5 Square to Round Elbow-3 Piece
- From the given shop drawing, draw the elevation view of the 2 end gores, based off a given throat radius. Use the standard elbow rule for the miter angle. The 2 end gores for any tapering elbow are always drawn using parallel line.
- Connect the end goes to create the middle gore. Notice that all the size change occurs through the heel section.
- Draw profiles on both end gores, complete with element lines and labeling
- Continue the element line through the middle gore
- Create patterns for both end gores using standard parallel line development. We will use the end gore patterns to help develop the middle gore, so they must be done first
- We will now deal with the middle gore, it is developed just as a square to round on a pitch, with a few differences
- Start with baseline A-B
- Point 4 will be developed the same as usual, except we don’t have a profile attached to the middle gore. If we did, it would be called a sector not a profile, because it is inside the fitting. So we use the end profiles, which is the first difference in developing this fitting
- Using the profiles from the end gores, use difference in profile to create point 4. We can use the outside profiles because the depth of the fitting has not changed. Because parallel line was used, the depth stays consistent throughout the end gores
- Take the profile height at point 4 and place it in the square end profile along line D-A, starting at point D, moving towards point A.
- Pick up line A-4 from the middle gore elevation view and transfer to the lower baseline, 90° to the difference in profile
- Pick up the true length of line A-4 and swing it from point A
- Take the profile height at point 4 and place it in the square end profile along line C-B, starting at point C and moving towards point B.
- Pick up line B-4 from the middle gore elevation view and transfer to the lower baseline, 90° to the difference in profile
- Pick up the true length of line B-4 and swing it from point B. This has now created point 4.
- Continue with this process to find the true lengths, taking the round profile heights down to the square end to find the difference in profile, compared 90° to the length from the elevation view
- We will work 1 side of the fitting next and create point 5 next
- Find the true length of line A-5 and swing it from point A
- Now, the next step is another change from a standard square to round on a pitch. We said that the end gores must be developed first and this is where we use them. If we consider that the depth of the end gores has not changed, but for the middle gore, the length of the stretch out has changed, due to the pitch. If we look at each end gore, regardless of shape, it is longer along the miter line than the calculated stretch out. It has grown in length along the miter line, when compared to the straight stretch out. And the middle gore must attach at this point, at the miter line. So the stretch out for the middle gore must be the same length as the miter line of the end gore. So we need to use the step-off from the miter line, not the profile. The step off from the profile would leave us well short of matching the end gore to the middle gore
- Take the step-off 4-5 from the miter line of the end gore and swing it from point 4. This will create point 5.
- Find the true length of line A-5 and swing it from point A
- Take step-off 5-6 from the end gore miter line and swing it from point 5
- Find the true length of line A-7 and swing it from point A
- Take step-off 6-7 from the end gore miter line and swing it from point 2
- Pick up the true length of line 7-D and swing it from point 7. Remember this line is a true length in the elevation view
- Take the true length of A-D and swing it from point A
- Confirm the pattern is correct and make sure the wings are 90°
- Repeat going through the other side of the fitting until the full, half pattern is complete