In this case, where the two centre lines are at right angles, the patterns come out in an easy manner. An elevation of such a cylindrical pipe and cone fitting together is shown in Fig. 219. So that the construction lines for the patterns may be obtained, the usual method of drawing an elevation of the joint line must first be gone over. Describe a semicircle on the base line and divide it into four equal parts, running lines up through each division point to the cone axis, as shown. Now, from the points where these lines intersect the axis, draw the arcs 1" d, 2" b, and 3" a, of indefinite length. Then measure the lengths of the respective lines which are drawn across the semicircle, marking their distances along the cone axis, projecting down, and so obtaining the points a b d. Thus d V will be equal in length to 1 1° on the semicircle, b 2' equal to 2 2°, and the line a 3' equal to 3 3°. By running lines back through a, b, and c parallel to the cone axis, points on the joint curve will be determined.
The pattern for the cylindrical portion will be struck out, as before explained, by measuring off the construction lines between base line and joint curve.
The hole in the head pattern can be drawn by marking C O equal to c 0" on the elevation, and then describing the three arcs to the respective radii: C d equal to c 1", C b equal to c 2", and C a equal to c 3"; the point 4 being fixed by making C 4 equal to c 4". The lengths of the arcs, d 1", b 2", and a 3", on the elevation are then carefully measured, and their lengths set respectively along d 1, b 2, and a 3 on the pattern. The points found are then joined up, and so the shape of the hole obtained.
For stock patterns, or where a number have to be marked off the one pattern, a greater degree of accuracy will be ensured by having more construction lines, such as dividing the semicircle into six or eight parts, instead of four, as in the present example.
The dotted line on the top of the pipe pattern shows the necessary allowance for a flange for riveting on to the cone.