I got a FF creator pro last November. It's generally pretty easy to use with PLA, and I can do ABS with some extra attention. I've recently tried to use PETG, though, and was pulling my hair out trying to get the bed level due to adhesion issues. I hadn't leveled off the center of the bed before (because the bed is very flat), but when I did, I was surprised to see that the center was "high" by over twice the thickness of the provided leveling card. So I stuck a magnetic-base dial indicator to the floor of the print area (not the bed) and watched the droop of the X and Y axis rails as the carriage moved toward the center. It turns out that the carriage is drooping about 0.004" in the shorter Y axis and 0.007" in the longer X axis, for a total of about 0.28mm. No wonder I'm having miserable luck with larger prints or extrusion-sensitive material like PETG.

Does anybody have any advice on how to either reduce the droop or compensate for it? Are the 8mm x/y axis rails solid or hollow? Is there a 10mm upgrade possible?

Thanks!