Orthographic drawing is imagined as enclosing the object in a transparent box where each surface of the box represents a projection plane. This is also called as Third Angle Projection. Unfolding the box provides the standard views used in orthographic projections as shown in figures – 2 & 3. The symbol to be placed on the drawing is shown in figure – 4
With first angle projection the object is drawn as if the object is placed on each side of the glass box that is as if the object is projected onto the drawing surface. Figure – 5 & 6) The symbol to be placed on the drawing to show First Angle Projection is shown in figure – 7
In developing the needed views the object is normally viewed from six sides / directions. It does not mean that all these views need to be drawn. Care should be taken to select only those views required to give a shape and description of the object completely without repeat drawings.
Orthographic projection drawings are clearly an abstraction of reality and use specific conventions to delineate space and materials. Unlike other forms of drawing, orthographic projection drawings require adherence to conventions, proportional scale, and accuracy of line; these design drawings are highly standardized so that they carry universal meaning. Therefore, items such as walls, doors, windows, property boundaries, references to other drawings and other items are represented by very specific graphic symbols or combinations of lines. Graphic symbols used for references and notes. Lines are used to represent surface features of the object. Dashed lines are used for features that are not visible or behind the object surface from the given view. Creating multi view drawings using orthographic projections is fairly easy. After the front view is drawn to scale, other views can be constructed with almost no further measurements. All width dimensions can be projected from the front view to produce top and bottom view and all height dimensions can be projected to produce side views. Only the depth needs to be measured either on top or side view and then transferred to the other by means of a 45 degree line.
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