Ideas are best communicated through the means of picture or drawing. The technical drawing which is used to clearly represent and fully define the requirements of the engineering items is called an Engineering Drawing. It is not just a drawing of pictures, but Engineering Drawing is also a graphical language which is used for sharing and communicating information and ideas amongst engineers. All the needed information is passed very clearly from the Engineer who designs it to the worker who has to work on it through engineering drawing.
The main purpose of the Engineering drawing is to convey the information and facts. Engineering drawing like any other language has a high degree of commonality in the interpretation though it may require some training also to understand. This is also called as the technical drawing because of the process and skills required in producing these drawings.
Thus, Engineering drawings are the technical drawings that are drawn very accurately and precisely with the help of mathematical instruments to deliver and record technical information. Complete and exact description of the things going to be manufactured or build is provided through these engineering drawings. They do not just portray the objects as they appear directly to the eyes but make use of many conventions and specialized symbols to deliver technical information very clearly. In order to interpret and understand these technical drawings, one has to have knowledge of the fundamentals of the engineering/technical drawing. So, engineering drawing is the language of the engineer. As said by Glegg also, “Words are not the natural language of engineers. Drawings are their prose, mathematics their grammar and differential equations their poetry”.
Drawing Instruments
Engineering drawing makes use of a number of quality instruments called drawing instruments which are used for making a correct and neat drawing. Most commonly used drawing instruments are: drawing board, Mini drafter, Compass (Small and Big), Drawing pencils, Eraser, Divider (small and big), Drawing sheet, Sheet fasteners, Set squares, Protractor, Ruler, Sand paper pad, pins and cello tape etc.
Information conveyed by Engineering Drawing
Following critical information are conveyed by the Engineering drawings:
Dimensions: In the accepted units, objects’ size is captured which convey the dimensions clearly.
Materials: Constituents of the item are represented.
Geometry: In various views, the shape of the object is represented. How the object looks when viewed from various angles like side, top, bottom etc.
Tolerances: For each dimension, how much variation is allowed.
Finish: used to specify the surface quality of any item, may be cosmetic or functional.
Projections and Multiple Views
All the necessary features of a drawing cannot be shown in single view sometimes, so multiple views are then used. Following are various types of views that are used:
Pictorial Projection: Three-dimensional (3D) objects are drawn in these drawings where three sides of the object (length, breadth and height) can be seen simultaneously. In these drawings, the overall shape of the object is displayed with its three sides and their dimensions. There are two standards of the pictorial projection: isometric projection and diametric projection. Isometric projection is preferred in the drawings where all the three views of the object are equally important for the good and accurate presentation of the object. In this projection, the scales are equal along each axis of the object. For example, a cube a length L. Diametric projection is preferred in drawings where one view of the object is to be represented more than the other two views of the object. In this drawing, one view is the side of interest than other two views. Therefore, along the two axes dimensions are drawn to actual and true size whereas, along the third axis, the dimensions are halved.
Figure 1 Diametric Projection
Orthographic Projection: Orthographic is derived from Greek word ‘orthos’ which means perpendicular. Thus, in orthographic projection, the projectors are perpendicular to the plane of projection and parallel to each other. In this projection, either a single drawing can be shown with all the three dimensions in one view, or it can be shown in multi-views with two dimensions of the object in every view.
Figure 2 Orthographic Projection
Auxiliary Projection: the additional planes called auxiliary planes are used to obtain the projections of the objects in the required positions without necessarily rotating them. There are two types of auxiliary planes: Auxiliary vertical planes (AVP) and Auxiliary inclined planes (AIP). These are used for drawings where an object contains the inclined plane. Through, auxiliary view, this inclined plane can be projected to its true shape and size. These drawings are shown as three-dimensional objects.
Oblique Projection: It is a pictorial projection in which projectors are inclined at an angle other than the right angle to the plane of projection and parallel to each other. Projectors are oblique to the plane of projection. The image is projected by intersecting parallel rays and on the drawing surface called projection plane; two-dimensional image of the three-dimensional source object is created. Since the object is parallel to the plane of projection, it appears same in the oblique and multi-view projection.
Section Views: Section views are either orthographic or auxiliary views along the specified plane that shows the cross section of the source object. Using, normal projection or hidden lines, the internal features of the object are not shown with clarity. So, section views are used so that internal features of the object are shown clearly.
Figure 3 Orthographic and Oblique projection
Perspective Projection: It is the three-dimensional view of an object on a plane or a flat surface as it is perceived by the human eye. In this projection, the images of objects are taken in a way similar to the cameras’ photographs. The important characteristics of the perspective projection are that, as the distance from the observer increases, the objects are drawn smaller. This projection is widely used by civil engineers and architects for displaying the proposed buildings, road tracks, railway tracks, roads and interior design etc. It is also used for showing the appearance of the advertising drawings and producing sceneries as in this projection, objects are shown as they actually appear to the human eyes. For example, the figure below shows the engineering drawing for the plan of a building.
Figure 4 Plan of a Building
Evidence from real life
Following are the examples of engineering drawing from real life: In figure 4, it is displayed how the radius of an arc is dimensioned through engineering drawing. The Arcs are always dimensioned by giving the radius of the arc.
Figure 5 Dimensioning the Radius of an arc
The Figure 5 above shows that the Arc location must be defined either at the centre of the radius or by locating to tangents to the arc. The arc centre location must be shown in its true dimension even if the centre point is not shown in its true location
Another example can be the engineering drawing of how angles, chamfers and tapers are displayed in the technical drawings. Chamfers are generally placed at 45 degrees to the width of the face specified. In angles, one vertex of an angled face is dimensioned and the other vertex is determined by the intersection. The engineering drawing of angles, chamfers and tapers are displayed in figure 6 below.
Figure 6 Angels, Chamfers and Tapers
Drawing Standards and scales
For the drawing of these objects, various standards and drawing scales are used so that drawing are understandable to everyone who reads them. Drawing standards are the rules that are used to define how technical drawings are represented. These are used so as to convey the same meaning of the drawing to everyone who reads and understands them. For example, for the United States, the standard defined is ANSI (American National Standard Institute), for Japan it is JIS i.e. Japanese Industrial standard. Drawing Scale is used to define the ratio of the real linear dimension of any object to the linear dimension of the same object shown in the drawing. Drawing scales are represented as: word “SCALE” followed by indication of its ratio like:
For Full Size: SCALE 1:1
For reduction scales: SCALE 1:X
For enlargement scales SCALE X:1
Technical Lettering: The process of forming numerals, letters and other characters in the technical drawing is called technical lettering. The detailed specification of the object is provided through lettering. Styles are standardized so as to keep uniformity and legibility.
Conclusion
Thus, it can now be concluded that Engineering drawings are the technical drawings that are drawn very accurately and precisely with the help of mathematical instruments to deliver and record technical information. These drawings can provide a complete and exact description of the things going to be built or manufactured. Many conventions, standards, drawing scales, lettering and specialized symbols are used to deliver technical information very clearly. The appearance of the buildings, road tracks, railway tracks, roads, interior design, advertising drawings and producing sceneries etc. can be shown through engineering drawings. Thus, engineering drawing is the language of the engineer.
Works Cited
Agrawal, Basant. Engineering Drawing. New Delhi: MvGraw Hill Education Pvt. Ltd., 2014.
carleton.ca. Drawings in Engineering Design. 2015. <http://http-server.carleton.ca/~gkardos/88403/drawing/Drawings.html>.
Gupta, B.V.R. Engineering Drawing. New Delhi: I.K. International Publishing House, 2008.
Henzold, George. Geometrical Dimensioning and Tolerancing for Design, Manufacturing and Inspection. New York: Elsevier Ltd. , 2006.
