I took the original Mini Kossel carriage and just replaced the traxxis ball joint mounts with the Rostock/Rostock Mini universal joints, which are completely printable aside from the rods and screws and have been noted (by Johann) to have less slop than traxxis ball joints. Edit: They get sloppy rather quickly using ABS and PLA in my experience so far, some nylon screws or smooth rod fixed in place may solve this. I have an awesome new ball joint design coming very soon anyway! :) I made a few different carriage styles, one for GT2 belts and 4 different spectra style mounts to suit your configuration or preferences. For spectra the vertical line mount is for an adjustable line tension screw, use an M3 screw (10-15 mm) with a washer, put a slip knot in the spectra & snug it up to the washer & install the screw, it should tap it's own threads no problem. I've also added in a spot for an adjustable end-stop triggering screw but it's best to just let the top of the carriage trigger the endstop and perform all endstop offsets in software; this is what I do now. If you need to modify any design I've also included the OpenSCAD files. If you're using this on the Kossel carriage use 3 * M3x20mm screws and M3 nuts to fasten to to roller truck.Use the original Rostock mini printed u-joints, jaws and effector in the zip file attached and follow the build instructions here: http://reprap.org/wiki/Rostock_mini#Carriage These work great with my other mod, Carriage Roller Base for Kossel & Mini Kossel w/ OpenBuilds 2020 V-Slot Extrusion & Mini V Wheels: https://www.youmagine.com/designs/carriage-roller-base-for-kossel-w-openbuilds-2020-v-slot-extrusion-mini-v-wheels Credits go to Johann Rocholl for the original source files.