There are a great number of articles whose shapes are built up by portions of a cone surface and that of some other solid or plane figure. One such is sketched in Fig. 91. This is a semicircular-ended conical vessel with a flat back, made to fit against a wall as shown. The pattern for it is set out as explained by Fig. 92. The half-elevation A B C D is first drawn to the required dimensions; this figure also giving the shape of half the flat back. The cone part of the vessel is developed in the ordinary way, using O as the centre. The remaining half of the back can be added on to the other end of the pattern in a variety of ways. This is as good as any: - With centre O and radius O A draw the dotted curve A a, and with centre b and radius equal to
A B draw a small arc cutting the dotted curve in a; join this point to O. With centre O and radius O D draw the inner dotted curve and thus determine d as shown.
Join d to c and a to b, and thus the net pattern is completed. Add laps as required for grooving, knocking-up, and wiring; notch as in figure, and the working pattern is complete.