anyone know what the rail on top of the X axis is for

[myuavbug]

Here is the Poto you requested.

QIDI X Axis-Top-Sized.jpg

[Bikeracer2020]

It is the same on my X-CF-Pro, probably part of the general construction and not for any specific purpose.

I do think the ribbon cable will fail prematurely because if a print uses the whole of the bed, that drooping ribbon cable rises and rubs on the framework in the back LH corner and then squashes into the back LH corner.

It really needs some sort of support to stop it drooping.