Possibly the simplest Dual Z Axis for ender 5 (NO MORE LOOSE BED)

YOU NEED A BOARD THAT SUPPORTS 2 STEPPER MOTTORS ON ONE DRIVER 
(LIKE BTT SKR MINI E3 V3)

What you can expect after the upgrade:

The structure supports the bed on the other end, so it cant flex up and down freely like it does in the original printer. The change is the most visible when printing with higher accels (like 5k+) when the bed jolts up and down on the far end.

What you need for the build:

• 2X 8mm linear rods (at least 43cm length)
• 4X linear rod clamps (SK08)
• 1X a lead screw that maches the one you already have
• 1X pom T8 nut
• 2X 8mm linear bearings (40mm long work better than 20mm)
• 1X stepper mottor 
• 2X 20mm m5 screws to secure the clamp on the aluminum bed
• t nuts for the linear rod clamps and mottor holder
• m3 screws for the lead screw nut and the stepper
• m5 screws to hold the stepper motor
• 5mm to 8mm stepper coupling

Printing settings:

Filament: Petg-cf works best for me (used pla for a bit and still worked well)
Infill: 40% gyroid
Top/Bottom layers: 4/5
Parameters: 4
Supports: on, classic snug works best

Orca slicer:
precise wall on
 

How to install:

1. Press fit the bearings into the printed part (it SHOULD be a bit hard)
2. Screw in the nut
3. Insert the clamping side on the underside of the bed (the side with a big hexagon), dont screw for now
4. install the clamps loosely (142mm between the rods - 15cm between their centers)
5. push the rods through the clamps and the support structure
6. tighten the screws under the bed
7. move the bed up and down, so it can align properly
8. tighten the clamp screws
9. install the stepper motor with the coupling between the rods
10. add the screw (look at the bed, it shouldnt bend at all)

Feel free to ask questions, change the model and upgrade it for your needs