In order to create the curved belts used for the TF2 sentry gun, I opted for a relatively simpler design of an actual flexible belt than making a solid 3D curve. I love geometry and math, but I'm not going to waste a week making a one use part that is completely unforgiving on mistakes. So, therefore, it's time to demonstrate how to make a flexible linked belt!
First off, I figured my overall length of belt would be roughly 28 cm. I chose a thickness of 4mm, width of 25mm, and a belt spacing of 6mm between links. The first thing I did was saw a lot of 25mm long sections of bamboo sticks, which were promptly glued together and wrapped in a layer of regular printer paper. These can be seen below, on the top right. I therefore had to make 28 links times 2 belts, times two rods per link. Lot of sawing.
The top left of the above image shows a pile of rectangular hollow boxes. These will be used to hide the flexible components of the belt. Each of these boxes are 26mm long, and about 8mm wide. I used 110lb cardstock for these, since strength is a factor for the outer sections.
The large grid sheet featured in the middle of the above image features eight rows of 6mm spaced boxes. These will be used to align all the parts together so there's less guessing and measuring involved later.
Here, you can see the progress of putting the parts together. From the bottom, going up, there's the gridded strips, the links being glued according to the boxes, then another layer of strips going on top to make a ladder.
The last thing to do is slip the 28 covers over the gaps in the belt. Before doing so, I posed the belt into a roughly final position. This involves pinching the belt supports together so they start to curve. It's harder to bend the belt into odd curves later when the belt covers are all on. After that, all that's left is to slide each part onto the belt and position them. A bit of glue is needed to hold them in place, but you also want movement too. I glued one edge of the rectangular box to the belt itself, so the other is free to move.
Here's a finished shot of the belts. There's realistically no practical reason why you would need to make these for another project, since there are few things that need covered ammo belt feeds. However, I hope that by recording my processes, you find some inspiration in solving odd problems with something interesting.