Quality suffers at certain height

Hi guys, I've just finished building my corexy and I have started to print a new model and this has happened (please see attached)



Can anyone help me with this?

The bottom is flared by design, or is the bed too hot?
It the bed cantilevered? Does it bounce when the machine is running?

The decreasing quality as you go up is probably related to the machine shaking and/or the bed bouncing. Most of the movement is taking place at the top of the machine. When the bed is up there it is more closely coupled to the top of the machine and shakes along with it. As the print gets taller, the bed moves downward and is no longer tightly coupled with the shaking at the top of the frame. The result is decreasing print quality as the print gets taller. There are a couple ways to fix it. Print slower and with lower acceleration, and/or reinforce the frame so the machine doesn't shake so much.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

The frame is solid, as is the bed but I was printing about 60mm/s.
I'll try again printing slower and see what happens.
Thanks