To avoid Z-height differences between left and right side of the bed I set up an interlockiong mechanism between both threaded rods.
The pulleys are all made using F625ZZ bearings. Longer bolts through the pulley are M5x30 and are fixed in the 2040-profile.
You will need :
a long GT2 loop that I ordered from Adafruit
2x500mm of 2020 profile to carry the rods
1x500mm 2040 profile for the steppers
2x straight metal stepper supports
4 x 100mm 2020 pieces to receive the 2 larger 2020 pieces and some corner pieces to fix all 20xx to the chassis
2 extra GT2 pulleys for the threaded rods (8mm internal diameter)
sufficient time and some engineering skills are recommended.
Lower the Y-rails until they match with the top of the steel rods. Keep a couple of mm between the rods and the profile.
Install the rods with supports (and the bed!) without fixing them Don't forget to get the timing belts over the threaded rods on beforehand!!!
With the rods in place run the bed to the top position and fix the top supports to the 2020-profile.
Run the bed to the bottom position and align the supports AND the supporting 2020-profiles do this a couple of times until everything runs smooth.
Fix all supports.
Install the stepper.
Install the pullleys on the 2040 profile with a 80mm 2020 profile.
Run the long belt along its path. Loosen the locking screws on the GT2 pulleys on the threaded rods and adjust tension with one of the pulleys on the 2040 profile. DO NOT overtension!
Adjust both sides of the bed measuring from the bed to a point on the X-gantry.
Fix the locking screws of the GT2-pulleys.
A live view in this video