Orthographic Projections

Lines are used to construct a drawing. Various type of lines are used to construct meaningful drawings. Each line in a drawing is used to convey some specific information.  The types of lines generally used in engineerign drawing is shown in Table-1.

Table -1. Types of lines generally used in drawings

 

All visible edges are to be represented by visible lines. This includes the boundary of the object and  intersection between two planes. All hidden edges and features should be represented by dashed lines.  Figure 1 shows the orthographic front view  (line of sight in the direction of arrow)of an object. The external boundary of the object is a rectangle and is shown by visible lines.  In Figure-1(a), the step part of the object is hidden and hence shown as dashed lines while for the position of the object shown in figure-1(b) , the step part is directly visible and hence shown by the two solid lines.

Figure 1  shows the pictorial view and front view of the object when the middle stepped region is (a) hidden and (b) visible.