So I got given a mini late and needed to make us some polyurethane belts (polycord) for it. Now while these are easy to join, they are less easy to join straight and strong. You get tools that do it for you but they cost an absence amount of money as all industrial-aimed tools do. I asked to see one at the belting distributors and they let me take some pictures of it next to a ruler. Some CAD and some printing later and I had about USD 60 ish saved.

https://www.thingiverse.com/thing:2781717