Page:Popular Science Monthly Volume 92.djvu/791

 Simple Designs for Siieet Metal Working

��XII. — Interesting pattern problems developed by means of radial lines

By Arthur F. Payne

Director of Vocational Eklucation, Johnstown, Pa.

��IN the last issue, one of the problems developed was the pattern for the hole in the shield of a hopper. The illus- tration Fig. 1 shows the method of de- veloping the shield for a "jack pipe" or bath room ventilator pipe coming through a roof, (in the illustration the roof is drawn very small). The method used is exactly the same as for the hopper, but as the hopper was developed by radial lines and this jack pipe is developed by use of parallel lines, it will make it much easier and make a good review of the method if we briefly outline the steps of the development.

First, draw the side view A, Fig. 1, obtaining the angle of the shield from the pitch of the roof as described in the last issue. Second, draw the bottom view B. Third, project the lines from the points on

��Patter r\ Kandle

��hole, also that if we can get the correct widths on these lines we shall have the pattern of the hole. To get these correct widths we must draw the front view G, which is done as follows: Fifth, draw the pipe and the bottom view being careful to note that the numbers are turned a quarter turn to the left, number one being in front instead of on the right side. Sixth, project the lines up from the bot- tom view until they cross the same numbered lines coming over from the side view. Mark these points with a cross. Connect these crosses with a curve and

�� ���Developing a pattern to make a shield for a jack pipe and also a pattern for making a liquid measure

��the bottom view circle upward until they meet the shield line C-D. Fourth, pro- ject lines out exactly at right angles to the shield line C-D. Draw the center line E-F Now it will easily be seen that these lines give us the length of the

��we will have a correct view of the front view of the joint of the pipe and the shield. The upper part of the joint is drawn in dotted lines because it is back of the pipe and cannot be seen. Seventh, with a pair of compasses measure the

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