Currently the prototype can produce prints, but there are serious defects in the motion system. Most notably, the pinion gears do not stay still on the stepper motor shafts. This inconsistent wobble distorts print lines, especially when travelling diagonally. Here's a video of the x-y gantry in motion.

Hard to see the wobble here, but it was quite apparent in the first few test prints, and became worse with time. 

To fix this, I'm going to reduce the size of the pinion gear and lasercut a series of these gears with varying internal diameter. I cant easily control the kerf-width of the lasercutter (at least down to the tolerance needed for a press fit), but a rough estimate would be ~0.3mm. To cover this range, I'll lasercut a series of gears with ID 5mm +- 0.3, 0.2, 0.1 and see what fits. Should get around to it in a day or two. :)