. Cyclopedia of architecture, carpentry, and building : a general reference work .... at Ic1 1 5 5 is the quarter pattern for the upper curve or half of theogee, to which laps must be allowed for riveting and brazing. For the pattern for the lower curve in elevation in Fig, 117draw a line from c to D; bisect it at e and from e erect a perpen-dicular intersectincr the curve at 7. From 7 draw a horizontal lineintersecting the center line aty. Now the rule to be followed inraisincj is as follows: Divide the distance from <? to 7 into asmany parts, as the half diameter F 7 is equal to inches. I
. Cyclopedia of architecture, carpentry, and building : a general reference work .... at Ic1 1 5 5 is the quarter pattern for the upper curve or half of theogee, to which laps must be allowed for riveting and brazing. For the pattern for the lower curve in elevation in Fig, 117draw a line from c to D; bisect it at e and from e erect a perpen-dicular intersectincr the curve at 7. From 7 draw a horizontal lineintersecting the center line aty. Now the rule to be followed inraisincj is as follows: Divide the distance from <? to 7 into asmany parts, as the half diameter F 7 is equal to inches. In thiscase 7y equals 2^ inches; (any fraction up to the ^ inch is not 182 SHEET METAL WORK 111 taken into consideration, but over ^ inch one is added). Thereforefor 2^ inches use 2. Then divide the distance from e to 7 intotwo parts as shown at i and through i parallel to c D draw a lineas shown intersecting; the center line at IST. Now divide the curvec to D into equal spaces as shown by the figures 5 to 9. Let offon either side of i the stretchout from 5 to 9 as shown from 5 to. Fig. 118. 9. From i drop a vertical line intersecting F II in plan at using F as center draw the arc 23 17 as shown, which rep-resents the measuring line in plan on i in the stretchout. The student may naturally ask, why is i taken as the measuringline in plan, when it is not a stationary point, for when raising iwill be bulged outward with the raising hammer until it meetsthe point 7. In bulging the metal outward, the surface at istretches as much as the difference between the diameter at i and 183 112 SHEET METAL WORK 7. In other words, if tlie measuring point were taken on 7 itwould be found that after the mould was <^raised the diameterwould be too great: But by using the rule of dividing e 7 into asmany parts as there are inches in/ 7 the diameter will be accuratewhile this rule is but approximate. In this case e 7 has only beendivided into two equal parts, leaving but one point in whi
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