Fig. 316 - The Pattern of a Flange to Fit Around a Pipe and Against a Roof of One Inclination.
Let L M, Fig. 316, be the inclination of the roof and P R T S an elevation of the pipe passing through it. N O then represents the length of the opening which is to be cut in the flange, the width of which will be the same as the diameter of the pipe. Let A B D C be the size of the flange desired, as it would appear if viewed in plan. Immediately in line with the pipe draw the profile G H I K, putting it in the center of the plan of the flange A B D C, or otherwise, as required. Divide one-half of the profile in the usual manner, and carry lines vertically to the line L M, representing the pitch of the roof, and thence, at right angles to it, indefinitely. Carry points in the same manner from A and B. Draw C D1 parallel to L M. Make C A' equal to A C, or the width of the required flange, and draw A1 B1 parallel to C D1. Then C1 A1 B1 D1 will be the pattern of the required flange. Draw E1 F1 through it at a point corresponding to E F of the plan, crossing the lines drawn from the profile. From E1 F1 set off on each side, on each of the measuring lines crossing it, the width of opening, as measured on corresponding lines of the plan, measuring from E F in the plan to the profile. Through the points thus obtained draw a line, which will give the shape of the opening to be cut, all as shown by G1 H1 I1 K1.