Unit 15 Geometric Dimensioning and Tolerancing 271 Copyright Goodheart-Willcox Co., Inc. concerns must be taken into account: the lower surface must be held to a flatness tolerance of .005″and still be within a size tolerance of ±.010″ with the upper surface. Circularity Circularity is a condition in which all points on a round surface intersected by a cutting plane perpen- dicular to an axis are equidistant from the axis. Circu- larity is sometimes referred to as roundness. A circularity tolerance specifies the variation allowed for each circular element of a round surface. The tol- erance zone is defined by the maximum and mini- mum radii established by two concentric circles. See Figure 15‑21. Each circular element of the surface must lie within the tolerance zone. Circularity tolerances can be applied to cylindrical, spherical, and conical surfaces. In Figure 15-22, the circularity tolerance applied to the cylinder specifies a .005″ wide tolerance zone. The actual surface of the cylinder must lie within the tolerance zone. Cylindricity Cylindricity is a condition of a cylindrical surface where all points on the surface are equidistant from a com- mon axis. A cylindricity tolerance establishes a tolerance zone defined by two concentric cylinders. All points on the surface must lie within the tolerance zone. See Figure 15‑23. A cylindricity tolerance is a control on the circularity, straightness, and taper of a cylinder. Tolerance zone Plane perpendicular to shaft Goodheart-Willcox Publisher Figure 15-21. A circularity tolerance applied to a cylindrical surface establishes a tolerance zone defined by two concen- tric circles. Drawing Interpretation .005 tolerance zone Goodheart-Willcox Publisher Figure 15-22. A circularity tolerance specification requires each circular element of the surface to lie within the tolerance zone. Drawing Interpretation .006 tolerance zone .006 tolerance zone Goodheart-Willcox Publisher Figure 15-23. A cylindricity tolerance specification requires all points along a cylindrical surface to lie within the tolerance zone.