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Figure 3-4: Straightness Callout and Interpretation
Flatness is a specification applied to flat surfaces. It defines a tolerance zone between two parallel planes. All elements of the actual surface must fall within these two parallel planes. Flatness is a tolerance of form, not position. As a result, it does not reference any datums, and the planes defining the tolerance zone do not need to be parallel to any datums. Figure 3-5 illustrates the flatness callout and its measurement.
Figure 3-5: Flatness Callout and Interpretation
Circularity is a specification applied to cylindrical, conical, or spherical surfaces. On a cylindrical feature, it defines a circular tolerance zone on a plane perpendicular to the axis of the cylinder. An infinite number of planes can be assumed. The feature surface at each planar cross section must fall within the tolerance zone. This tolerance does not define the relationship between the cross sections at different planes. Circularity is a tolerance of form, not position, and therefore does not reference any datums. Figure 3-6 illustrates circularity tolerance for a conical feature.
Figure 3-6: Circularity Callout and Interpretation
Cylindricity is a specification applied to a cylindrical feature. It defines a cylindrical tolerance zone with a straight axis around the cylinder, within which all points on the feature’s surface must lie. Cylindricity is a tolerance of form, not position. As a result, it does not reference any datums. Figure 3-7 illustrates the cylindricity callout and meaning.
Figure 3-7: Cylindricity Callout and Interpretation
Angularity is a specification applied to a flat surface, axis, or midline of a feature. It defines a tolerance zone between two parallel planes at the specified angle from a datum. The angle will be given as a basic dimension. All points on the surface must fall between the tolerance planes. Angularity is a tolerance of orientation relative to a datum. Figure 3-8 illustrates angularity tolerance.
Figure 3-8: Angularity Callout and Interpretation
Perpendicularity is a specification applied to a flat surface, axis, or midline of a feature. It defines a tolerance zone between two parallel planes perpendicular to a datum. All points on the surface must fall between the tolerance planes. Perpendicularity is a tolerance of orientation relative to a datum. Figure 3-9 illustrates perpendicularity tolerance.
Parallelism is a specification applied to a flat surface, axis, or midline of a feature. It defines a tolerance zone between two parallel planes parallel to a datum. All points on the surface must fall between the tolerance planes. Parallelism is a tolerance of orientation to a datum. Figure 3-10 shows the parallelism callout and its meaning.
Figure 3-9: Perpendicularity Callout and Interpretation
Figure 3-10: Parallelism Callout and Interpretation
Concentricity is a specification applied to cylindrical or spherical features. It defines a tolerance zone about the axis of the feature (or center point, in the case of a sphere) within which all center points of the feature must lie. Concentricity is a tolerance of location relative to a datum axis or center point. An illustration of this is shown in Figure 3-11.
Figure 3-11: Concentricity Callout and Interpretation
Circular runout is a specification applied to cylindrical features, or features with round cross section. It defines a circular tolerance zone on a plane perpendicular to the datum axis within which all elements of the feature surface intersecting that plane must lie. An infinite number of planes can be assumed. Circular runout, unlike total runout, does not relate measurements at each section to one another. The part will be rotated about the datum in order to measure runout. Circular runout is a functional tolerance that relates the circular form at each cross section to one or more (concentric) datum axes. Figure 3-12 illustrates circular runout and its measurement.
Figure 3-12: Circular Runout Callout and Interpretation
Total runout is a specification applied to cylindrical features. It defines a cylindrical tolerance zone parallel to the datum axis within which all elements of the feature surface must lie. The part will be rotated about the datum in order to measure runout. Total runout is a functional tolerance that relates the cylindrical form to one or more (concentric) datum axes. Figure 3-13 illustrates total runout and its measurement. This specification is particularly useful when dimensioning rotating shafts that carry components like bearings or gears that are sensitive to misalignment.
Figure 3-13: Total Runout Callout and Interpretation
Profile of a surface is a specification applied to surfaces. The surfaces can be of complex shape and must be fully defined using basic dimensions. Profile of a surface defines a tolerance zone centered on the nominal surface and following the surface shape. All points on the surface must fall within the two boundary planes. Unilateral tolerancing is possible, so consult the recommended resources for more information. Profile of a surface is a tolerance of form that may or may not reference datums. When datums are referenced, the profile form and relative position are both controlled. This specification is very powerful in that regard. Figure 3-14 illustrates this callout.
Figure 3-14: Profile of a Surface Callout and Interpretation
Position is a specification applied to center points, midplanes, or axes of features. It is most commonly applied to holes and hole patterns. Position specification defines a tolerance zone around the feature’s nominal center. This tolerance zone is cylindrical in the case of hole features, and rectangular in the case of flat features. The center, midplane, or axis of the feature must lie within the tolerance zone. Position tolerance can be applied to groups of identical features and, in such a case, the tolerance zone is set up for each individual feature in the pattern. Position is a tolerance of location relative to one or more datums. Basic dimensions
