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