Engineering Drawing

Engineering Drawing is the universal language of engineers. The idea is drawn on sheet by using point, line and other drawing entities to give complete information or complete detail about idea. Engineering drawings are those drawings which are used in shop floor to improve the productivity. 

The sound  knowledge of the engineering drawing is essential to all engineering students. Engineering Drawing is difficult to understand for first year student of engineering. 

Introduction to Orthographic Projection

Projection

A projection is defined as an image or a drawing of an object made on a plane. All drawings used in the field of engineering are based on the principles of projection. Projections can be classified on the basis of the lines of sight and the positions of planes on which the drawing is made.

The lines of sight are popularly called projectors and the planes on which the drawings are made are called planes of projection.

Orthographic Projection

Orthographic is also called parallel line projection, the projectors are parallel to each other and also perpendicular to the plane.

Imagine that an observer looks at the object from the infinite distance, so the rays of sight is parallel to each other and perpendicular to the surface of the object. The view obtained on the Vertical plane (VP) is called Front View (FV) of the object.

Let us further assume that plane marked Horizontal Plane (HP). An observer looks the object in such a ways that the rays of sight is parallel to each other and perpendicular to HP, the view obtained on HP is called Top View (TV).

If observer looks the object in such a way that the rays of sight is parallel to each other and perpendicular to Profile Plane (PP), the view obtained on PP is called Side View (SV).

Figure 1

    The object is place above the HP and in-front of VP shown in figure 1. The front view obtained
    on VP, top view on HP and side view on PP are shown in figure 1.

    The views obtained in orthographic projection are two dimensional, so two or more than two
    views are required to describe the object.

   

    Figure 2 shows the Front View, Top View and Side View of the object on Vertical plane,
    Horizontal plane and Profile plane respectively. 

Figure 2 

Figure 3 

Figure 4

The horizontal plane and profile plane are rotates with respect to vertical plane. The direction of rotation is shown in figure 2. The final drawing is shown in figure 4.

Types of Orthographic Projection

First Angle

In first angle of projection the object is place above the horizontal plane and infront of vertical plane. The object lies between the vertical plane and observer.

The front view of the object draw above the reference line and top view of the object draw below the reference line.

Second Angle

In second angle of projection the object is place behind the vertical plane and above the horizontal plane. The vertical plane lies between object and observer.

Both front view and top view of the object lies above the reference line.

Third Angle

In third angle of projection the object is place below the horizontal plane and behind the plane vertical. The vertical plane lies between object and observer.

The front view of the object draw below the reference line and top view of the object draw above the reference line.

Fourth Angle

In fourth angle of projection the object is place infront of the vertical plane and below the horizontal plane. The object lies between vertical plane and observer.

Both front view and top view of the object lies below the reference line

Symbol of Projection