You said make a "shrimp waist" elbow. The steel plate is rolled into a tube and cut.

Manual lofting steps: (Take the first paragraph as an example, other methods are the same)

1) Draw the side projection of the elbow according to the actual size. Include seam lines.

2) Divide each closed wireframe graph into independent graphs according to lines. (You can cut it or draw it separately.

3) Take a pattern, draw it on another piece of paper (the center line is vertical), and draw two horizontal lines that are parallel up and down along the height of the pattern, perpendicular to the center line and with length.

It's just the perimeter of the pattern diameter. (closed rectangle)

4) Divide the pattern vertically and mark it, and then draw these bisectors vertically into the unfolded rectangle just drawn. Note that the points on the unfolded pattern must correspond to the points on the projected pattern.

5) Divide the diagonal on the pattern into equal parts along the horizontal direction. And the corresponding points. The smooth connection of intersection points obtained on the expanded sample is an expanded curve. The denser the bisection, the more accurate the curve.

6) Release the biting amount and deal with the thickness of the plate.

When cutting an elbow, you must know the bending radius, thickness and section.

Need to be graphable.