When last we heard from our intrepid robot, all three stages were almost built. Only the right way to keep the Z-stage from falling was missing, but a move had interrupted further building. Since then, another move has occurred, but things are now calmed down enough that I have been able to join FabLab München, the local maker group.
They have taken me and my robot in and kindly lent me the bits and pieces I hadn't brought over yet. The drivers have been re-tested and now all work. The threaded rods have been oiled (this helped the X-stage quite a bit), and a solution for the dropping Z-stage has been found: Place a ball bearing on a block underneath, so it is supported without getting extra resistance. This has been implemented (with several layers of cardboard:), and the last few kinks of the Z-stage are being worked out, mainly bolts that are too long.
I have decided to not go the purist way and rather have the extruder head printed on one of the other machines (if they work by then). Especially since there's hardly any designs for non-printed extruder heads out there. Maybe, once all the other problems are worked out, and I know a little more, I will go back and make it pure. Maybe.
In the meanwhile, it has so happened that I have inherited a broken MakerBot. Some of the electronics smoked, and we're not sure which. Since the owner has moved on to other robots, he's happy to let me try to fix it and get it running. Sweet!