Seam Symmetry

How closed curve seam location affects rebuild.

By Darla Alvarez, GIA Jewelry Design and Technology Instructor

(Originally Published by MJSA October, 2025)

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A good strategy for creating the best possible surfaces is to rebuild your creation curves. However, the Rebuild command can distort curves in unintended ways, especially closed curves where the seam location directly impacts how the curve is restructured.

1. We’ll begin with a closed curve of an unusual shape, intended to be used as the sweep shape in a Sweep 1 command. The original curve was created from circles, ellipses, and fillets, leaving a messy, 28-point, degree 2 curve that may produce kinks when swept.

2. First, check the current location of the closed curve seam. In this case, it is in the upper right and not positioned along an axis of symmetry for the shape.

3. Next, we will rebuild the curve with the same point count but increase the degree to 3 so that Sweep 1 produces a single surface. However, the pink preview curve shows that the curve is distorting unevenly from the original shape.

4. When we turn on the control points and use white lines for symmetry reference, it is clear that the rebuilt curve is uneven. The control points do not align symmetrically across the shape.

5. Undo the rebuild and reposition the closed curve seam at the bottom of the shape, aligning it with the Y axis to divide the curve symmetrically.

6. Rebuild the curve again with the same point and degree settings. The preview now shows a smoother result: While some deviation from the original is still expected, the curve is now rebuilt symmetrically along the Y axis.

7. Turning on control points for the newly rebuilt curve and using white lines as a reference, we see that the control points are symmetrical. The closed curve seam influences how control points are distributed by the Rebuild command. To maintain a symmetrical curve when rebuilding, always move the seam to a location that promotes curve symmetry before executing the rebuild.