Page:Popular Science Monthly Volume 91.djvu/955

 Simple Designs for Sheet Metal Working

VII. — Development of patterns for tee-joints of various angles By Arthur F. Payne

Former Director of Vocational Education at Columbia University

��TO those who have followed this series of articles, the new elements in the development of patterns to be con- sidered now will be easily mastered. The tee-joint made of square pipe, as shown in Fig. i, was chosen to illustrate this prob- lem, because it is much easier than the tee- joint made from round pipe, although the method used is the same in both cases.

To develop the pattern for the square tee-

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��The manner of laying out the lines in making a draft for a ninety - degree square pipe

joint having an angle of 90 deg., first draw the front view A. Be very careful and do not confuse the diagonal size of the pipe with the square size. It is best to make sure of this by drawing the end view B the size wanted; then project the sizes to the front view, and draw the bottom view C. Number the corners from 1 to 5 as shown. To develop the pattern for the vertical pipe, draw the base line D-E and find the length of this base line by laying off the distances between the numbered corners on the bottom view C. Draw lines up- wards from these points on the base line. Project corner 1 and 5 on the bottom view upward until the line strikes the bottom of the horizontal pipe; then run the line over to the right until it crosses the lines 1 and 5 coming up from the base line D-E. Make a cross where the same numbered lines cross each other, and run up and over corners 3, 2 and 4 from the bottom view and over to the right until they intersect the similarly

��numbered lines coming up from the bottom view. Connect the crosses with straight lines and you have developed the pattern for the vertical pipe.

To develop the pattern for the horizontal pipe, number the corners of the pipe, as shown in the end view F; project upwards the width of the pipe and lay off the correct length on the line H-K by stepping off the distance between the numbered corners of the end view. To develop the pattern for the hole G, project point 2 of the end view over to the front view until it strikes the joint line, then go upward until it crosses the line 2 coming up from the line H-K, and make a cross where the lines come to- gether. Do the same with points 4 and 3. Connect the crosses with straight lines and you will have the pattern for the horizontal pipe.

The hole G in this pattern will have to be cut out with a chisel or a hollow punch. Some metal workers object to this and prefer to have one half of the hole on each edge where it can be easily cut out with a pair of snips. The dotted lines on the pat- tern show where the hole would be in this case. To develop the pattern with the hole on the edges, simply mark the seam at

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��A square pipe pattern of forty-five degrees is developed like one of ninety degrees

the bottom of the pipe at 3 and number it 1 instead of 3.

To develop the patterns for the square

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