An Introduction to Engineering Drawings

Engineering drawing, most commonly referred to as 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 machine, with its exact dimensions. The scale of dimensions is suitably adjusted so as to properly fit within the contours of the drawing sheet.

In some cases, depending in the discipline, there are areas of particular focus, such as in the case of Structural Engineering. Another consideration is in regards to the units of measure used; these could be not only Metric or Imperial, but also the way these are noted is relevant, because it will also reflect the precision of a dimension.

Engineering drawing, is the most important aspect of mechanical engineering, as it is the fundamental need to develop the design and assembly of a machine. While the interpretation of a component in terms of sketching can be done in various methods, related to Descriptive Geometry, 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, and hence, the name 'orthographic'.
2. Perspective Projection: This is a simple technique of drawing an object as how one views it. The observer's eye position, height, and the 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 (thus the name since iso- means equal) with each other (120 deg). This is followed by transfer of actual dimensions to the isometric scale involving some basic trigonometric calculations.

In regards to projections, it is worth notice that other less conventional projections do exist, such as dimetric and trimetric projections, and these are distinguished by the angles used in contrast to 30 degrees for isometric projections. However, the most common and accepted is the orthographic projection.

As a practical way to remember how it works, one may imagine looking at a cube in an empty bowl on a table; the cube would have a face parallel to the top surface of the table. If one would grab the cube in the bowl and would rock it forward, a different side of the cube would become parallel to the table top.

Hence, 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 convey ideas and convert concepts into reality, an engineering drawing follows criteria and conventions to eliminate confusion by the the standardization of nomenclature and practices, as a way to clearly relay the information to the individual who understands it when it is read, and very importantly, it indicates or hints how something is going to be manufactured.