There are two basic reasons why an Engineer needs to be able to sketch and to understand engineering drawings. The first reason is that there is a need to record ideas, design proposals, layouts etc in such a way that all relevant features are shown. It is important that Engineers do this in order that the information can be referred to at a later date and passed on to someone else, so that they can understand the design. How many times have people wished that they had written something down, instead of trying to rely on their memory? If their memory fails and they are the only person to suffer, then tough luck, but employers do not usually see it that way. It is also possible that their brilliant idea may be lost forever. The second reason is that it is probable somewhere along the line, that they are going to have to communicate with someone else, to show them their design so that formal layouts or drawings incorporating the design can be produced. After all, if the ideas are accepted, someone will expect to manufacture something eventually. Clearly, if they cannot communicate because they are unable to produce understandable sketches and drawings, or conversely cannot understand formal drawings produced by others, then they are likely to be a very isolated Engineer with a precarious future.
A drawing is used to transfer information, therefore there has to be an agreed standard with which everyone must comply.
British Standard 308 ( Engineering Drawing Practice ) lays down the UK version of the International conventions used in
Engineering Drawing. Sufficient related views must be provided, to ensure that information can be transferred accurately.
The method used to relate views to one another on a drawing is by projecting one from another or others. There are two basic
forms of orthographic or 'right line' projection used in the UK. These are First Angle and Third Angle. Both allow auxiliary views
and sections, provided that the direction of the view is clearly defined. The position of the views in relation to one another,
depends upon the system of projection used. The system most used in the UK and the one used in Pt 1 design is Third Angle.
It is easier to understand because related views are adjacent to one another.
REMEMBER THE WHOLE POINT OF YOUR SKETCH OR DRAWING IS TO RECORD AND TRANSFER INFORMATION.
What about a written description instead of a sketch or drawing ? Have a look at a patent, it
will give you an idea of the amount of work involved in writing a description of an engineering system.
The only pictorial projection ever used to any extent in Mechanical Engineering drawing, is Isometric and it's use has declined in recent years. It does not give a realistic picture because the drawing does not take account of perspective. Oblique projection is another pictorial projection, but is even less appealing than isometric because it is an elevation with the remainder of the view projected at 45 degrees this of course looks even less realistic. The only pictorial projection which gives a true illustration is perspective. It is a lot more involved than isometric or oblique, because viewing planes and vanishing points have to be established. These influence the whole appearance of the view and need to be chosen carefully. It is not usually considered economically viable to spend time producing views which are only intended to assist in the visualization of a component. To produce a pictorial view of an assembly involves a formidable amount of work not considered necessary. It is expected that engineers can read and use orthographic drawings and sketches. Pictorial illustrations are more useful in service manuals etc. but these are usually produced by experienced technical illustrators. Three dimensional ( 3D ) computer graphics are used quite extensively now and will eventually replace pictorial views produced by hand, but once again the amount of time required to produce these graphics, does restrict their use at present. However, it is sometimes useful to be able to show non-engineers a 3D illustration of a component or assembly, but it is likely that the graphics will have been produced by a CAD trained operator who has received the information from an Engineer, in the form of orthographic drawings or sketches. It is essential that Engineers can think in three dimensions and it is vital for them to be able to communicate using orthographic projection.
Mechanical Engineering Design Topics Page
Pages created by David Price - 9/08/95
This Information is an educational resource and is not to be reproduced (other than for private study) without
written consent of the University of Southampton. copyright © Dave Whatley 1995
GlobalSpec.com is presenting this material with the consent of Dave Whatley.
Disclaimer Whilst every care has been taken to ensure the accuracy and completeness of this information, neither the author nor the University of Southampton will accept responsibility for loss, damage etc. however arising occasioned by the use of this information.
