176 Print Reading for Industry Copyright Goodheart-Willcox Co., Inc. however, it is recommended the dimensioning callouts use symbols for radius and diameter and stating the machining process should be avoided unless there is a pressing reason to do so. Placement of Dimensional Values There are two methods of placing dimen- sional values on a drawing, print, or sketch. These are the unidirectional and aligned dimensioning methods. In unidirectional dimensioning, dimen- sions are placed so they read from the bottom of the drawing. With aligned dimensioning, dimensions are placed so they read either from the bottom or right-hand side of the drawing with the dimension value aligned with the dimension line, Figure 9-4. Unidirectional dimensions are the most common in industrial prints. The aligned method is more common on architectural drawings, woodworking drawings, and other drawings that use fractional expressions. The drafter or designer creating the print has one global rule that supersedes all suggestions: Dimension the drawing so it is clear and not confusing to the reader. With this in mind, the following recommenda- tions are also part of the dimensioning mechanics: • It is permissible for extension lines to cross each other. • It is desirable that dimension lines do not cross each other. • Line sub-dimensions up with each other. • Avoid crossing dimension lines with leader lines. • Small dimensions create the need to break the dimension line into two pieces, Figure 9-5. • Oblique extension lines can be used in tight quarters, but in these cases, only the extension lines are slanted, and the dimension line direction is still the same, Figure 9-6. Angular dimensions are used on prints to indicate the size of angles in degrees (°) and frac- tional parts of a degree. Fractional parts of a degree are minutes (′) and seconds (″). A complete circle Goodheart-Willcox Publisher Figure 9-4. There are two methods of placing dimensions on a drawing: unidirectional and aligned. 1.31 .67 .67 1.31 .31 .51 .51 .31 Aligned Dimensions Unidirectional Dimensions Goodheart-Willcox Publisher Figure 9-5. The dimension line must be broken and separated in various ways for small dimensional values. Goodheart-Willcox Publisher Figure 9-6. In tight situations, extension lines can be drawn at an oblique (slanted) angle, but the dimension line must maintain its direction. Oblique extension lines