A number of things need to come together to eliminate any lead screw wobble.
Start
by making sure that the gantry's linear guides are tight against the
pillar. The guides should not be over tightened though, they should
still allow for motion of the gantry. When rotating the eccentric guides
to tighten against the pillar check that you are still able to move the
gantry by rotating the lead screw.
Next is the positioning of the lead screw and motor shaft inside the coupling:
https://makertech-3d.dozuki.com/Guide/Stage+06:+Gantry/56?lang=en#s624
Make sure that inside the coupling the lead screw and motor shaft are touching - there should be absolutely no gap.
Finally
is the lead screw bracket and cap. The lead screw cap will need proper
lubrication in order to be effective, the best in our opinion is dry
bike chain lubricant (Teflon kind), but cooking oil (olive/vegetable)
works well too.
The lead screw bracket needs to be installed as flat as possible, if installed at an angle it will cause z-wobble.The bracket also needs to be pressing down on the lead screw to prevent any vertical movement.
The linear guides, the coupling and bracket all need to be setup correctly, as outlines here, for the best results.
Checking:
Manually
rotate the lead screw moving the gantry up and down, if there is any
binding/bouncing of the gantry or stretching of the coupling then the
bracket isn't pressed down on the lead screw enough or there is a gap
between the lead screw and motor shaft inside the coupling.
In pronterface move the gantry up and down whilst looking at the gantry
from the front of the printer, check to see if there's any side to side
wobbling at the front end of the gantry, nearest the LCD display. If
there is then either the lubricant is not effective enough or the
bracket has been fixed at an angle.
Also remember that the lead screw itself wobbling is OK and expected, that wobble should however not translate over to the gantry arm and hence the print.
Finally, it's think it's worth mentioning that metal couplings are also available
if anyone is still struggling with z-wobble and is wondering if any
component itself could be upgraded. If you are considering this upgrade
then we recommend the type that clamps onto the shaft, the correct size
is 5x8.
Make sure to still follow these steps, even with a metal coupling.
https://www.aliexpress.com/item/4000281764467.html?