. 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 . h of thesespaces is bisected as shown at a, a, a, a, and lines drawnfrom these points to the apex A will give the requiredmiter line for each section of the elbow. Complete the elevation, and develop the pattern forpiece No. 1. The development is not shown on the draw-ing, as the work would be simply a repetition of theoperations described in laying out the patterns for thefour-piece 90° elbow show
. 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 . h of thesespaces is bisected as shown at a, a, a, a, and lines drawnfrom these points to the apex A will give the requiredmiter line for each section of the elbow. Complete the elevation, and develop the pattern forpiece No. 1. The development is not shown on the draw-ing, as the work would be simply a repetition of theoperations described in laying out the patterns for thefour-piece 90° elbow shown in Figure 223. The end pieces, Nos. 1 and 5, may be made any lengthat the pleasure of the workman, but the length of the 280 SHEET METAL WORKERS MANUAL heel and throat of the middle sections 2, 3, and 4, shouldbe taken from the elevation. These dimensions are shownby xx and ib in section No. 3, and cannot be changedwhen once the arc DE, representing the inner curve ofthe elbow, has been described on the drawing. DUCT ELBOWS Square or rectangular piping, or duct work, has becomea very important part of the sheet metal trade, and islargely used in the installation of heating and ventilating. Figure 226.—Rectangular Duct 90° Elbow. systems. A curved elbow, of the style generally used inthis class of work, is shown in Figure 226. These elbowsare made in four pieces, consisting of the two sides, theheel, and the throat. The heel is the outer and the throatthe inner curve. When laying out the patterns for duct elbows of thiskind, the radius for describing the inner curve or throatshould be equal to the width of the duct. The pieces areusually joined together by riveting or double seaming thecorners by means of the double-seaming stakes or handdollies. This problem is presented to give practice in the con- SHEET METAL WORK AND PATTERN DRAFTING 281 **i X X 5? $ t r-i^ i 3 f3 13 ^ to |^to t Co N <* t1 PS o « 0* Ol Or ^ oT 282 SHEET METAL WORKERS MANUAL struction of a duct elbo
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