A vessel of uneven taper having a circular top and an oval bottom can have the pattern for its body set out in a similar manner to that of several of the objects previously dealt with. Examination of Fig. 154 will show that its surface is formed of parts of two different sized and shaped oblique cones. The points T T show the tops of the oblique cones that are used for the end parts of the article, and the point t the apex of one of the oblique cones used for obtaining the side parts of the body surface.
A quarter-plan and two half-elevations of the vessel are first set out as shown in Fig. 155, the quarter-oval being marked out as explained in Chapter XVII (Oval Articles Of Equal Taper. Construction Of Equal-Ended Oval). The points Q and P show the centres for the end and side curves of the oval, and point 3 where the two curves meet. Having constructed the quarter-oval, divide each of the two curves into, say, three equal parts. Draw the line c a parallel to Q 3, then joining 3 to a and producing to meet the centre line in B. Run along a line from B square to the centre line, and where this intersects the end line o e produced in T, will give the apex of the oblique cone which forms the end part of the article. The apex of the oblique cone, which forms the side part, can be determined by running up a perpendicular to the base line through b, and producing line 6 d to meet it in t. With b as centre and b 5, b 4, b 3, respectively, as radii, swing around on to the base line, thus obtaining points 3', 4', and 5'. In the same way, taking B as centre, swing points 3, 2, and 1 on to the centre line, giving points 3", 2', and 1'.
To mark out the pattern, set down the line 6 t equal in length to the line 6 t in the elevation. Then, using t on the pattern as centre and radii t 5', t 4', and t 3', draw arcs of circles as shown. Now set the compasses to the length of one of the three arcs on the side oval, say, 5 6, and commencing at point 6 on the pattern, step from one arc to the other, marking points 5, 4, and 3. Join the points up to t, and produce 3 t to T, making 3 T equal in length to the line 3" T in the side elevation. Then, using T as centre and radii T 2', T 1', and T 0, from the elevation, describe arcs as seen. Now fix the compasses to the length of one of the arcs on the end of quarter-oval, say, 0 1, and commencing at point 3 on the pattern, step off points 2, 1, and 0, joining these up to T.
To obtain the necessary points for the inside curve of pattern, set the distances along from t and T respectively, as measured along the corresponding lines from t and T in the elevations down to the top line of the article - that is, the lines t D, T A, and T E on the pattern will be respectively equal to lines t d, T a', and T e on the elevations, and so with the other points.
The pattern is set out for one-half of the body only, the joints coming down the middle of the ends. Imagining that the article is turned upside down, the allowances are put on for wiring around the top edge, knocking up a bottom, and for a grooved or riveted seam.