Introduction to Engineering Graphics

Graphics is a term derived from the Greek word “Graphikos” which means the art or science of drawing of an object on a two-dimensional surface according to mathematical rules of projection. 

Engineering drawing is a two dimensional representation of three dimensional objects. In general, it provides necessary information about the shape, size, surface quality, material, manufacturing process etc. of the object. It is the graphic language from which a trained person can visualize objects. Engineering graphics is the art of manipulation of designs of a variety of components, especially those related to engineering. It primarily consists of sketching the actual component, for example, a building or machine, with its exact dimensions and using entities such as points, lines, arcs etc. The scale of dimensions is suitably adjusted so as to properly fit within the contours of the drawing sheet.

Drawing Instruments and Aids

The Instruments and other aids used in drafting work are listed below:

• Drawing board
• Set squares
• French curves
• Templates
• Mini drafter
• Instrument box
• Protractor
• Set of scales
• Drawing sheets
• Pencils 

The three most necessary techniques of drawing/projection are: 

1) Orthographic Projection 

In this method the object is placed in space in such a way that the front view of it is captured in the vertical plane, and the top view of the same, is captured in the horizontal plane. The projections of the object are perpendicular with the planar screen. 

2) Perspective Projection 

This is a simple technique of drawing an object as how one views it. The observer's eye position, height and distance from the object, all influence the outcome of the drawing. Two sub-methods are adopted for this projection technique, namely, Visual Ray Method and Vanishing Point Method. 

3) Isometric Projection

This form of projection gives the total detail of the component under consideration. The basic principle behind isometric projection is that it involves the consideration of three axes that are inclined to each other making equal angles with each other (120°). This is followed by transfer of actual dimensions to the isometric scale involving some basic trigonometric calculations. 

Engineering drawing plays a vital role both in manufacture and design, as it not only explains the string of arrangement in a machine, but also tells us about the method to be employed to manufacture the individual blocks. An engineering drawing not only helps to convey ideas and convert concepts into reality but also follows criteria and conventions to eliminate confusion to the individual who understand when it is read, and very importantly, it indicates how something is going to be manufactured.