This is a rail bending jig for model railway rails. for custom track work. I built it for 00/H0 and 009/H0e scale. It works well and creates very smooth curves that can be easily incrementally tuned in radius.
It uses
1x m8 threaded rod
8x M8 nuts
3x M8 bolts
3x 8mm x7mm x22mm skateboard bearings

I will update this once i have some better photos
It prints in one piece but I recommend printing it on its top with no supports and no brim. SEE image!
It may need some light prying and cutting to release the central sliding part, I used a scalpel to gently cut it free on the short ends.

UPDATE!

I have included a file for one with a 0.5mm gap between the slide and the main body. As some printers will fuse the slide down. I have also added a picture of the correct print orientation.

UPDATE 2

I have now included a separate parts print . 3 parts in three files "bending jig part 1-3" ). The recommended print orientation is also shown in the images. the base is split in half and parts may need some sanding to fit together correctly, depending on your printer. I would suggest gluing the base parts together upside down with a flat surface, ensuring that the slide is free to move. then securing with 4 self taping screws through the 4 holes. It would be worth drilling pilot holes with a 1 or 1.5mm drill bit after gluing.