In Fig. 317, let A C B D be the profile of the pipe in which the elbow is to be made. Draw an elevation of the elbow with the two arms at right angles to each other, one of which is projected directly from the profile, as shown by E G I H K F. Draw the diagonal line G K, which represents the joint to be made. Divide the profile into any convenient number of equal parts. Place the T-square parallel to the lines of the arm of the elbow, opposite the end of which the profile has been drawn, and, bringing the blade successively against the several points in the profile, drop corresponding points on the miter or joint line K G, as shown by the dotted lines. Opposite the end of the same arm, and at right angles to it, lay off a stretchout line, M N, divided in the usual manner, and through the divisions draw measuring lines, as shown. Place the blade of the T-square at right angles to the same arm of the elbow, or, what is the same, parallel to the stretchout line, and, bringing it successively against the points in K G, cut the corresponding measuring lines, as shown. A line traced through these points, as indicated by R P O, together with M N, will form the required pattern.
Fig. 317. - The Pattern for a Two-Piece Elbow,