https://youtu.be/MNZOPV5nO94The magnetic change idea is from "foehnsturm" I redesigned it for the Ultimaker2. My goal was to stay close to the UM2 design, you can of course change this and add f.e. a full metal head as 2th head.The main advantage of this setup is that you can easy put the 2th head aside and reclaim most of the buildarea for single head extrusion.Another + is the use of different nozzle temperatures in the different heads.The main issue is the leaking of filament from the 2th extruder. Using retraction and a prime tower does help a lot. At least in this setup the leaking does not take place on the printed part.you'll need left and right parts, just mirror the items in your slicer.find a project summary including instructions here;http://ultimaker.com/en/modifications-and-hacks/view/10657-multi-extruder?page=27#reply-107302update 25/5/2015: Added the "pick up" unit that I forgot in the first upload, also corrected this in the step file.update: added new version of the docking corners that clamp to the housing, so no need for tape anymore. (all the parts with the name starting with "non-tape")