Page:Popular Science Monthly Volume 92.djvu/473

 Simple Designs for Sheet Metal Working

X — Radial line development of patterns for cones and parts of cones By Arthur F. Payne

Forroer Director of Vocational Education, Columbia University

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��MOST of the patterns developed in this series up to the present time have been for objects cylindrical in shape. The majority have been elbows and tees. These cylindrical patterns all

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��Cylindrical patterns all belong to the parallel line group. All lines parallel

belong to the parallel line group, that is all the lines in the drawing are parallel lines as in Fig. 1, which was demonstrated in the June, 1917, issue.

In Fig. 2, we see the first problem of the group of patterns developed by means of radial lines. The patterns developed by this method are all of objects that are conical in form. In the illustration we have a perspective drawing of a cone, marked A, also a front view marked B, a bottom view marked C, and the pattern for the cone. The three parts of a cone, base, apex, altitude, are also indicated.

The method of developing the pattern for this simple cone is easily understood. First, draw the front view B the size desired. Second, draw the bottom view C, which is, of course a circle, the diameter of which is equal to the base of the cone. Third, divide the bottom view into six- teen equal parts. Fourth, set your pencil dividers with one point at the apex of the cone and the pencil point at the right corner of the base, then draw the arc D-K. Get the correct length by measuring one of the spaces on the bottom view and

��stepping it off sixteen times on the arc D-E. Draw the lines from both points numbered one and the pattern for the cone is complete. This pattern is merely the size and shape obtained by tracing the outline of a cone rolled once around on a sheet of paper.

Fig. 3 shows the development of the patterns for a megaphone. It will readily be seen that this megaphone is simply two cones with their tops cut off and joined together. When the top of a cone is cut off, it is called a "truncated cone." To develop the patterns for these two "trun- cated cones," which make the megaphone, first, draw the front view as shown at B. Second, draw bottom view as shown at C. Third, to get the pattern of the large "truncated cone" B, we must first locate the "apex" of the cone, in other words, we must complete the cone. This is now done by the dotted lines meeting at F. Next we proceed in the same manner as we did in Fig. 2, that is, we divide the

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���Patterns developed by radial lines are all of objects that are conical in form

bottom view into sixteen parts, place the pencil dividers at F-G^ draw the arc D-E^

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