1 Large Round Elbow
When elbows or other round fittings, get too large, 12 divisions is no longer appropriate for the stretch-out. More divisions are required because the spacing of 12 becomes too great. Try and choose a number of divisions which keeps the spacing around 2”, so accuracy remains. We will layout using a quarter circle since the same quarter repeats in the pattern.
- Calculate the seam height and rise radius of the elbow
- Calculate the blank size for the elbow
- Based on the stretch-out, choose a number of divisions approximately 2” apart. For our example, we will use 40
- Draw ¼ circle of the rise radius
- Divide the quarter circle into ¼ of the divisions as you have chosen. For this example we’re using 10 divisions per quarter
- If we look at the baseline as 0°, every division will increase the angle 9°
- Using trigonometry, calculate the height at each division. This will give us 10 different numbers, starting with 0 and ending with the seam height for #10
- Because we are talking about a large elbow, it will be too big to draw, so we will sketch it or cut the metal you will be using to make the elbow
- Divide the stretch-out into the desired number, for this example it’s 40
- Label each quarter of the stretch-out using your division numbers we will use 1-10. Think of the “fish” pattern of an elbow and consider it in quarters. It goes from the seam height to the top line then back to the seam, then below the seam until the bottom line, then back to the seam height. The quarter pattern repeats, but flips.
- Using the calculated division heights, transfer those heights to the corresponding stretch-out number
- Draw in the miter line to complete the pattern