Round Tapering Elbow-3 Piece

6 Round Tapering 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

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 round to round on a pitch, with a few differences

Start with a vertical line 1-2. This is an outside edge and therefore a true length in the elevation view

Point 3 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 the following points. 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

Since there is no profile height at point 2, the full height at point 3 is used.

Pick up line 2-3 from the middle gore elevation view and transfer to the top baseline, 90° to the profile at point 3

Pick up the true length of line 2-3 and swing it from point 2. Remember for a round to round, we work from center going both ways. So make sure to swing this line to the left and the right side of point 1

Now, the next step is another change from a standard round 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 1-3 from the miter line of the end gore and swing it from point 1. This will create point 3.

Take profile height at point 3 and compare it to profile height at point 4. Remember to work from the outside inwards

Transfer line 3-4 from the elevation view, 90° to the difference in profile to find the true length and swing it from point 3

Take step-off 2-4 from the end gore miter line and swing it from point 2. This will create point 4

Take profile height at point 4 and compare it to profile height at point 5. Transfer line 4-5 from the elevation view, 90° to the difference in profile to find the true length and swing it from point 4

Take step-off 3-5 from the end gore miter line and swing it from point 3. This will create point 5

Take step-off 4-6 from the end gore miter line and swing it from point 4 to create point 6

Find the true length of line 6-7 and swing it from point 6
Take step-off 5-7 from the end gore miter line and swing it from point 5 to create point 7

Continue with this process until the fitting is complete at point 14. Remember that line 12-13 will have only 1 profile height and line 13-14 is an outside edge, so it will be true length in the elevation view