Engineering Drawing Orthographic Projection

    Engineering drawing is two-dimensional depiction of various phases of actual objects. To make engineering drawings meaningful and executable, different phases of an object are depicted in two-dimension and placed in a particular way using technique of Projection. We need to know following terms before reading about Orthographic Projection ;

What are Projections, Projection Plane, Projection Lines  in Engineering Drawing ?

           

         As discussed above that ED is two-dimensional depiction of various phases of actual object, a phase of object is projected on a plane using imaginary lines and the two-dimensional figure then formed is called Projection or Graphical Projection of object. Imaginary lines, known as Projection Lines, are drawn from various points on contour of the object and are projected to meet at a plane known as Projection Plane.

What is Orthographic Projection in Engineering Drawing ?

        Orthographic Projection, also known as Multi-view Projection, is universally accepted way of depiction of shapes of an object through two-dimensional figures on a plane. Projection Lines are parallel to each other and are orthogonal to plane of projection. Two types of orthographic projections namely, i) First Angle Projection and ii) Third Angle Projection have been explained below ;

First Angle Orthographic Projection ;

      In first angle projection, object is placed in first quadrant so that the Vertical Plane is behind of the object and Horizontal Plane is below the object.

First Angle Projection Method ;

      In first angle projection, projections of an object are drawn in following ways ;

         a)      Top View of object is drawn below Front View.

         b)      Right Side View is drawn towards left side of Front View.

         c)       Bottom View of object is drawn above Front View.  

         d)      Left Side View is drawn towards right side of Front View.

Third Angle Orthographic Projection ;

    In third angle projection, object is placed in third quadrant so that the Vertical Plane is in front of the object and Horizontal Plane is above the object.

Third Angle Projection Method ;

   In third angle projection, projections of an object are drawn, normally, in following ways ;

        a)      Top View of object is drawn above Front View.

        b)      Right Side View is drawn towards right side of Front View.

        c)       Bottom View of object is drawn below Front View.

        d)    Left Side View is drawn towards left side of Front View.

         
     
        
                 Symbols of first angle projection or third angle projection are drawn in right bottom or top corner along-with other descriptions like tolerance, material, name of organization, etc. in engineering drawings, so that engineer before reading drawing will know that the drawing is made using first angle projection or third angle projection.

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