I am using solid works 2019 with a student license, In a university student project (FSAE).

I am drawing a tapered sheet section that needs to be flattened so we can cut it out on our router.

It is largely defined by a series of intersecting planes rather than dimensions and angles (it is being reverse engineered from a previous design and we need to have a 'perfect' fit of the new part in the old assembly).

So I have tried building this several different ways. I tried using the sheet metal base flange then adding edge flanges one after the other placed on the planes and using intersects to draw a periphery sketch, but for some reason I couldn't get all of the edge flanges to sit exactly on the plane they were located on.

In this part I have created a surface of the desired outside mould line, then added fillets before thickening the surface to make a volume.

Then I have used 'convert to sheet metal' to try and convert the model to a sheet metal part for flattening. Unfortunately I can only get the part to flatten 8 of the 9 surfaces on the circumference, and none of the radial surfaces will flatten at all. I have tried to add cutouts to remove anything that looks like it will be a complicated bend but the error messages keep coming.

Can anyone tell me what I am doing wrong?

Note on this flat pattern there should be one more panel on the edge at the "top" of the part, which should be symmetrical to the first flange at the bottom.