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ENGINEERING DRAWING - CITS

Fig 4 Fig 5

The length of non-isometric lines will not follow the scale used for isometric lines. To prove this point consider the
non-isometric lines AB or BC. The true length of both AB and BC is 5 cm while BC will be longer. Because of this
reason non-isometric lines are drawn first by locating their starting and end points on isometric lines.
To locate the end points and to draw the non-isometric lines two methods are employed. They are
– Box method
– Off-set method
Box method: The object is assumed to be inside a rectangular box. Starting and end points are located and
marked. By joining the points isometric view is drawn.
Off-set method: This method is most suited for the objects consisting of number of planes at a number of different
angles.

These methods are not only useful for isometric views involving non-isometric lines but also for the
isometric views involving isometric lines.

Box method of drawing a pyramid
Example
Draw an isometric view for the triangular pyramid shown in Fig 6 using a box method.

Fig 6

– Construct a rectangular box to the overall size of the pyramid (Fig 7a)

– Mark the distances ad and be from the plan of Fig 7b in the base of the box.
– Mark the distances kg and dh on the top face of box. (Fig 7c)
– Join the points ab, bc, ca, ag, bg and cg and complete the isometric view of the pyramid in box method.
(Fig 7c)

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CITS : Engineering Drawing (Mechanical) - Exercise 5