A funnel may require to be of the shape shown in
Fig. 163, which, on inspection, will be seen that its surface is composed of half an oblique cylinder for the front, two right-angled triangles for the sides, and half of a right cylinder (a round pipe whose ends are square to the centre line) for the back.
The striking out of the pattern is illustrated by Fig. 164. An elevation is drawn, and a semicircle described on the base, this being divided into six equal parts, and numbered as in the figure. Perpendiculars are run up from points
3, 4, and 5, and a line drawn through 3' parallel to 6 t. On to this line the points 6, 5', and 4' are projected by running lines square to 3' a.
The pattern is obtained by drawing in a centre line 6 6, and marking it off equal in length to 6 t from the elevation. Then the distances 6" 5", 5" 4", and 4" 3' are measured from the elevation and stepped along the centre line of pattern, as indicated. Through these points lines are drawn square to the centre line. Now set the compasses to the length of one of the small arcs, say, 3 to 4, on the semicircle, and commencing at point 6 on the pattern, mark off points 5, 4, and 3 by stepping from one line to the other, as seen. The right-angled triangle A B 3 is now marked out by making A B equal a b and 3 B equal to 3' b from the elevation. The last portion of the pattern on each end is for the straight pipe part, and this will, of course, be equal in length to the quarter-circle 3 to 0.
Allowance for wiring, grooving, or other form of jointing can be added to the pattern as required.
The typical examples shown in this and the last chapter will, it is hoped, illustrate what has been said about articles whose surfaces are compounded of the surfaces of two or more solids. In Chapter XXV (Ventilator And Chimney-Pot Bases, Hoppers, Etc). such objects as tall-boy chimney-pots and ventilator bases are dealt with.