It's a very interesting project. I tried to build a similar device some time ago, though with little success. It sort of worked but it's working envelope was simply too small compared to the size of machine. Now I think it might have something to do with joint angle, which was 45 degrees (seemed like a logical choice at the time). Yours are more like 30 degrees. Have you came up with some kind of formula for joint angles to maximize working envelope?
Also, could you, please, publish Fusion 360 files?