This is just a crazy idea at this point, but I wanted to organize my thoughts here. What if the Mendel was redesigned to have a stationary extruder that only moves up and down while the build platform moves X and Y like the MakerBot? One or more extruders could be anchored perhaps on one corner of the frame. The Y axis build area would be reduced by about a half, but since there would be no Z axis bars in the way - the X axis could be doubled (or more!) in size and you'd have a rectangular bed instead of square. If viewed like a MakerBot, the side would become the front and it might be more logical to swap the X/Y axis names.
- Z axis would be driven by a single lead screw and 2 rods like the MakerBot Thing-O-Matic, which should allow faster Z speed - less blobs
- fewer bearings
- potentially much larger overall build area, particularly if the extruder could be mounted in center instead of the corner
- since the extruder is only moving up and down, multiple extruders would be easier to implement since you don't have to move a heavy weight around
- Z axis height should be improved since less of a chance of colliding with frame, especially if you remove the electronics plate and use more compact controller like RAMPS mounted on bottom of machine
- although the machine itself would remain basically the same size, the X axis would extend out of the sides quite a bit which would make the operating footprint larger and a little awkward (would be lessened if I can think of a good way to mount the extruder closer to the center instead of the corner)
- not sure how the frame stability would be affected by removing the Z bars (maybe strengthened by crossbars?)