Found the actual reason why MK2Dollo made that artifact on the Nefertiti bust: the bed carriage was bumping on the ziptie that holds the smooth rod in place. Not sure why, might be that I've slightly mispositioned the bearings too deep on the carriage.
Fixed this by rising the bearings 2mm on the bed carriage model. For the already printed parts, I made spacers. Also fixed the y belt holder more firmly on the bed carriage so printing ABS should be possible again.
2019-01-30 18.42.25.jpg2019-01-30 18.42.33-1.jpg

For the Dollo rebuild, need to print quite a lot of extension parts and 4 corners. Bed carriage needs 8 and there's pieces missing from the frame. Also as I'm planning on using the full length of the 505mm threaded rods, I need to replace 4 60mm pieces from the corners. Ran out of black filament, now waiting for my order to arrive.
Also as I'm going to reuse the z-rails, I need to modify some of the bed carriage/z parts. And there's also some bugs that I need to fix so some modeling work to do.

Currently the max viable print dimensions should something like this: 320x320x450mm. Which means I need to get a bigger bed. I have some 3mm aluminum, just need to get heater for it. Or multiple heaters, I wonder how hard it would be to make a sectioned bed...