Sheet Metal Working Simply Explained 



IV. — Development of patterns for 

 three-piece elbow with adaptations 



By Arthur F. Payne 



Assistant Professor Manual Arts Bradley Polytechnic Institute 



AN interesting fact about the develop- 

 ing of a pattern for an elbow is that 

 one piece can be used for any piece of 

 pipe shown in the drawing, and many more 

 combinations are possible. 



The method used in developing this 

 pattern is exactly the same as in the 

 "Trench Periscope" and two-piece elbow 

 pattern in the June, 1917, issue, also for the 

 "Scale Scoop" in the July, 1917, issue. It 

 is the method known as the "parallel 

 line," which simply means that the pat- 

 tern is developed by means of lines parallel 



the pipe. Third, step off the base line C-D 

 equal in length to sixteen of the spaces 

 marked off on the bottom view and number 

 the points as in the drawing. This will 

 give the length of the piece of tin required 

 to make the pipe. The reason for number- 

 ing two points one is that when the piece of 

 tin is rolled up these points come together 

 at the seam, making only one point. 

 Project lines upward from these points on 

 the base line as shown by the dotted lines in 

 the drawing. Fourth, from the points on 

 the bottom view B project lines upward 



The parallel line method is used for developing this pattern for an elbow, which is used throughout 

 sheet metal working for laying out many patterns of a similar nature in round work for turns 



to each other. All cylindrical pipe prob- 

 lems are developed by this method. If you 

 will compare the problems in the issues 

 mentioned you will see that this is a fact. 



The first step in developing such patterns 

 is always to draw the front view A, of the 

 elbow to exactly the dimensions you need. 

 Second, draw the bottom view B and 

 divide it into 16 equal points. Number 

 these points starting No. 1 on the seam of 



until they intersect the joint line (see 

 dotted lines in the drawing). Fifth from 

 the point where line No. 9 of the bottom 

 view intersects the joint line E-F project a 

 line at right angles until it crosses line 

 No. 9 coming up from the base line C-D, 

 make a cross where these number nine lines 

 cross, as in the drawing. Do the same for 

 line 10 and 8,11 and 7 and so on around the 

 bottom view. Sixth, you will now have a 



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