CBSE Book Class 11 Engineering Graphics Isometric Projection

ISOMETRIC PROJECTION

7.1 INTRODUCTION

Have you ever noticed that every corner of the class room, bed room, drawing room has three mutually perpendicular lines. These three lines give us the feeling of solid (3 dimensions). 

Let us take the example of small boxes e.g. Chalk box, which are kept in front of us. If we keep the box in such a manner that its two verticalfaces and one horizontal base will be visible to us in the equiangular position at one corner then it give us feeling of solid. So we can say that if a solid is placed in such a position that its three edges are equally inclined at an angle of 120°, then the solid is placed, said to, in isometric position and this view is called ISOMETRIC PROJECTION.

Let us recall that the Orthographic Projection as one of the best way, to represent the details of any object, i.e. by principal planes of projection (HP & VP) held mutually at right angles to each other. We know that a simple machine block in standard views like Front view, Top view and Side view will look like as shown in Fig. 7.2(a).

But these views can be interpreted only by experienced persons with technical knowledge. So in an easier way, any object can be represented by a single view/drawing that shows all the faces of the object, as they appear to the observer and give us feeling of 3-D view. The solid considered above will look like Fig. 7.2(b) in single plane method. Thus ISOMETRIC PROJECTION is yet another method to represent the details of any object in simplest way. Let us find out ! How?

7.2 ISOMETRIC PROJECTION

The isometric projection of an object is a typical pictorial projection, drawn, with the object, So placed with respect to the planes of projection that all the three axes of the object are equally inclined to each other. Let us consider a cube [Fig 7.3(a)], for example, and draw its orthographic projections as in Fig. 7.3(b). 

Now turn the cube so that all the faces are equally inclined i.e. 45° to V.P. and draw its views as shown in Fig. 7.4. Here are the Front View and Side View, both show two surfaces of the cube, parallel to the plane of projection. We can see the “Body Diagonal” in its Side View, which is the longest straight line that can be drawn in a cube.

Now raise the cube up, from rear base corner of the cube, upto that level, where the Body Diagonal becomes horizontal. Let us draw its views. Here again we find two surfaces of cube in its Side View, while Front View shows all the three faces with all the three principal axes eaually inclined to the plane of projection. So theFront View of Fig. 7.5 is the desired view, which is easy to understand as well as shows all the three dimensions in a single view. This Front View is popularly known as ISOMETRIC PROJECTION.  Direction of viewing for the object will be marked as shown and it has importance to verify the position of the observer with respect to V.P. and H.P.

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