ORTHOGRAPHIC PROJECTIONS

CLASS NOTES FOR ENGINEERING

These projections are on planes at right

angles to one another. HP, VP and PP are

orthographic planes. Orthographic

projections give the top, front and side

views of a solid.

INTRODUCTION

All Orthographic projections represent a three dimensional object on a 2 dimensional drawing sheet. It gives multi-views of an object at right angles to each other. Orthographic Projections are 2 dimensional views of an object. These projections are very clear and recognized methods of communication. It helps greatly in the manufacture of any object. There are numerous languages in the world. It is difficult to communicate easily with one and another. However, Orthographic Projections remove this language barrier. It makes the world come closer in the manufacturing, transportation, repair and maintenance operations. Thus, Orthographic Projection is the Universal language in the engineering profession.

 Different Orthographic Projections

When an object is projected on planes at right angles to each other, it is called orthographic projections. Projections of an object on the HP, VP and PP are called orthographic projections. These become   top view, front view and side view of an object. These are orthographic views. In this, six views (front, back, top, bottom, left side and right side) are required to know the object fully. However, in symmetrical objects, only three views are sufficient.

Methods Of Orthographic Projections

Drawing of Orthographic projections are carried out by First Angle Projection and Third Angle Projection. First angle projection is used in Europe. Third angle projection is used in USA. Bureau of Indian Standards (BIS) recommended First angle projection by code (IS:696) in 1955. It was revised to Third Angle Projection in 1960. Further in 1973, BIS left the option to the users to use either First Angle Projection or Third Angle Projection. It was further revised in 1988 to use First Angle Projection Method. In general one should know both first and third angle projection methods for drawing front, top and side views.

Conventions in Orthographic Projections

• Represent the points of the solid by capital alphabets such as A, B, C etc.

•  Front View of a point by small alphabets with dash such as a’, b’, c’ etc.

• Top view of a point  by small alphabets without dash such as a, b, c, etc.

•  Side view of point  by small alphabets with double dash such as a”, b”, c” etc.

Utility Of Orthographic Projections

These aid in visualizing more features of an assembly. It also establishes relations between the various parts of the assembly. Use Orthographic projections in making drawings of machines, machine parts, machine assemblies and buildings etc. The advantage of this method is because of the projections are at right angles, the accurate measurements are possible. All the multi-views are on the same scale. The disadvantage is that it does not give a three dimensional form of the object. Further, it requires multi-views to understand the object. It is also really difficult to understand how the different views will fit together to form the final part. Thus it is more laborious too. Still it is very common in practice.

Given 3-D object (Bearing)

Fig. Orthographic Projections (Front, Top and Side Views)

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