One of the most effective addons for my Mini Kossel: To achieve good results when printing PLA, especially with lots of overhangs or bridges, a dedicated layer fan is essential. I've designed this one in order to replace Johann's original design. And, well - it works like a charm. :-) Four/five versions are available: "-fin.stl" is the same as the basic Version but with a fin for the PEEK fan. The fin is not really needed there (regarding the aerodynamics). It acts more like a supporting structure to make printing more easy. However, the fins inside the ducts for the layer fans have the task to lower turbulences of the air plus to lower that annoying siren-like sound of the 9.000 rp/m fans. "-Type2" has standard 50° nozzles, no fin for the PEEK fan and two additional mounting blocks on the backside for future use (for a proximity sensor for auto leveling: http://www.thingiverse.com/thing:843585). "-35deg-bend.stl" has nozzles with 35° bending. :-) "-long.stl" has longer air nozzles (45°, 15 mm height) and should only be used with the longer J-Head clones from the far east. I'm printing with the 50° version "Effektor-Basis2-Type2" with great success. That's it. Have fun. :-) I've printed mine with ABS at 0.1 mm layer height @ 233°C, no supports and 35% infill. I recommend using one 30mm x 10mm fan for cooling the J-Head and two 30mm x 20mm or 30 x 10mm high airflow fans for layer cooling.