The inner C shaped ring is like that so the outer unlit holding part of disc could be cast from a mold as one part.
If that inner ring was a full circle the unlit parts would be comprised of 4 pieces- 2 on both sides.
You should make a completely new part that contains just the inner C ring and outer ring light up part. A fit in form.
You should take the original ring and shave it down on the other side until it has thin even thickness.
Then you cut out the inner C part. Make a two part mold off of it. This way you don't have to clean out the C ring area. Cast these parts up in resin.
Vacforming the inner ring sounds cool, but there will be a seam lines where both parts are joined together.
I'd think it would be better to use a clear resin for this part.
This part would have to be rotocast to get the even uniform thickness. I would dye the resin. Orange for orange, blue for blue. Spray paint the inside of the cast with a matte white or something like that to enhance the glow effect if it has a light system inside it
I would also suggest keying this inner ring shape.
Maybe a set of 4 simple negative cylinder shapes going in.
You only need to do one side, cast up two parts in resin, join them, bondo job on the seam line, prime and sand, two part mold the final result to make the inner ring part.
You give the inside of the outer holding ring shape the positive cylinder key forms. Squeeze them onto the inner ring.
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