This section is from the book "The Tinman's Manual And Builder's And Mechanic's Handbook", by Isaac Ridler Butt. Also available from Amazon: The Tinman's Manual And Builder's And Mechanic's Handbook.
[Drawn for this work by L. W. Truesdell, Tinman, Owego, N. Y.]
Original. Fig. 5.
First construct a rectangle ADEB equal in width to the diameter of the elbow, and the length equal to the circumference; then from the point J, the middle of the line AB, draw the line JH, and from the point F, the middle of the line AD, draw the line FG; from the point J draw two diagonal lines JD and JE; then span the dividers so as to divide one of these diagonal lines into six equal parts, viz. .1, L, 0, T, 0, V, E; from the point L erect a perpendicular, pro-duced to the line JH; from the point of contact M, as a centre, describe the are NJO for the top of the elbow, and from the points
M' and M' as centres, with the same sweep of the dividers, describe the arcs NO and NO; then draw an indefinite straight line PQ tangent to the arcs NO and NJ, having the points of contact at S and S; on this tangent line erect a perpendicular passing through the point N produced until it intersects the line BE produced; then place one foot of the dividers on the point of intersection R and span them over the dotted line to the point T, and with the dividers thus spanned describe the arcs TS, TS, TS, and TS; these arcs and the arcs NO, NJO, and ON will be the right angled elbow required.