Page 45 - CITS - ED - Mechanical

ENGINEERING DRAWING - CITS

All the four quadrants have one HP and one VP formation. As per convention in mathematics, the quadrants are
numbered as 1 , 2 , 3 and 4 . These four quadrants are called four dihedral angles, namely 1 angle, 2 angle,
nd
st
nd
rd
th
st
3 angle and 4 angle.
rd
th
To draw two views of an object, we assume that the object is placed in any one of the quadrant/angles, 1st angle &
3rd angle Fig 8a, 9a and its plan and elevation projected to the respective planes. Now tomake it possible to draw
the two views (Plan & elevation) in one plane i.e the plane of the drawing paper, the horizontal plane is assumed
to be unfolded in clockwise direction through 90° Fig 8b & 9b. We proceed this way, when the views are made.
When the object is placed in the 2 or fourth quadrant the plan and elevation will get super imposed (one up on
nd
the other) Fig 10a & b. Due to this reason the 2 and 4 angle are not used for making engineering drawings as
nd
th
the three dimensions cannot be easily identified. Hence for representing the three dimension of the object, we
assume the object is placed either in 1 angle and in 3 angle (Fig 11 & 12) respectively
st
rd
Fig 7 Fig 8

Fig 9 Fig 10

Fig 12
Fig 11

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CITS : Engineering Drawing (Mechanical) - Exercise 4