TABLE OF CONTENTS In Chapter 1 it was stated that there are two sets of rules that apply to engineering drawing. Firstly, there are the rules that apply to the layout of a drawing and secondly the rules pertaining to the manufacture of the artefact. This chapter is concerned with the former set of rules, called the drawing layout rules . These define the projection method used to describe the artefact and how the 3D views of it can be represented on 2D paper. These will be presented in terms of first and third angle orthographic projections, sections and cutting planes, auxiliary projections as well as trimetric, dimetric, isometric and oblique projections.
The chart in Figure 2.1 shows the types of drawing projections. All engineering drawings can be divided into either pictorial projections or orthographic projections. The pictorial projections are non-specific but provide visualisation. They can be subdivided further into perspective, axonometric and oblique projections. In pictorial projections, an artefact is represented as it is seen in 3D but on 2D paper. In orthographic projections, an artefact is drawn in 2D on 2D paper. This 2D representation, rather than a 3D representation, makes life very much simpler and reduces confusion. In this 2D case, the representation will lead to a specification that can be defined by laws. The word ortho means correct and the word graphic means drawing. Thus, orthographic means a correct drawing which prevents confusion and therefore can be a true specification which, because orthographic projections are...
