Page:Sheet Metal Drafting.djvu/28

Problem 2
GALVANIZED MATCH BOX

11. The Galvanized Match Box.—In laying out the views and the pattern for the galvanized match box, special attention should be directed to the following:

1. Locating holes accurately.
2. Showing hidden hems and surfaces.
3. Showing lapped and soldered joints.

Figure 21 shows a rectangular match box having the back raised above the other upright surfaces. There are two screw holes drilled or punched in the back.

The top edges of the back, the ends, and the front side are provided with a $\scriptstyle {\frac {3}{16}}$-inch hem so that the edge will be smooth. The hems on the top of the back and on the right end can be seen in Fig. 21, but the hems on the top of the front and the left end cannot be seen from the outside because they are hidden from view. These hems are shown by dotted lines. The dotted line is always used to show the position of a line which cannot be seen. All dotted lines in this view represent lines or edges which cannot be seen.

This box has five surfaces, a back, a front, two ends, and a bottom. A full size elevation of the end surface will appear as in Fig. 22. The hem on the top edge of the end surface is shown by a dotted line and the lap by a solid line. This end elevation is also a profile view, and dimensions taken from it can be used in laying out the line of stretchout for the pattern. The end elevation is, therefore, numbered in a way similar to that in Fig. 19 of Problem 1.

The front elevation is constructed by using the extension lines from the end elevation. This front elevation shows the length of the box, together with the location of the two holes in the back.

As in Fig. 20 of Problem 1, the line of stretchout is drawn at right angles to the view from which the pattern is to be taken. The line of stretchout should be numbered to correspond to the profile numbering in the end elevation. Extension fines dropped from the front elevation determine the outside edges of the box on the pattern. The $\scriptstyle {\frac {3}{16}}$-inch hems must be added at the top and the bottom of the stretchout line. The ¼-inch laps must also be added