In Fig. 326, A B represents a portion of the profile of the ridge bar, or of the ventilator forming the top finish of a skylight, against which the upper end of a "common" bar is required to miter; and C D represents the profile of the curb or finish against which the lower end of the bar miters. The parallel oblique lines connecting the two show the side elevation of the bar whose profile is shown at E F F1.

As the profile consists of two symmetrical halves, either half, as E F or E F1, may be chosen to work from, and as it contains no curved portions it is simply necessary to number all of its points or angles, and then to place a complete stretchout of the same upon any line drawn at right angles to the lines of the molding, as G H, and to draw the usual measuring lines, all as shown. As a properly drawn elevation shows the intersection of the points of the profile with the two miter lines A B and C D1, it is only necessary to place the T-square parallel to the stretchout lines G H, and bring it successively against the points in A B and C D1, and cut corresponding measuring lines, as shown at I J and K L. Straight lines connecting the points of intersection will complete the pattern, as shown at I J L K. The length of the pattern, which is here shown indefinite, must be determined by a detail drawing, in which the rise M B and the run M D' are correctly given.

The patterns for the "jack" bar and for the

"hip" bar will be given later among those problems in which the development of the miter line and the raking of the profile are necessary, with which they are properly classed.

Fig. 326.   The Patterns for a

Fig. 326. - The Patterns for a "Common" Skylight Bar.