJECTIONTo satisfy requirements for preparing single-or multi-view drawings, you may use two maintypes of projection: PARALLEL and PER-SPECTIVE (fig. 5-1). PARALLEL projectionFigure 5-1.—Classification of major projections.5 - 1
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