Let E F H G, in Fig. 488, be the side elevation, A B C D E the end, and IKJL the plan of a dish sometimes called a cracker boat or bread tray. The sides of the dish are parts of the frustum of a right cone. To the plan have been added the circles showing the complete frustums of which the sides are a part, L and K being the centers, all of which will appear clear from an inspection of the drawing, and below is further shown a side view of this frustum. While in the plan the top and bottom of the sides have been shown parallel, in the side view the top appears curved at C, the cut producing which curve being shown by B C of the end view.
Fig. 488. - Plan and Elevations.
Fig. 489. - Pattern.
The Pattern for a Cracker Boat.
Extend the sides U W and V X of the frustum until they meet at Z, which is the apex of the completed cone. Before the pattern can be described it will be necessary to draw a half elevation of the cone U V Z, showing the end view of the tray in its relation to the same, as in Fig. 489. Draw any center line, as K' Z'. From the point L', as center, strike the arc K' T', being one-fourth of the plan of top, as shown by K Tin Fig. 488. Below the plan of top draw one-half of frustum of cone, as shown by u' V'X' w', in which draw the end elevation of boat A' B' C X' E', letting V X' be one of its sides, and extend the line b' B' through the arc K' T' at B". Divide the part of plan B" T' into any convenient number of parts, and from the points carry lines parallel to the center line or axis until they cut the top line u' V, and from there extend them in the direction of Z' until they cut the line B' C'. Place the T-square at right angles to the axis, and, bringing it against the several points in the line B' C', which represents the shape shown by E C F in elevation of side, cut the side V' X', as shown. From Z' as center, with Z' V as radius, describe the are I'J', upon which lay off a stretchout of plan. As the part of the plan B" T' corresponds to B' C, which shows one-half of one side of boat, and as this part of plan is divided into three parts, six of these parts are spaced off on the are I' J and numbered from 1 to 4, and 4 to 1, 4 being the center line. Through these points in the stretchout draw measuring lines to the center Z', as shown. With one point of the compasses set at Z', bring the pencil point up to the several points between V and C in the elevation, and describe arcs cutting measuringliins of corresponding numbers in the stretchout; then a line traced through these points of intersection will form the line I' K' J', showing the upper line of the pattern for one side of the boat.
To obtain the bottom line of the pattern, with Z' as center and radius Z' X', describe the arc M' N'. Divide the plan of bottom of boat, as M T N in Fig. 488, into any convenient number of equal parts, in this case six, three on each side of the center T, and starting from the center line 4 of pattern, space off three spaces each way on the are M' N', thus establishing the points M' and N' of pattern, corresponding to the points M and N of plan. By drawing the lines M' I' and N' J' the pattern for one side of the boat, shown by E F H G in elevation, is completed.