Page:Sheet Metal Drafting.djvu/159

Rh Pattern of Sides.—The pattern of the sides, Fig. 196, is produced in like manner. Instead of the single edge, however, a double edge is added to the edges that are to double seam onto the ends.

Pattern of Neck.—A line of stretchout, Fig. 197, is drawn and upon it is laid off twice as many spaces as there are in the half-profile of Fig. 193. Perpendiculars are erected at the points 9 and 9, Fig. 197. One-fourth inch edges are added to each end for the standard tin lock, and a -inch edge for the bead and flange joint notching as shown in Fig. 197.

Pattern of Bottom.—A rectangle. Fig. 198, whose dimensions are ¾ in. less than the top dimensions of the box, is drawn. The center is located by drawing the diagonals of this rectangle. From this center, a circle whose diameter is ⅛ in. less than the diameter of the neck, is drawn as shown in Fig. 198. This circle is cut out of the metal to provide an opening for the neck, and is always made smaller because the bead "draws in" when it is turned in the thick edge. A ¼-inch double edge is allowed on all sides to provide for double seaming the bottom to the body of the box. Over-all dimensions are placed on all views.

65. Related Mathematics on Register Boxes.—Problem 34A.— Furnace pipe tin is made in the sizes listed in the following table. Which size would you use in making the register box shown by Figs. 193 to 198 inclusive, in order to maintain as little waste as possible?

Problem 34B.—Any register has a series of holes cast in its face to correspond to some predetermined design. This design necessarily shuts off part of the opening, thereby retarding the flow of air through the register. Since most makers use nearly the same design, it has become the custom to deduct 33⅓ per cent of the area