Using two layers of baking sheet is enought to create a very nice soft lighting setup. 
This has two circles which press-fit onto each other, with the paper tightly in between. 

For a smaller lamp diffuser, you can use the test piece I made 
(It's really tight, like a drum). 
The larger ring consist of six pieces for each side 
and the pieces are assembled overlapping. 

State 

This is version 1. 
It fully usable, but the assembly process is somewhat cumbersome. 

Warnings 

The lightbulb is quite close to the baking sheet, 
so do consider the fire risk, use at your own risk and don't leave it unsupervised. 

BOM

- Baking sheets (white) 
- Light socket (eg. E27) 
- LED bulb 

- Optional: Tri-pod as a stand 

Printing 

The mount pieces and frame you only need one. 
For the other rails you need 4 and 5. 

The frame has a 10mm hole for the lamp socket, 
which can be easily modified. 

Assembly

As the current joints do nothing, 
you will need to assemble alternating sides going around the circle. 
It is a little fidgety and the result is not as perfect as pressing full circles together 
like the test pieces. 
Still, by trial and error you will get the tightness right. 
See images. 

Usage

Use two of these or one and a reflecting surface to create a soft lighting setup for photographing 
(for example taking pictures of your prints). 

The bottom of the frame has holes for camera thread mounting.