My new 6040 improvement plan.

[magicniner]

The main gain was in Y-axis bearings.

They are adjusters. When they are tight, there is no noticeable flex/movement on the gantry. I tighten til they stop, then quarter turn to nip up. Gantry feels rock hard.

Have you tried marking the rod with a marker pen to see if the contact is simply the screw against the rod? ;-)