CAD organization and applications

Computing developments have made a rapid and  immense impact on industry and commerce and as the degree of complexity has also increased, then training facilities have expanded accordingly. As a source of

information and communication, the Technical Press and the Internet play a very important part. Journals

from professional institutions offer impartial news, advice and guidance, opinions, and new product details.

Manufacturers and the larger suppliers of CAD equipment have set up centres around the country where

exhibitions and demonstrations are organized. Higher education establishments, private organizations and

dealerships also give specialist courses for the benefit of students and users. The mainstream engineering software programs have been written and developed in the United States and the UK. To perform complex tasks, additional programming may need to be seamlessly integrated so that they work in harmony as a unit. 

There are literally hundreds of specialist applications available. Banks, Building Societies, Airlines, all have

their own systems and via the Internet, can freely communicate with each other. This fact has also given

rise to another branch of industrial development, i.e. security. Screen sizes have increased in size and the availability of the flat screen has reduced the size of workspace required by users.

The provision of multi-layers provides a very useful method of working on CAD. Imagine transparent sheets

placed on top of each other, which may be shuffled and rearranged so that you can draw on the top. Each

of the layers underneath in the pile can be turned on or off, they may be given identification colours and selected parts of drawings moved from layer to layer if required. Assume that we want to draw plans for a house. Layer 1 could be used to draw a plan view of the building plot. Layout work is often easier if graph paper is used. On layer 2 we make our own construction grid, which is transparent graph paper with squares to any convenient scale of our choice. Using this grid under layer 3 we design a suitable ground floor layout.

Copying the position of the outside walls from layer 3 and modified as required could start layer 4 showing

the first floor layout. When all of the required plans and elevations are constructed, they can be repositioned

on a drawing arrangement. If necessary, the site layout reduced to a smaller scale. When completed, the

construction grid may be deleted. Tracing facilities and the ability to print layers together or apart are a

valuable draughting asset.

The physical equipment components of a computer system are known as the hardware. The programs and

data used on the computer are defined as the software. Another advantage of CAD is its ability to store

line systems and other entities, which are frequently used on drawings. For example, software containing

symbols to British, European and other International Standards is freely available for most engineering

applications. The draughtsman can also create libraries of regularly used parts. For repetitive use on a drawing, a typical item may be retrieved and positioned in seconds, also oriented

at any angle to suit particular circumstances. As a drawing aid, every CAD program must provide

basic geometric features, permitting the operator to blend lines and arcs etc. It is necessary in engineering

drawing to be able to determine points of tangency between straight lines and curves and between curves

of different radii.

Productivity is much improved by a program enabling you to easily draw polygons, ellipses, multiple parallel

lines and multiple parallel curves. The speed of machine drawing is increased by the use of automatic fillets

and chamfers. Layout work benefits when use is made of construction grids and the computer’s ability to ‘snap’ automatically to particular geometric points and features, will speed the accurate positioning of line work. Copy, rotate and mirror facilities give assistance when drawing symmetrical parts. Automatic cross-hatching within closed boundaries is useful in the construction of sectional views and when indicating adjacent parts and different materials. Many changes of hatch patterns are supplied with CAD programs. Filling areas in various colours is a requirement in artwork.

The ability to zoom in and out is an asset when drawing to scale. It is possible to work on fine detail in an assembly and then zoom out to observe the result in context. CAD information is stored in digital form and hence, irrespective of the size of the final printed drawing; it is possible to accurately dimension components automatically.

Manual of

Engineering Drawing

Second edition

Colin H Simmons

I.Eng, FIED, Mem ASME.

Engineering Standards Consultant

Member of BS. & ISO Committees dealing with

Technical Product Documentation specifications

Formerly Standards Engineer, Lucas CAV.

Dennis E Maguire

CEng. MIMechE, Mem ASME, R.Eng.Des, MIED

Design Consultant

Formerly Senior Lecturer, Mechanical and

Production Engineering Department, Southall College

of Technology

City & Guilds International Chief Examiner in

Engineering Drawing

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