Unit 15 Geometric Dimensioning and Tolerancing 277 Copyright Goodheart-Willcox Co., Inc. ■ ■ Cylindricity is a condition of a cylindrical surface where all points on the surface are from a common axis. ■equidistant ■ Angularity is a condition of a surface, center plane, or axis that is at a specified angle (other 90°) to a datum plane or datum axis. ■than ■ Perpendicularity is a condition in which a surface or axis is at a right angle (90°) to a plane or datum axis. ■datum ■ Parallelism is a condition in which a surface or axis remains the same distance at all points a datum plane or axis. ■from ■ Position tolerances define the allowable location variation of features. A position tolerance establishes a tolerance zone within which the center point, axis, or center plane of a feature of size is allowed to vary from the (exact) position. ■true ■ A profile of a line tolerance is a two- dimensional geometric tolerance used to control variation of the individual elements a surface. ■defining ■ A profile of a surface tolerance is a three- dimensional geometric tolerance used to control of all points making up an entire surface. ■variation ■ A circular runout tolerance is a type of runout tolerance that provides control of circular of a surface relative to a datum axis. ■elements ■ A total runout tolerance is a type of runout tolerance that provides composite control of all surface elements of a feature relative to a datum axis. SUMMARY ■ ■ Geometric dimensioning and tolerancing (GD&T) is a system used to specify the allowable variation on a part with respect to the actual and relationship of part features. ■function ■ Geometric tolerances are applied to control variations in form, orientation, position, and runout. ■profile, ■ Symbols used in GD&T include geometric characteristic symbols, datum feature symbols, feature control frames. ■and ■ A datum is defined as a theoretically exact point, axis, line, or plane. A datum is used as an origin from which geometric controls of are derived. ■features ■ A basic dimension is a numeric value that states the theoretically exact size, shape, or angle of a feature or datum target. ■location, ■ A datum feature is an actual feature on a part used to establish a datum. Datum features can be identified on a drawing by using a datum symbol, datum target symbol, or note. ■feature ■ A material condition modifier is a modifier applied to a tolerance specification indicating the applicable material condition. There are three material condition designations: maximum material condition (MMC), least material condition (LMC), and regardless of size (RFS). ■feature ■ Straightness is a condition in which an element of a surface or a derived median line a straight line. ■is ■ Flatness is a condition in which all elements of a or a derived median plane lie in one plane. ■surface ■ Circularity is a condition in which all points on a round surface intersected by a cutting plane perpendicular to an axis are equidistant from the axis.