Quote Originally Posted by caall99 View Post
Your X Y gantry is sagging in the middle from the weight of the extruders. Thats why it appears as though your glass is not flat
Exactly.

All printers sag in the middle if they are using 8mm smooth rods (an 8mm smooth rod held at both ends that is 350/370mm will sag on its own) over about 300mm long.

Can you believe that originally these things used 6mm? Anything less than 10mm will sag horribly and to be honest 12mm is what everything should be using or doing what a few printers are doing and going to V-Rail aluminum extrusions so they don't sag. They even go to Bowdens but I would prefer a direct drive on 20x40, or even 20x60 if dual direct drives, instead (Bowden they use on 20x20).