Both Tekma3D and New Matter both came out with printers that use crossed splines to drive the x and y of their printers. (link below if you are interested) They both are in the process of trying to acquire a patent on the technology. Being the open source hippie that I am, here is a system that is functionally the same but should give a wide berth to the patents.
Youtube Candy
TO BE CLEAR, I don't think this kind of system (screw or spline) is very good. I do think it is fun to watch.
If the system has opposing racks as shown, one screw should be left handed and the other should be right handed. (I messed up modelling it and they are both left handed. It will still work but the math isn't as nice and the resolution isn't the same in all directions.) If all the racks face the same way, like the MOD-T, then you can use two left handed screws. The system is driven just like a CoreXY system.
The screw should also have a fairly large travel. The screws in the video are 1/2x8-8start ACME screws so there is 1 inch of travel per rotation.
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ConceptFORGE
Wally,
GUS Simpson,
LISA Simpson,
THOR Simpson,
Sextupteron,
CoreXZ