When you use a closed loop belt the zigzag on the carriage shorten the length of the belt to avoid this I've mixed the original carriage and removed the zigzag and added a belt clamp. This has been done by so many than no credit to me just a bit of tinkering. This thing was made with Tinkercad. Edit it online https://www.tinkercad.com/things/1HwEExfjDWP