In the previous chapter we dealt with the marking out of patterns for sheet metal moulding or gutters that form a plain mitred joint, and in this chapter we purpose explaining the way in which cornices, guttering, etc., may be jointed, and the patterns laid out when they meet at a double rake.
In Fig. 185 a sketch is shown of a cornice running along the eaves and up the gable of a building. By jointing the corner at right angles in the ordinary way, and then forming another joint to turn the cornice up the edge of the gable, the problem in this case becomes a comparatively easy one.
An elevation of the moulding is shown in Fig. 186, the roof being pitched at an angle of 30°. The section is divided up and numbered, the sum of the lengths 0 1, 1 2, etc., up to 9 giving the girth of the moulding.
Two pattern cuts will be required, one for the part of the cornice that is horizontal, and the other for the joint formed by the small horizontal piece at turn of corner and the part of cornice running up the gable edge. The girth of the section is first laid out for the widths of the patterns, and the cross lines drawn as seen in the figure. The cut for the corner mitre will be set out in the ordinary way by making the cross lines equal in length to the correspondingly numbered lines on the moulding section. Thus, 1 1' = 0 1,
2 2' = a 2, 3 3' = a 3, and so on for the remaining lines.
The cut for the gable cornice joint will be laid out by making 2 2" and
3 3" on the pattern each equal to a a' on the elevation, 4 4" equal to b b', and so on for the remaining lengths. The cut on the pattern for the sloping piece of cornice will, of course, be the same as that on the left side of the corner-piece pattern, only reversed.
Strong joints can be made by carefully soldering on the inside of cornice, and, if required particularly strong, laps can be left on the straight parts of the edge of one pattern
(shown by the dotted lines), and these turned on to the insides of the moulding and soldered or riveted as desired.