. Sheet metal workers' manual; a complete, practical instruction book on the sheet metal industry, machinery and tools, and related subjects, including the oxy-acetylen welding and cutting process . Wired EdgeBo/f Figure 200.—Half Elevation and Details of Round Ventilator Head. m, and add laps for seaming, which will complete the one-half pattern for the cover. Round Ventilator Head.—A ventilator head which isused for a variety of purposes, and with equal efficiencyas the top for a smoke jack or a ventilator cap, is shownin Figure 200. The proportions are varied somewhat by 246 SHEET METAL WOR
. Sheet metal workers' manual; a complete, practical instruction book on the sheet metal industry, machinery and tools, and related subjects, including the oxy-acetylen welding and cutting process . Wired EdgeBo/f Figure 200.—Half Elevation and Details of Round Ventilator Head. m, and add laps for seaming, which will complete the one-half pattern for the cover. Round Ventilator Head.—A ventilator head which isused for a variety of purposes, and with equal efficiencyas the top for a smoke jack or a ventilator cap, is shownin Figure 200. The proportions are varied somewhat by 246 SHEET METAL WORKERS MANUAL different workmen. The rule usually employed is tomake the upper hood A and the lower flange C twice thediameter of the pipe D. The supports E and F are gen-erally made from band iron, riveted to the hood and pipeas shown in the drawing. The straight flange B is merelya band of metal, having the lower edge wired and theupper edge attached to the top in a similar manner as therim of the pitched cover described in this chapter. The drawing, Figure 200, is made to a scale of 3 inchesto the foot, and represents a ventilator having a 6-inch. Figure 201.—Oblong Flaring Pan with Semicircular Ends. opening. The half-section shows the construction andmethod of assembling the different parts. To construct the ventilator, first draw the elevation fullsize, making it four times larger than the scaled lower flange B has an inclination of 45° and thepitch of the upper hood A is at an angle of 30°. Sincethe upper hood is simply a flat cone, and the lower flangethe frustum of a cone, the development of their patternsneeds no explanation, as the method has been fully de-scribed in Chapter X. Flaring Oblong Articles with Semicircular Ends.—Figure 201 shows a finished view of a flaring oblong panwith semicircular ends. The body is made in two pieces,having a wire inclosed in the top edge and the bottomdouble seamed in the usual manner. Articles of thisform are ma
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