The term draughtsman's licence refers to the freedom a draughtsman has in expressing the design in drawing form. This applies, irrespective of whether a drawing is drawn by hand or on a CAD system. Any component can be represented in a variety of ways in terms of the drawing convention (i.e., number of views, sections, viewing direction, etc.) and the method of imparting the manufacturing details (i.e., the dimensions, tolerances and datum surfaces). The problem is that there are as many ways of drawing a part as there are draughtsmen or indeed draughtswomen. For example, in Figure 3.3, for the detailed drawing of the hardened insert I chose to only draw the left-hand part of the front elevation. I could just as well have drawn the whole front elevation but by doing it this way, I have saved myself time and money. The choice was mine, and in this case, I decided that the short cut method would not overly confuse anyone who read the drawing.
Other examples are shown in the drawings of the movable jaw in Figure 3.2. This is a complex part with many holes and in addition it has steps and a chamfer. The added complication is that the holes are slightly offset. Thus, I chose to draw a full front elevation with a sectioned right-hand side elevation and a part-sectioned inverted plan. The inverted plan incorporates three separate 'views'. The left-hand part has two sectional planes whereas the right-hand part of the inverted plan is unsectioned. This has allowed me to incorporate a variety of information on the one inverted plan.
The golden rule is that the designer should always avoid ambiguity and include as much information as possible to ensure that the part is returned from a subcontractor without any queries. There are two dangers in the transmission of information between the designer and the manufacturer. Firstly, information may be missing or may be ambiguous such that emails or faxes need to be passed backwards and forwards to clarify the situation. This costs extra time and money! Secondly, the last thing the draughtsman wants to have is a subcontracted part not assembling with all the other parts in the assembly because the subcontractor has interpreted the drawing in a manner that the designer did not intend. The draughtsman should always take an 'upper bound' approach when deciding how far he should go with his draughtsman's licence to minimise the influence of errors and ambiguities.
References and further reading
BS 8888:2000, Technical Product Documentation - Specification for Defining,
Specifying and Graphically Representing Products, 2000. ISO 68-1:1998, General Purpose Screw Threads - Basic Profile Part 1: Metric
Definitions, Methods of Execution and Special Indications, 1985. ISO 129-1.2:2001, Technical Drawings - Indication of Dimensions and Tolerances - Part 1: General Principles, 2001.
ISO 2162-1:1993, Technical Product Documentation - Springs - Part 1: Simplified Representation, 1993.
ISO 2162-2:1993, Technical Product Documentation - Springs - Part 2: Presentation of Data for Cylindrical Helical Compression Springs, 1993.
ISO 2163-3:1993, Technical Product Documentation - Springs - Part 3: Vocabulary, 1993.
ISO 2203:1973, Technical Drawings - Conventional Representation of Gears, 1973.
ISO 3098-0:1998, Technical Drawings - Lettering - Part 0: General Requirements, 1998.
ISO 3098-2:2000, Technical Product Documentation - Lettering - Part 2: Latin Alphabet, Numerals and Marks, 2000.
ISO 3098-3:2000, Technical Product Documentation - Lettering - Part 3: Greek Alphabet, 2000.
ISO 3098-4:2000, Technical Product Documentation - Lettering - Part 4: Diacritical and Particular Marks for the Latin Alphabet, 2000.
ISO 3098-5:2000, Technical Product Documentation - Lettering - Part 5: CAD Lettering for the Latin Alphabet, Numerals and Marks, 2000.
ISO 3098-6:2000, Technical Product Documentation - Lettering - Part 6: Cyrillic Alphabet, 2000.
ISO 6410-1:1993, Technical Drawings - Screw Threads and Threaded Parts -Part 1: General Conventions, 1993.
ISO 6410-2:1993, Technical Drawings - Screw Threads and Threaded Parts -Part 1: Screw Threaded Inserts, 1993.
ISO 6410-3:1993, Technical Drawings - Screw Threads and Threaded Parts -Part 3: Simplified Representation, 1993.
ISO 6413:1988, Technical Drawings - Representation of Splines and Serrations, 1998.
ISO 6433:1981, Technical Drawings - Item References, 1981.
ISO 7573:1983, Technical Drawings - Item Lists, 1983.
ISO 8826-1:1989, Technical Drawings - Roller Bearings - Part 1: General Simplified Representation, 1989.
ISO 8826-2:1994, Technical Drawings - Roller Bearings - Part 2: Detailed Simplified Representation, 1994.
ISO 9222-1:1989, Technical Drawings - Seals for Dynamic Application - Part 1: General Simplified Representation, 1989.
ISO 9222-2:1989, Technical Drawings - Seals for Dynamic Application - Part 2: Detailed Simplified Representation, 1989.
ISO 15786:2001, Technical Drawings - Simplified Representation and Dimensioning of Holes, 2001.
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