- Shopping Bag ( 0 items )
* The definitive guide to draughting to the latest ISO and ASME standards * An essential reference for engineers, and students, involved in design engineering and product design * Written by two ISO committee members and practising engineers.
Every article used in our day-to-day lives will probably have been produced as a result of solutions to a sequence of operations and considerations, namely:
2. Design and analysis
5. In-service (maintenance)
The initial stage will commence when an original marketable idea is seen to have a possible course of development. The concept will probably be viewed from an artistic and a technological perspective.
The appearance and visual aspects of a product are very important in creating an acceptable good first impression.
The technologist faces the problem of producing a sound, practical, safe design, which complies with the initial specification and can be produced at an economical cost.
During every stage of development there are many progress records to be maintained and kept up to date so that reference to the complete history is available to responsible employees and regulatory bodies.
For many years various types of drawings, sketches and paintings have been used to convey ideas and information. In the last decade 3D models and rapid prototypes have also become a common way of conveying design intent. However, a good recognizable picture will often remove ambiguity when a project is being discussed and assist in overcoming a possible language barrier.
British Standards are listed in the British Standards Catalogue, and the earliest relevant Engineering Standards date back to 1903. Standards were developed to establish suitable dimensions for a range of sizes of metal bars, sheets, nuts, bolts, flanges, etc. following the Industrial Revolution and used by the Engineering Industry. The first British Standard for Engineering Drawing Office Practice published in September 1927 only contained 14 clauses, as follows:
1. Sizes of drawings and tracings, and widths of tracing cloth and paper
2. Position of drawing number, date and name
3. Indication of scale
4. Method of projection
5. Types of line and writing
6. Colour of lines
7. Dimension figures
8. Relative importance of dimensions
9. Indication of materials on drawings
10. Various degrees of finish
11. Screw threads
12. Flats and squares
14. Abbreviations for drawings.
There were also five figures illustrating:
1. Method of projection
2. Types of line
3. Views and sections
4. Screw threads
First angle projection was used for the illustrations and the publication was printed on A5 sheets of paper.
During the early days of the Industrial Revolution manufacturers simply compared and copied component dimensions to match those used on the prototype. However, with the introduction of quantity production where components were required to be made at different factory sites, measurement by more precise means was essential. Individual manufacturers developed their own standard methods. Clearly, for the benefit of industry in general a National Standard was vital. Later the more comprehensive British Standard of Limits and Fits was introduced. There are two clear aspects, which are necessary to be considered in the specification of component drawings:
1. The drawing shows the dimensions for the component in three planes. Dimensions of the manufactured component need to be verified because some variation of size in each of the three planes (length, breadth, and thickness) will be unavoidable. The designer's contribution is to provide a Characteristics Specification, which in current jargon is defined as the 'Design Intent Measurand'.
2. The metrologist produces a 'Characteristics Evaluation' which is simply the Measured Value.
The drawing office is generally regarded as the heart of any manufacturing organization. Products, components, ideas, layouts, or schemes which may be presented by a designer in the form of rough freehand sketches, may be developed stage by stage into working drawings and annotated 3D models by the draughtsman. There is generally very little constructive work which can be done by other departments within the firm without an approved drawing of some form being available. The drawing is the universal means of communication.
Drawings are made to an accepted Standard, and in the United Kingdom, it is BS 8888, containing normative and informative references to international Standards. These Standards are acknowledged and accepted throughout the world.
The contents of the drawing (and annotated 3D models) are themselves, where applicable, in agreement with separate Standards relating to materials, dimensions, processes, etc. Larger organizations employ Standards engineers who ensure that products conform to British and also international Standards where necessary. Good design is often the product of teamwork where detailed consideration is given to the aesthetic, economic, ergonomic and technical aspects of a given problem. It is therefore necessary to impose the appropriate Standards at the design stage, since all manufacturing instructions originate from this point.
A perfect drawing communicates an exact requirement, or specification, which cannot be misinterpreted and which may form part of a legal contract between supplier and user.
Engineering drawings can be produced to a good professional Standard if the following points are observed:
(a) The types of lines used must be of uniform thickness and density.
(b) Eliminate fancy printing, shading and associated artistry.
(c) Include on the drawing only the information which is required toensureaccurate clear communication.
(d) Use only standard symbols and where no other method of specification exist, appropriate abbreviations.
(e) Ensure that the drawing is correctly dimensioned (adequately but not over-dimensioned) with no unnecessary details.
Remember that care and consideration given to small details make a big contribution towards perfection, but that perfection itself is no small thing. An accurate, well-delineated engineering drawing can give the draughtsman responsible considerable pride and job satisfaction.
The field of activity of the draughtsman may involve the use, or an appreciation, of the following topics.
1. Company communications Most companies have their own systems which have been developed over a period of time for the following:
(a) internal paperwork;
(b) numbering of drawings and contracts;
(c) coding of parts and assemblies;
(d) production planning for component manufacture;
(e) quality control and inspection;
(f) updating, modification, and reissuing of drawings.
2. Company standards Many drawing offices use their own standard methods which arise from satisfactory past experience of a particular product or process. Also, particular styles may be retained for easy identification; e.g., certain prestige cars can be recognized easily since some individual details, in principle, are common to all models.
3. Standards for dimensioning Interchangeability and quality are controlled by the application of practical limits, fits and geometrical tolerances.
4. Material standards Physical and chemical properties and non-destructive testing methods must be borne in mind. Note must also be taken of preferred sizes, stock sizes, and availability of rod, bar, tube, plate, sheet, nuts, bolts, rivets, etc., and other bought-out items.
5. Draughting standards and codes of practice Drawings must conform to accepted standards, but components are sometimes required which in addition must conform to certain local requirements or specific regulations, for example relating to safety when operating in certain environments or conditions. Assemblies may be required to be flameproof, gastight, waterproof, or resistant to corrosive attack, and detailed specifications from the user may be applicable.
6. Standard parts are sometimes manufactured in quantity by a company, and are used in several different assemblies. The use of standard parts reduces an unnecessary variety of materials and basically similar components.
7. Standards for costs The draughtsman is often required to compare costs where different methods of manufacture are available. A component could possibly be made by forging, by casting, or by fabricating and welding, and a decision as to which method to use must be made. The draughtsman must obviously be well aware of the manufacturing facilities and capacity offered by his own company and of the costs involved when different techniques of production are employed, and also have an idea of the likely costs when work is sub-contracted to specialist manufacturers, since this alternative often proves an economic proposition.
8. Data sheets Tables of sizes, performance graphs, and conversion charts are of considerable assistance to the design draughtsman.
Figure 1.1 shows the main sources of work flowing into a typical industrial drawing office. The drawing office provides a service to each of these sources of supply, and the work involved can be classified as follows.
1. Engineering The engineering departments are engaged in:
(a) current production;
(d) manufacturing techniques, which may include a study of metallurgy, heat-treatment, strength of materials and manufacturing processes;
(e) advanced project planning;
(f) field testing of products.
2. Sales This department covers all aspects of marketing existing products and market research for future products. The drawing office may receive work in connection with: (a) general arrangement and outline drawings for prospective customers; (b) illustrations, charts and graphs for technical publications; (c) modifications to production units to suit customers' particular requirements; (d) application and installation diagrams; (e) feasibility investigations.
3. Service The service department provides a reliable, prompt and efficient after-sales service to the customer. The drawing office receives work associated with (a) maintenance tools and equipment; (b) service kits for overhauls; (c) modifications to production parts resulting from field experience; (d) service manuals.
4. Manufacturing units Briefly, these cover all departments involved in producing the finished end-product. The drawing office must supply charts, drawings, schedules, etc. as follows:
(a) working drawings of all the company's products;
(b) drawings of jigs and fixtures associated with manufacture;
(c) plant-layout and maintenance drawings;
(d) modification drawings required to aid production;
(e) reissued drawings for updated equipment;
(f) drawings resulting from value analysis and works' suggestions.
Excerpted from Manual of Engineering Drawing by Colin H. Simmons Neil Phelps Dennis E. Maguire Copyright © 2012 by Elsevier Ltd.. Excerpted by permission of Butterworth-Heinemann. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.