Although this design will work, I don't recommend using it any longer. Please use instead my redesigned version 2, which has lots of improvements.
I uploaded a completely redesigned/improved version here: https://www.thingiverse.com/thing:2887994
First working prototype of a 6x12 pinhole camera with curved film plane.
Focal length: 65mm
Pinhole size: 0.3mm
Aperture: about f/215
Frame size: about 56x116mm
Camera base / upper film guide / camera cover:
First (non-working version) had the upper film guide integrated into the cover. Film loading (getting the film into the upper and lower film rails) was nearly impossible, so I decided to separate the upper film guide from the cover.
Some films tend to unroll, so it is also a good idea to bend two sheet metal clips which press against the film roll (I used a tin can).
The film guide is a bit rough and hard to smoothen/polish, so I am using a strip of smooth sticky tape on the left and right side of the film guide (I don't care about the rails).
Camera base, upper film guide, cover and tripod plate are put together with a M5 threaded rod, hat nuts (on the cover side) and butterfly nuts (on the tripod side).
Use a red gel with about 14mm diameter for the small window on the back of the camera. Just glue it into the window and put the little shutter blade into the rails to close it.
Shutter / Pinhole assembly:
Shutter is designed to slide into the camera base with no light seals or screws required.
Pinhole itself is a little metal foil with a diameter of 14mm which is glued to the shutter base plate. Shutter is closed by a small rubber ring. Wire trigger is just pressed into the hole in the shutter base platte.
Update after first tests: There's vignetting due to the hole in the shutter base plate being a little bit too small. So either make a bevel on the inner side of the plate or just enlarge the hole by 1-2mm.
Use the bigger knob on the left side for film advancing.
You have to use some force to get the winders into the knobs.