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Manufacturers of pipe and elbows have adopted the following standards for big end cuts for stove and conductor pipe.

As explained in Fig. 77 the center line radius is the distance measured along the base line from the center of the elbow to the center point of the diameter of the big end. The arc of the center line is also shown in Fig. 77.

Problem 13 O.—What will be the center line radius for the following elbows? (a) A 14" diameter elbow? (b) A 7" diameter elbow? (c) A 9" diameter elbow?

To get the weight of an elbow multiply the length of the center line arc by the "cut" of the big end, and this quantity by the weight per square foot of the material used.

Example.—What will be the weight of a 4", four-piece, 60° elbow made from No. 24 galvanized iron? Diameter of the elbow is 4"; Center Line Radius is 8".

Since the center line radius is 8" the center line arc must be a part of the circumference of a circle whose diameter is 16". The circumference of a 16" circle=16×π or 50.625". Since the elbow has an angle of 60° the center line arc can be but or  of the whole circle. Therefore, the length of the center line arc would be of 50.625" or 8.377". The big end cut for a 4" elbow