Fig. 5.

First construct a rectangle A D E B 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 A B, draw the line J H, and from the point F, the middle of the line A D, draw the line F G; from the point J draw two diagonal lines J D and J E: then span the dividers so as to divide one of these diagonal lines into six equal parts, viz., J, L, 0, T, 0, V, E: from the point L erect a perpendicular, produced to the line J H ; from the point of contact M, as a centre, describe the arc N J 0 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 N 0 and N 0; then draw an indefinite straight line P Q tangent to the arcs N O and N J, 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 T S, T S, T S, and T S; these arcs and the arcs N 0, N J O, and 0 N will be the right angled elbow required.