. Cyclopedia of architecture, carpentry, and building : a general reference work .... Fie. 131. 194 SHEET METAL WORK 123 from the various intersections, erect lines, which are intersectedby lines drawn parallel to H I from similar numbered intersec-tions on the miter line h c. Trace the curve L ]M. L M I II showsthe pattern for the two end pieces of the elbow. As the middle section A in Fig. 131 is to overlap the two endpieces, it is unnecessary to allow for any aQlditional thickness on. rirm account of this lap when suitable flanging machines are available;but since it is desirable, in some i
. Cyclopedia of architecture, carpentry, and building : a general reference work .... Fie. 131. 194 SHEET METAL WORK 123 from the various intersections, erect lines, which are intersectedby lines drawn parallel to H I from similar numbered intersec-tions on the miter line h c. Trace the curve L ]M. L M I II showsthe pattern for the two end pieces of the elbow. As the middle section A in Fig. 131 is to overlap the two endpieces, it is unnecessary to allow for any aQlditional thickness on. rirm account of this lap when suitable flanging machines are available;but since it is desirable, in some instances, to make an allowancein the pattern for riveting, the method of allowing for this lapwill be explained. In (R), Fig. 132, lay off on the line E F the distance /Ji nequal to 7 times the thickness of the metal in use, and with radiusequal to E n draw an arc intersecting the line 1° 1 extended at the slant line from 1 to 1 and extend all the vertical linesto intersect 1 1 at 2 3 4, etc. The slant line 1 1 is the cor- 195 124 SHEET METAL \YORK rect stretchout for the middle section B. At right angles to d cdraw J K equal to 1 5 1 in (R), as shown by similar figures inJ K, throucT-h which draw lines at ricrht J K, and inter-sect them by lines drawn at right angles to d e as shown. Tracethe curved lines to produce OPUS, which is the pattern for the middle section, to which flanges are al-lowed as shown by dotted lines. The perspective of an intersectionbetwe
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