this was designed because the hotend's fan sucked in hot air from the print surface and kept cooling the printbed too much. Fits on E3D V6 30mm Fan.
yet, I used some tape to guide the airflow, but it looks much more professional this way :)  
note: all angles off the Z-axis are max. 45° to keep it printable. the wall thickness of this part is 0.8mm to get a good print with two perimeters out of my 0.4 nozzle. Let me know if you need a thinner/thicker wall.
*Update 18 Okt. 2015: Added a new file for 40mm Fans