In Fig. 349, let A BCDE E1 D1 C1 B1 A1 represent the four-pieced elbow in elevation, F G H J its profile, and K L M N the elevation of the pipe which intersects the elbow through a miter joint. In line with the pipe draw the profile of same, as indicated by O P R S. Extend F H of the profile of elbow, upon which as a center line draw another profile of the small pipe, as shown by O1 P1 R1 S1. Divide both profiles of the small pipe into the same number of parts, commencing at the same points in each, as S and S1. Now parallel to F P1 of the profile draw lines from the points in O1 P1 R1 S1 intersecting the profile F G H J. as shown.
Fig. 349. - Pattern for the Fipe Intersecting an Elbow Through Out of the Miters,
A profile should properly be drawn in its correct relation to the part of which it is the section. As the part C D D1 C1 is about to be considered first, the profile should be placed with its center line F H at right angles to C D; but as in a regular elbow of any number of pieces the miter lines all bear the same angle with the sides of the adjacent pieces, the profile may for convenience be placed in proper relation to one of the end pieces, after which lines may be carried from it parallel to the side it represents to the miter line, thence from one miter line to another, always keeping parallel to the side, continuing this throughout the entire elbow if necessary. Therefore parallel to D E of the elevation draw lines from the points in G H of the profile, cutting the miter line D1 D, and continue these lines parallel to D C and C B. From the points in the profile O P R S draw lines parallel with L K intersecting lines of corresponding numbers drawn from G H. A line traced through these intersections will give the miter line K Z N. From the point Z in the miter line carry a line back to the profile of the pipe, as indicated by Z a. This gives, upon the profile of the pipe, the point at which the miter line K N crosses the miter line of the elbow C C1, so that it can be located upon the stretchout line, where it is marked a1.
For the pattern of the pipe K L M N proceed as follows: At right angles to K L draw the line M1 M2 upon which lav off the stretchout of O P1 R S, as shown by the small figures, through the points in which, and at right angles to it, draw the usual measuring lines, which intersect with lines of corresponding numbers drawn at right angles to the line of the pipe L K from the intersections on the miter line K Z N. A line traced through the intersections thus obtained, as shown by M1 N1 K1 N2 M2, will be the required pattern for the intersecting pipe.
To avoid confusion of lines in developing the patterns of the intersected pieces of the elbows a duplicate of those parts, as shown by B C D D1 C1 B1, is given in Fig. 350, in which the miter line K Z N is also shown. The profiles FGHJ and O1 P1 K1 S1 are presented merely to show the relationship of parts, as the patterns are obtained from the miter line K Z N, in connection with the stretchout of as much of the profile as is covered by the intersection. It is not necessary to include in this operation the entire elbow pattern, therefore only such a part of the pattern will be developed as is contained in profile from V to H.
For the pattern for that portion of elbow shown in elevation by U Z N or V H of profile, proceed as follows: At right angles to C D of elevation draw the line R S, upon which lay off the stretchout of V H of the profile, as indicated by the small figures, through which draw the usual measuring lines at right angles to it, which intersect with lines of corresponding numbers drawn from the intersections on the miter line Z N at right angles to C D. Trace a line through the intersections thus obtained, as shown by U2 Z3 N1. Then will U3 Z3 represent the pattern for that part of elbow shown in elevation by U Z, and Z3 N1 be the pattern for the cut on the miter line Z N. The pattern for the other half of opening shown by N1 X V2 S is simply a duplicate of the half just obtained reversed. Then X N1 Z2 shows the shape to be cut out of what would otherwise be a regular elbow pattern. The point a in the profiles O1 S1 and V II is so near the line drawn from the point 4 that separate lines are not shown, and on this account when obtaining the shape of K1 Z1 the points 4 and a are shown on the same line.
In order to show that the pattern is produced by the regular method - that is, by the intersection of points from the miter line into lines of corresponding number in the stretchout - it should be noted that the profile and stretchout of the piece already developed is properly designated by the figures 1, 2. 3, a, 5, 6, while that of the piece next to be considered is properly designated by the figures 1, 2, 3, 4a, 5, 6, the point 4 not occurring in the first piece at all, while the points 4 and a both fall upon the same line in the stretchout of the second piece, all of which is clearly shown. The pattern of the cut on the miter line K Z is obtained in the same manner as for Z N. At right angles to B C draw the line R1 S1, upon which place the stretchout of V H of the profile, as shown.
Fig. 350. - Patterns for the Pieces of an Elbow Intersected by the
Through the points in the stretchout and at right angles to same draw the usual measuring lines, which intersect with lines of corresponding numbers drawn from the intersections on the miter line K Z, at right angles to B C. Trace a line through the intersections thus obtained, as shown by K1 Z1 U1. Then will Z1 U1 represent the pattern for that part of elbow shown in elevation by Z U. and Z1 K1 be the pattern for the cut on the miter line Z K. The pattern for the other half of opening shown by K1 X1 V1 S1 can be obtained by duplication. Then will X1 K1 Z1 represent the shape to be cut out of the regular elbow pattern.