This is a way to sync the Z-axis drive using a single motor.

Printed parts:

• plateL.stl - top left plate, the motor and idler are mounted here
• plateR.stl - top right plate, essentially a mirror image of the left plate, but without the motor and pulley.
• rod_plug.stl (print 2) - replaces the original guiding rod plugs on top plates
• rod_holder.stl (print 2) - holds the guiding rods from below, since the motors aren't there anymore
• tube_guard.stl (optional) - keeps my bowden tube from interfering with the timing belt

If you prefer the motor on the right, you can print mirror images of the plateL.stl and plateR.stl.

Hardware needed:

• use the original 4 M3 screws and nuts to mount the top plates
• 976mm 488 teeth GT2 (6mm) closed belt (https://www.aliexpress.com/item/Hot-sales-GT2-timing-belt-976-2GT-6-length-976mm-width-6mm-teeth-488-for-3D/32299312364.html)
• GT2 18 teeth pulley 5mm bore - mounted on the motor (https://www.aliexpress.com/item/3d-printer-2GT-GT2-Timing-Pulley-18-teeth-Alumium-Bore-5mm-for-GT2-Belt-Width-6mm/32835852375.html)
• 2x flange bearings 8mm bore (https://www.aliexpress.com/item/8mm-Bearing-Zinc-Alloy-Miniature-Bearing-Pedestal-KFL08-Flange-Pillow-Block-Bearing-diy-cnc-parts/32773248332.html)
• 2x GT2 36teeth timing pulleys with 8mm bore (https://www.aliexpress.com/item/3d-printer-pulley-aluminum-timing-pulley-2GT-36teeth-bore-5mm-6mm-6-35mm-8mm-10mm-pulley/32658350983.html)
• 1x idler pulley for GT2, 5mm bore - (https://www.aliexpress.com/item/Timing-Gear-Pulley-Without-tooth-Idle-Pulley-synchronous-Round-5mm-For-GT2-Belt-Width-6MM-Power/32761426168.html)
• M8 rod, length 349mm - needed to stiffen the frame, because the frame is too flimsy to withstand the timing belt tension
• 4x M8 nuts and washers to fix the M8 rod
• 4x M5 25mm screws and nuts and washers - to fix the flange bearings
• 1x M5 40mm screw and 2x M5 nuts and a washer - to mount the pulley idler
• 2x M3 20mm screws and nuts for the top rod plugs
• 4x M3 15mm screws and nuts to mount the bottom rod holders
• 4x M3 12mm screws and washers for motor mounting

The mounting holes for the flange bearings are a bit oversized so you can keep the leadscrews and the guiding rods parallel. The way I did it:

1. Mount the flange bearing without tightening the mounting screws
2. fix the leadscrews in the bearings
3. bring the X-axis assembly (the one that rides on the leadscrews and rods) all the way up (maximal expected Z height)
4. ensure that the leadscrews are parallel to the guiding rods (I eyeballed it, by keeping the bottom of the leadscrews above the Z motor axes, which were yet unmounted at this stage).
5. tighten the flange bearing mounting screws

Don't forget to change the steps/mm parameter for the z axis (from the original 400 to 800)

Hope I included everything here. If you find anything missing, please comment and I'll answer/update.

Anet A8

Yes

0.2mm

20%