DRAFTING

also spelled Draughting, also called Engineering Drawing, graphical representation of structures, machines, and their component parts that communicates the engineering intent of a technical design to the craftsman or worker who produces the product. The first recognized formal treatise on engineering drawing is La Gomtrie descriptive (1801), by Gaspard Monge; in it Monge developed the theory of projecting views of an object onto three mutually perpendicular coordinate planes (such as are formed by the front, top, and side of a cube), and then revolving the horizontal (or top) and profile (side) planes into the same planes as the vertical (front) plane. His theory is the basis for all orthographic (mutually perpendicular) projection drawing, in which any object can be viewed from any direction. Most engineering drawings are made with instruments and therefore are called mechanical drawings. Drafting instruments include pencils, T-squares and triangles, compasses, protractors, and a drawing board. In orthographic projection drawing, views of an object are placed on a drawing in sequence of adjacent sides of the object. The object is viewed with a point of sight (or vanishing point) set at infinity, making the visual rays, or lines of sight, from the eye to the object parallel. The principal views are the top (or bottom), front (or rear), and right side (or left side); auxiliary views can be taken from any direction. Views are most commonly arranged by the third-angle projection system, in which the top view is drawn in a location vertically above the front view, and the side view is placed horizontally in direct line with the front view. Orthographic projections may contain conventional graphic symbols to represent standard features of objects, such as threads or machine parts. The drawings may show sectional views of an object, made by passing a cutting plane through the object's interior; and they may indicate the object's dimensions and tolerances. In pictorial orthographic projections the object is seen approximately as it would be seen by the eye. In the axonometric type, the line of sight is inclined to the principal faces and principal axes of the object, and all dimensions in the direction of the principal axes are foreshortened. In the oblique type, the view is projected on a picture plane set at an angle other than 90 degrees with the visual rays. The picture plane usually is parallel to one principal face, and the face shows true size and shape of the object. The perspective type of pictorial projection is the most realistic of mechanical drawings. The view is projected on a picture plane, and visual rays are not parallel but recede and converge at a finite point of sight. In architectural and structural drawings a separate sheet is used for each plan view or building elevation, and the individual parts of a structure are shown in assemblage. Most architectural and structural drawings are third-angle projections. Charts and graphs are simple pictorial representations drawn to illustrate the relationship of a group of facts, statistics, or records. Categories include line graphs, polar charts, bar charts, circle charts, flow charts, and nomographs. Original engineering drawings generally are preserved intact and reproductions are made for further handling. Reproduction methods include the blueprint process, which produces a print of white lines on a dark-blue background; the diazo process, which provides prints with black, blue, or red lines on a white background; and the microfilm process, in which drawings are reproduced on film at as little as one-eighth to one-fortieth the original size. also spelled draughting, also called engineering drawing graphical representation of structures, machines, and their component parts that communicates the engineering intent of a technical design to the craftsman or worker who makes the product. At the design stage, both freehand and mechanical drawings serve the functions of inspiring and guiding the designer and of communicating among the designer, collaborators, production department, and marketing or management personnel. At this stage exact mechanical drawings can clarify, confirm, or disqualify a scheme that looked promising in a freehand sketch. Actually, both the sketch and the exact mechanical drawing are essential parts of the process of designing, and both belong to the field of drafting. After the basic design has been established, drafting skills aid in the development and transmission of the wealth of data necessary for the production and assembly of the parts. For an automobile, a skyscraper, or a spacecraft, tens of thousands of drawings may be needed to convey all of the requirements of the finished product from the designers to the fabricators. The completion of the set of drawings necessary for the manufacture of a product or the construction of a project involves three important factors: (1) itemization of every detail and requirement of the final product or project; (2) application of good judgment and knowledge of standard drafting procedures to select the combination of drawings and specifications that will convey the information identified in stage (1) in the clearest possible manner; and (3) deployment of skilled personnel and suitable equipment to produce the documents specified in stage (2). Drafting is based on the concept of orthographic projection, which in turn is the principal concern of the branch of mathematics called descriptive geometry. Although preceded by the publication of related material and followed by an extensive development, the book Gomtrie descriptive (1798) by Gaspard Monge, an 18th-century French mathematician, is regarded as the first exposition of descriptive geometry and the formalization of orthographic projection. The growth and development of the drafting profession were favoured by the application of the concepts published by Monge, the need to manufacture interchangeable parts, the introduction of the blueprinting process, and the economy offered by a set of drawings that in most cases made the building of a working model unnecessary. Persons with a variety of skills and specialties are essential to the design and implementation of engineering and architectural projects. Drafting provides communication among them and coordination of their activities. The designer has primary responsibility for the basic conception and final solution but depends upon the support of several levels of drafters who prepare graphic studies of details; determine fits, clearances, and manufacturing feasibility; and prepare the working drawings. The delineator, or technical illustrator, converts preliminary or final drawings into pictorial representations, usually perspective constructions in full colour to help others visualize the product, to inform the public, to attract investment, or to promote sales. Before undertaking their own drawings, persons entering the profession of drafting may trace drawings to revise or repair them, then advance to the preparation of detail drawings, tables of materials, schedules of subassemblies (such as doors and windows), and the dimensioning of drawings initiated by more experienced colleagues. The wide spectrum of activities demanded of a design team requires that its members combine experience and creativity with skills in visualization, analysis, and delineation and with knowledge of materials, fabrication processes, and standards. It is the responsibility of the manufacturing, fabricating, or construction workers to follow a set of drawings and specifications exactly; there should be no need for them to ask questions or make decisions regarding particulars of the design. All such particulars are the responsibility of the design team; the drawings must clearly convey all necessary information so that the functional requirements of and regulatory restrictions on the completed product or project are satisfied, the mechanical properties of the materials are appropriate, and the machining operations and assembly or erection procedures are possible. The strictly utilitarian objectives of drafting and its emphasis on clarity and accuracy clearly differentiate it from the allied art form covered in the article drawing. Cartographic drafting is treated in the articles map and surveying. Some specific applications of drafting are dealt with in the articles building construction: Modern building practices; interior design; and clothing and footwear industry. Additional reading Aspects of drafting from basic instruction to industrial practices are treated in Walter C. Brown, Drafting for Industry (1974, reprinted 1984), a comprehensive treatment including coverage of CAD; Paul Wallach, Metric Drafting (1979), with emphasis on the use of the international metric system for dimensioning and tolerancing; and Paul C. Barr et al., CAD: Principles and Applications (1985), which covers general-purpose CAD functions and applications to industrial practice and training. William T. Goodban and Jack J. Hayslett, Architectural Drawing and Planning, 3rd ed. (1979), discusses architectural sketching and drafting, including design concepts. See also George E. Rowbotham (ed.), Engineering and Industrial Graphics Handbook (1982). Raymond A. Kliphardt