Dimensioning Drawings

DOE-HDBK-1016/2-93 Engineering Fabrication, ENGINEERING FABRICATION, CONSTRUCTION, Construction, and Architectural Drawings AND ARCHITECTURAL DRAWINGS Rev. 0 Page 5 PR-06 Dimensioning Drawings For any engineering fabrication, construction, or architectural drawing to be of value, exact information concerning the various dimensions and their tolerances must be provided by the drawing. Drawings usually denote dimensions and tolerances per the American National Standards Institute (ANSI) standards. These standards are explained in detail in Dimensioning and Tolerancing, ANSI Y14.5M - 1982. This section will review the basic methods of denoting dimensions and tolerances on drawings per the ANSI standards. Dimensions on a drawing can be expressed in one of two ways. In the first method, the drawing is drafted to scale and any measurement is obtained by measuring the drawing and correcting for the scale. In the second method, the actual dimensions of the component are specified on the drawing. The second method is the preferred method because it reduces the chances of error and allows greater accuracy and drawing flexibility. Because even the simplest component has several dimensions that must be stated (and each dimension must have a tolerance), a drawing can quickly become cluttered with dimensions. To reduce this problem, the ANSI standards provide rules and conventions for dimensioning a drawing. The basic rules and conventions must be understood before a dimensioned drawing can be correctly read.