Dimensioning an Isometric Drawing

Figure 1-10.—Isometric plumbing pipe layout. A piping diagram with a 45-degree angle, as shown in view C, would be very similar to the lines for part of the block, as shown in view B. To draw a 45-degree angle in an isometric drawing, begin with a 90-degree angle. Measure an equal distance from the intersection of the two legs connecting these points; then, establish two sides of a square. By connecting these points, you have established the diagonal, which is a 45-degree angle. In view C, point A would be the intersection of the two legs of a 90-degree angle, measured an equal distance along each leg; three fourths of an inch is used here. Now, locate points B and C. Connect points B and C, and you have established the 45-degree offset. DIMENSIONING AN ISOMETRIC DRAWING An isometric drawing, or sketch, is dimensioned with extension and dimension lines nearly like a two-dimensional drawing. The extension lines extend from the drawing, so the dimension lines are parallel to the object line and of equal length to it. To dimension the isometric drawing is more difficult because there is only a single view, and less room is available than on three separate views. Figure 1-12 shows a dimensioned isometric drawing for part of a pipe hanger. In making the isometric pipe diagram, refer to the architect’s plans and “rough in” sheets for accurate information. Since pipe diagrams are measured from the center of one fitting to the center of the next fitting, it is possible to omit the extension and dimension lines by use of a notation, such as 13 inch c to c (center to center). Pipe sizes must be added to the pipe diagram. The size of pipe is shown by a number near the line indicating the pipe, as shown in figure 1-13. 1-9