This section is from the book "The American House Carpenter", by R. G. Hatfield. Also available from Amazon: The American House Carpenter.

Let A (Fig. 248) be the given moulding, and A b the rake of the roof. Divide the curve of the given moulding into any number of parts, equal or unequal, as at 1, 2, and 3; from these points draw horizontal lines to a perpendicular erected from c; at any convenient place on the rake, as at B, draw a c at right angles to A b; also from b draw the horizontal line b a; place the thickness, da, of the moulding at A from b to a, and from a draw the perpendicular line a e; from the points 1, 2, 3, at A, draw lines to C parallel to A b; make a 1,a 2, and a 3, at B, and at C, equal to a 1, etc., at A; through the points, 1, 2, and 3, at B, trace the curve - this will be the proper form for the raking moulding, From 1, 2, and 3, at C, drop perpendiculars to the corresponding ordinates from 1, 2, and 3, at A; through the points of intersection, trace the curve - this will be the proper form for the return at the top.

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