Page:Popular Science Monthly Volume 91.djvu/317

 Sheet Metal Working Simply Explained

III. — One-piece pattern for making a twenty - sided steeple ornament

By Arthur F. Payne

Assistant Professor Manual Arts, Bradley Polytechnical Institute

��THE problem for the development of a pattern for a twenty-sided finial is very interesting. Glancing at the drawing of the finial it will appear difficult to lay out a one-piece pattern of tin in such a manner that when it is bent up it will take the shape shown in the finished drawing, but if the drawing is given close attention and study it will be readily seen that all of the twenty faces are of the same size and shape, and that each face is an equilateral triangle; that is, a triangle having three sides the same length.

It is necessary to get first a true pattern of one of these faces. The No. 4 face is the only one that is lying flat on the paper, all the others are apparently re-

��To lay out a pattern for such a finial it is necessary to know first how large the finial is to be when finished. For conven- ience of this problem we will consider one 10 in. in diameter at the widest part. The steps taken in order are as follows: (1) Draw a circle 10 in. in diameter — see dotted circle in upper view. (2) Divide circle into five equal parts and connect these points with straight lines. (3) Pro- ject one of these lines down for the top line of the triangle 4 of the front view. (4) With a pair of compasses and a ruler draw the triangle 4 with all sides equal in length. This is the true pattern for one face. (5) Draw this pattern as No. 4 face in the "full pattern" and then draw

���A pattern in one piece having twenty faces, each of the same size and shape, or an equilateral triangle, to make a twenty-sided finial to be shaped from sheet metal for a steeple ornament

��ceding from the surface of the paper. When a face is lying flat on the paper, as this one mentioned, it is called "lying in the plane" of the paper. All such faces are true patterns.

��the other faces exactly as shown in the full pattern.

Cut the pattern out of tin and proceed to bend on the dotted lines. It will be necessary to bend the top and bottom row

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