Page:Sheet Metal Drafting.djvu/171

Rh the opening is represented by line DE of Fig. 214, and the length by line D-E of Fig. 213. A ⅜-inch double edge is added to the long sides and a $$\scriptstyle\frac{3}{16}$$-inch single edge to the short sides of the opening. The allowance for flanging must be computed by the formula

given in Chapter VII. Outside of this allowance a ⅜-inch wire edge is provided for covering the wire.

Pattern for Hopper Cover (Fig. 221).—This pattern is a rectangle whose length equals line AM, Fig. 214, plus ¾ in. for clearing