Machine DrawingsIntroductionIn learning to draw and read machine drawings, you must first becomefamiliar with common terms, symbols, and conventions. The followingparagraphs cover common terms most used in all aspects of machinedrawings.StandardsAmerican industry and the Department of Defense (DoD) follow the standardGeometrical Dimensioning and Tolerancing, ANSI Yl4.5M-1982. This isthe standard used in all blueprint production whether the master drawings aredrawn by human hand or by computer-aided drawing (CAD) equipment. Itstandardizes the production of prints from the simplest hand-made job on siteto single or multiple-run items produced in a machine shop with computer-aided manufacturing (CAM).Refer to ANSI Y14.5M-1982 when creatingor altering machine drawings. Also refer to MIL-STD-9A for Screw ThreadConventions and Methods of Specifying, ANSI 46.1 for Surface Textures, andMIL-STD-12C for Abbreviations for Use On Drawings and In Technical-Type Publications.General termsTolerances, fillets and rounds, slots and slides, keys, keyseats, and keyways,screw threads, gears, helical springs, and finish marks present commonproblems to the draftsman. Standards offer uniform solutions to theseproblems.TOLERANCES: Tolerancing is a method of indicating acceptable variationsin size or surface and appears as a minus or plus a certain amount stated infractions or decimals. The minus or plus figures are the minimum and/ormaximum value prescribed for a specific dimension. The three ways ofshowing tolerances are the unilateral method used when variation in design ispermissible in one direction only, the bilateral method, which shows theacceptable minus or plus variations, and the limiting dimensioning method,which states both the allowable minimum and maximum measurements.Continued on next page4-40
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