Ellsworth M. Longfield

“ Problems on the Rise of the Miter Line.—An elbow is always measured by the degrees of the angle formed by straight lines drawn from its extremities to the center of the elbow, Fig. 77. Since all backsets in the same elbow are equal, the value of the backset can be expressed in degrees. A five-piece elbow has 8 backsets. A five-piece 90° elbow would have each backset equal to 90°÷8 or 111⁄4°. The first piece of any elbow contains one backset, the last piece one, and every other piece contains two. ”

“ Since the pattern for all pieces can be laid out from the pattern of the first piece, it follows that all necessary information can be obtained from an elevation of the first two pieces of an elbow. A draftsman rarely draws more than two pieces of the elevation and divides the arc of the throat instead of the arc of the back. ”

“ The figures for the third column are obtained by multiplying those of the second column by 7. The figures for the fourth column are obtained by dividing those of the third column by .0156. This will give answers in 64ths of an inch since .0156 is the decimal for . ”