Hi,
What do you mean by 4 to 20mm thickness, in the same model, like a 3D part?
Or just one thickness, between 4 to 20mm?
I think, and i don’t have much experience, that if you center your camera correctly and use a ring flash, you can flash out and shadows and get a nice contour, no matter what thickness the model has. A ring flash and a low distortion lens would be recommened.
Play with apeture and speed, its not about the beauty off the picture, more the functionality, crisp edges, no shadows.
That’s my food for thoughts
Interesting project,
good luck with it