This is a light-box for a mechanical televisor. See the NBTV forum at https://www.taswegian.com/NBTV/forum/ to delve into that hobby.
There are two parts - the box and the lid. They are side by side so they can be printed flat. The box has a curved aperture window which is exactly the right arc shape for whatever Nipkow disk dimensions you enter as the parameters. It has a bit of a tolerance too, so you can get it to display a bit more than a frame in size. Inside the box are a number of shelves; these are to hold the plastic diffuser sheets (if you want them). Each "layer" on each shelf would be glued onto the shelf so it holds firm. Finally, although the backplate is snap-fit (should be really tight), I've put a screwdriver notch in the base so that you can leverage it off. The shelf inside prevents light entering/escaping through that slot. For wire entry/exit, just drill holes where you want 'em.
I will be modifying this thing as I iron out the design bugs, but the latest version will always be here.
17/2 New version uses a new style of lid so that there's no obstruction to inserting exact-sized circuit board.