Why we wanted it A stock Ultimaker comes with a single extrusion head fixed to the X and Y axes. As we were experimenting with dual extrusion printing, modifying this design became increasingly inconvenient and time-consuming. To make developing the hardware-side of our multihead printing much easier, we decided to split the extruder head design into two indendent hardware parts. The 'frame' part is fixed to the X and Y axes and thus determines the head's location. To this frame, up to 4 'cassettes' can be attached. A cassette is flexible: it can hold a regular PLA extruder head, but can also contain a syringe, fan, equipment, etc. The cassettes are height-adjustable mounted to the frame.(1) Frame Our first working prototype of the frame is cross-shaped plywood fortified with some regular M3 screws. The screws ensure that the frame is tightly fixed, so that no undesired vertical movement takes place. The bearings are not clearly visible, but are mounted inside. Relative to the stock extruder head, this frame is only 1 cm wider on each side (now 69x69 mm). The vertical slots on all insides of the cross are to connect a cassette unit, and allows to adjust each cassette height vertically.(2) Cassette The extrusion part of the stock Ultimaker head has been moved to cassettes: small wooden parts that can be attached to the frame. Given the frame's cross-shape, up to four cassettes can be added to each frame. Our current extruder cassette prototypes are 27 x 31 x 60 mm (l x w x h) but can be customized at will. Two openings in the cassette allow it to be mounted to the frame with regular 12mm M3 screws at the desired height. As mentioned above, the cassettes can be replaced by anything you'd like to attach.We have successfully mounted two cassettes, each holding a PLA hot extrusion nozzle, and could make our first dual extrusion prints (later more on this). Currently, we're working on a 'fan' cassette to deliver (hot?) air to the hot nozzles and remove the need to mount a fan to the head itself; and we're looking into gel printing. More to come!(Developed at Protospace Utrecht with help from Douwe van der Veen)With a lasercutter, things can't be much simpler than doing this:Note: no aluminium plate needed in our experience. The 6 mm wood works well enough, and the cassettes are sturdy enough to resist bending.