I'm trying to make a sheet metal part. It's basically a cylinder that mates up perpendicular against another cylinder, so one end of it has a cut that turns out to be sinusoidal when flattened. It starts out as a cylinder, so I sketched a circle with a tiny gap in it to make the sheet metal cylinder. I used radial lines for the gap, so both edges of the cut intersect the center.

I was then able to unfold it just like you would expect.

I sketched the profile for the sinusoidal cut, using a spline and a lot of midpoints. I was able to extrude the cut in the unfolded part, and it all looked good.

The trouble happened when I re-folded it. The cut is gone, and it looks like one edge of the part is missing.

I am confused. Any idea what I'm doing wrong? I have attached the part file.

I also tried extruding a circular cut while the part was in its cylindrical form, but for some reason, SolidWorks didn't want to do that either.

Thank you,
Jordan