A circular pan or vessel, such as that shown in Fig. 236, can be raised or drawn out of the solid plate when such malleable metals as copper, brass, etc., are used. Articles of this description, when required in quantities, are drawn up out of blank discs, in two or three operations, by the aid of suitable dies in a hand or power press. When a few articles only are wanted, they are formed by hand, the disc being gradually worked over a bench-stake, by the use of mallet and hammer, until the required shape is obtained. Whether shaped by hand or machine, nearly all metals require annealing between each or every other operation.
In calculating the size of disc the thing to be kept in mind is to have a circular blank of the same area as the combined area of the bottom and sides of the vessel. This can be calculated or found by graphic construction. We will show both methods. For calculating the radius of the disc, the following rule can be used: "Add the square of the
Fig 236 radius of the pan bottom to twice the product of the radius and the depth, and extract the square root of the whole." Thus, in Fig. 237, suppose the diameter of the vessel is 2 ft., and its depth 1 ft. 6 in.; then the radius of the flat disc will be-
A much simpler method, for those not good at calculations, is shown by the construction in Fig. 237. A B is the diameter of the circular pan, C the centre of the bottom, and B D the depth. Make B E equal to B D by turning the latter line down, as shown. Now describe a semicircle on A E, centre O, and produce B D to meet the semicircle in F. Join C to F, and the line C F will give the length of the radius for the blank disc. This latter method, it should be noted, will give the same result as obtained by calculation, the construction simply being a graphical method for working out the arithmetical problem as above.
In raising up the vessel care must be taken to keep the metal at as uniform a thickness as possible. If any trimming is required to be done, or wiring put on, then a
Fig. 237 small allowance should be added to the circular plate, as shown by the outside dotted circle.