This is my attempt at creating a custom mount for a 60 mm fan (eg. Noctua NF-A6x25 5V) with the possibility of tuning the airflow to the nozzle for filament cooling.
It is composed by an "IN block" an "OUT block" and a "gate". The gate is inserted in the out-block (a bit of sanding may be required), then the out and the in blocks are glued together, the alignment is made straightforward by centering holes.
The in-block splits the flow in three, to the top, central and bottom part of the extruder. The opening of the latter is controlled by the gate which can easily be adjusted to 5 positions: 0%, 25%, 50%, 75%, 100% opening. The flow directed to the nozzle benefits from a toroidal opening, which is compatible with the given pipe wrench for the nozzle removal.
Before mounting the fan, the full assembly should be screwed to the extruder by using the original screws and mounting holes. Then the fan can be added, I used the screws given with the fan.
Note that the Noctua cable can be directly plugged into the Cetus fan slot, provided some sanding to reduce its size (please be carefull with the polarity of the cables).
I modelled this with OpenSCAD, but the sources are quite messy, so I am only publishing the rendered stl.
0.15 layer with 0.4 nozzle