Update 11/12/2019: New version of threaded rod mount

Update 11/11/2019: New version of belt tensioning mechanism. Adapter misalignment seen on pictures is fixed.

Update 10-22-2019: New motor mount with adjustable belt tension.

My sizes:

x axis 3030 extrusion - 420mm
y axis 3030 extrusion - 410mm

For this I use 1220mm closed loop belt belt.

Update 10-11-2018: Added better bottom threaded rod mount. Use 4 30mm screws to clamp bearings together to eliminate up/down z rod play.

I made dual z lead screw mount driven by single stepper motor. Unfortunately it is not universal for all frame sizes. But using only a browser and basic cad skills you can easily adjust it. I use this setup and it is working perfectly. Only 3030 extrusion size is supported. If there is no space on the bottom you can mount motor upside down.

Important! Before printing you should probably adjust the design due to different belt length and belt angles.

There are the steps to adjust:

1) Register at https://cad.onshape.com, it is free. It is online CAD and it is very easy to use.
2) Open link to my design: https://cad.onshape.com/documents/cb42126c5a73a6d564db4cee/w/82ac277851ad018c6e526d38/e/716eec5e1d551a3781f9b153
3) Click on hamburger and select copy workspace. This creates your own copy of design and you will be able to edit.
3) Go to 'reference' tab and select (double click) the sketch 'reference' in features list.
4) Here you can edit dimensions of your printer (x extrusion length and y extrusion length). Also check distance from extrusion to z axis lead screws and lead screws y position.
5) Go to dual z mount tab. Select 'belt length measue' sketch. Make sure the sketch is fully visible. Drag select everything and you will get required belt length in the right bottom corner of the screen.

Note! The length of the belt can be adjusted about -+1cm by moving stepper motor.

If you can not find belt required try to modify 'reference' sketch again or the design itself. Basic knowledge of cad software may be required.
6) Check all the tabs and all the parts in Parts section. Right click on each part and click export. Export all of them to .stl and print.

BOM
[ ] GT2 Belt (For my 400mmx400mm x and y extrusion the length is 1140mm)
[ ] 2x 36T GT2 pulley 8mm bore toothed
[ ] 2x 20T GT2 idler toothed
[ ] 1x 20T GT2 idler not toothed
[ ] 1x NEMA17 stepper motor
[ ] 6x 608 bearings (to support z axis, may be 4x will be enough)
[ ] 13x m5x10mm (for mounting)
[ ] 13x m5 hammer nuts
[ ] 4x m3x25 screws (They are shafts for idlers)
[ ] 4x m3 nuts
[ ] 4x m3x15mm screws for nema17 mount
[ ] 2x lead screws

Source: https://cad.onshape.com/documents/cb42126c5a73a6d564db4cee/w/82ac277851ad018c6e526d38/e/716eec5e1d551a3781f9b153

CR-10

No

Yes

.2

30