Page:Sheet Metal Drafting.djvu/226

212 {|
 * Original Order.|||Revised Order.
 * N to 1||N to B and 1
 * N to 2||N to C and 2
 * N to 3||3 to M
 * M to 4||M to 4
 * M to 5||M to 5
 * 5 to K||5 to K
 * }
 * M to 4||M to 4
 * M to 5||M to 5
 * 5 to K||5 to K
 * }
 * 5 to K||5 to K
 * }
 * }

As will readily be seen the revision is based on the fact that lines N-l, N-2, and N-3 of Fig. 301 cross the miter line at points B, C, and D.

The diagram of triangles, Fig. 304, is now constructed by drawing horizontal lines equal in length to the base lines in Fig. 301. Perpendicular lines are erected at each end of these lines and also at points B, C, and D. Since both the upper and the lower planes of the fitting are parallel there will be but one altitude to the triangles. This altitude is shown in Fig. 302 and should be placed on perpendiculars 1, 2, 3, M, 4, 5, and K of Fig. 304. The hypotenuses of these triangles may now be drawn and points H, G, and F located by the intersection of perpendiculars B, C, and D with the respective hypotenuses.

The pattern, Fig. 305, is started with a horizontal line equal to line N-O of Fig. 301. With N and as centers and a radius equal to the hypotenuse of triangle N to 1, intersecting arcs are drawn above the line, thereby locating point 1. Since both sides of the fitting are equal the pattern may be developed from points N and O simultaneously. The remainder of the pattern is developed exactly as was the square to round transition of Chapter XIII.

After the entire pattern has been developed the miter cut is developed as follows: Point E is located on line MN of Fig. 305 exactly as it appears on line MN of Fig. 301. The hypotenuse of triangle A to D is placed on line A-3 of Fig. 305, thereby locating point F. Placing the hypotenuse of triangle A to C on line A-2 of Fig. 305 locates point G, and the hypotenuse of triangle A to B placed on line A-l locates point H.

The miter cut is drawn with straight lines between points E and F and curved lines connecting points F, G, and H of Fig. 305. This completes the pattern except for locks and riveting laps.