Page:Popular Science Monthly Volume 90.djvu/951

 Simple Designs for Siieet Metal Working

I. — Trench periscope or comer lookout for boy scouts developed from a ninety - degree elbow pattern

By Arthur F. Payne

Assistant Professor Manual Arts, Columbia University

��ONE of the most important "safety first" inventions of the present great war is the trench periscope. By the aid of this very simple invention the soldier is able to look over the top of the trench and observe the movements of the enemy in comparative safety. It is also used in looking around the corner of one of the modern zig-zag trenches when a part of a trench has been captured and the enemy is still in the other part.

The periscope is a necessity to the soldier, but there are many ways in which the out-of-door boy may use it. In "I Spy," "Hide and Seek," etc., the posses-

���as shown in the diagram. The mirrors must lie squarely across the elbow, being held in place by strips of tin soldered to the pipe on the inside and then bent over the mirrors.

For the benefit of the boy who is working in a shop and wants to make periscopes for sale, or who wants to know the inside of that mysterious process called "developing patterns" the method of developing the pattern is given. The same pattern will do for all the pieces A-B-C-D. All that is necessary is to develop the pattern for piece A. Draw the elevation "A" the size and shape of the elbow desired. Draw the bottom view of the pipe as shown. Divide the bottom view into i6 equal parts and number them. Draw the base line E-F, getting its length by taking the distance between any two points on the bottom view, and stepping it off 1 6 times. Number

��A pattern layout for the construc- tion of an ordinary elbow in sheet metal. Diagram showing mirrors

�� ��sion of a periscope gives one a de- cided advantage. It is of value in Boy Scout activities; looking over a wall, from the back of a ^iJ"V building, or from behind a bush or rock, the scout can observe the territory beyond without exposing himself. To make one, take 3 pieces of tin pipe 2'in. in diameter. The largest piece should be 20 in. long. Solder the two short pieces to the ends of the long piece at right angles to it, forming an ordinary 90 deg. elbow. Before the pieces are fastened together, fit two pieces of mirror in place in each elbow

���these points from i to 16. This will give the circumference of the pipe. It may seem strange that at each end of the base line we have a line numbered i, but when the pipe is bent around into a tube these two lines come together and form one point, as is seen in the bottom view where it is marked number i-seam. From the

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