(3) Dimensioning Holes. Figure 70 (on the following page) illustrates several ways to dimension holes. Holes are usually dimensioned to their diameters because most drills, punches, and boring machines are set up in terms of diameters. Arcs are usually dimensioned according to radii.
Always locate a hole by dimensioning to its center point. Make sure that the center point of the hole is clearly defined by crossing the short sections of the center lines. The long sections of the center lines may be dimensioned as if they were extension lines.
When using leader lines, always point the arrow end of the line at the center point of the hole. Always finish the non-arrow end with a short horizontal section that will guide the reader's eye into the dimension note. Always place dimension notes so that they may be read from the bottom of the drawing.
(4) Dimensioning Angles and Holes. Figure 71 (on the following page) illustrates several different ways to dimension angles. It also illustrates the angular (dimensioned with angles) and the coordinate (dimensioned using the center lines as base lines) systems of dimensioning holes on an object.
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