I think it might be helpful to have a video that demonstrates for each 500 and 1000mm X-Carves:
a) X- and Y-Axis movement with motors turned off
b) belt tightness (maybe by lifting the belt in the middle of the rail)
That would help to troubleshoot because users can compare if their X-Carve is gliding the correct way (and making the right sound) when manually moving it on X and Y axis.
Same for the belt tightness.
Just an idea, maybe somebody with a well working machine can make a quick video