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Development of Blanks for Curved Mouldings

shown, fig and machine

DEVELOPMENT OF BLANKS FOR CURVED MOULDINGS Our first attention will be given to the methods of construction, it being necessary that we know the methods of construction before the blank can be laid out. For example, in Fig. 337 is a part elevation of a dormer window, with a semicircular top whose profile has an ogee, fillet, and cove. If this job were undertaken by a firm who had no circular moulding machine, as is the case in many of the smaller shops, the mould would have to be made by hand. The method of construc tion in this case would then be as shown in Fig. 338, which shows an enlarged section through a b in Fig.

337. Thus the strips a, b, and c in Fig. 338 would be cut to the required size, and would be nothing more than straight strips of metal, while d d' would be an angle, the lower side d' being notched with the shears and turned to the required circle. The face strips e, f, and h would represent arcs of circles to correspond to their various diameters obtained from the full-sized elevation. These face and sink strips would all be

soldered together, and form a succession of square angles, as shown, in which the ogee, as shown by i j, and the cove, as shown by m, would be fitted. In obtaining the patterns for the blanks hammered by hand, the averaged lines would be drawn as shown by k 1 for the ogee and n o for the cove. The method or principles of averaging these and other moulds will be explained as we proceed.

In Fig. 339 is shown the same mould

as in the previous figure, a different method of construction being employed from the one made by hand and the one hammered up by machine. In machine work this mould can be hammered in one piece, 8 feet long or of the length of the sheets in use, if such length is required, the machine taking in the full mould from A to B. The pattern for work of this kind is averaged by drawing a line as shown by CD. This method will also be ex plained more fully as we proceed.