2 Manual of Engineering Drawing

presented by a designer in the form of rough freehand (e) quality control and inspection,
sketches, may be developed stage by stage into working (f) updating, modification, and reissuing of
drawings by the draughtsman. There is generally very drawings.
little constructive work which can be done by other 2 Company standards Many drawing offices use
departments within the firm without an approved their own standard methods which arise from
drawing of some form being available. The drawing is satisfactory past experience of a particular product
the universal means of communication. or process. Also, particular styles may be retained
Drawings are made to an accepted standard, and in for easy identification, e.g. certain prestige cars
this country, is BS 8888, containing normative and can be recognized easily since some individual
informative references to international standards. These details, in principle, are common to all models.
standards are acknowledged and accepted throughout 3 Standards for dimensioning Interchangeability and
the world. quality are controlled by the application of practical
The contents of the drawing are themselves, where limits, fits and geometrical tolerances.
applicable, in agreement with separate standards relating 4 Material standards Physical and chemical
to materials, dimensions, processes, etc. Larger properties and non-destructive testing methods must
organizations employ standards engineers who ensure be borne in mind. Note must also be taken of
that products conform to British and also international preferred sizes, stock sizes, and availability of rod,
standards where necessary. Good design is often the bar, tube, plate, sheet, nuts, bolts, rivets, etc. and
product of teamwork where detailed consideration is other bought-out items.
given to the aesthetic, economic, ergonomic and 5 Draughting standards and codes of practice
technical aspects of a given problem. It is therefore Drawings must conform to accepted standards, but
necessary to impose the appropriate standards at the components are sometimes required which in
design stage, since all manufacturing instructions addition must conform to certain local requirements
originate from this point. or specific regulations, for example relating to safety
A perfect drawing communicates an exact when operating in certain environments or
requirement, or specification, which cannot be conditions. Assemblies may be required to be
misinterpreted and which may form part of a legal flameproof, gastight, waterproof, or resistant to
contract between supplier and user. corrosive attack, and detailed specifications from
Engineering drawings can be produced to a good the user may be applicable.
professional standard if the following points are 6 Standard parts are sometimes manufactured in
observed: quantity by a company, and are used in several
different assemblies. The use of standard parts
(a) the types of lines used must be of uniform reduces an unnecessary variety of materials and
thickness and density; basically similar components.
(b) eliminate fancy printing, shading and associated 7 Standards for costs The draughtsman is often
artistry; required to compare costs where different methods
(c) include on the drawing only the information which of manufacture are available. A component could
is required to ensure accurate clear com- possible be made by forging, by casting, or by
munication; fabricating and welding, and a decision as to which
(d) use only standard symbols and abbreviations; method to use must be made. The draughtsman
(e) ensure that the drawing is correctly dimensioned must obviously be well aware of the manufacturing
(adequately but not over-dimensioned) with no facilities and capacity offered by his own company,
unnecessary details. the costs involved when different techniques of
Remember that care and consideration given to small production are employed, and also an idea of the
details make a big contribution towards perfection, likely costs when work is sub-contracted to specialist
but that perfection itself is no small thing. An accurate, manufacturers, since this alternative often proves
well delineated engineering drawing can give the an economic proposition.
draughtsman responsible considerable pride and job 8 Data sheets Tables of sizes, performance graphs,
satisfaction. and conversion charts are of considerable assistance
The field of activity of the draughtsman may involve to the design draughtsman.
the use, or an appreciation, of the following topics.
Figure 1.1 shows the main sources of work flowing
1 Company communications Most companies have into a typical industrial drawing office. The drawing
their own systems which have been developed over office provides a service to each of these sources of
a period of time for the following: supply, and the work involved can be classified as
(a) internal paperwork, follows.
(b) numbering of drawings and contracts,
(c) coding of parts and assemblies, 1 Engineering The engineering departments are
(d) production planning for component manufac- engaged on
ture, (a) current production;