I wanted to have my printer very silent, so after changing my driver to the famous TMC2208, i was annoyed by the noisy extruder blower. So i did change it from the default 404010mm fan to a 606020mm fan, buuuut the rods were blocked by the new fan :(.
So i design this duct fan in order to mount it properly and without blocking the rods.
It does fit well and the noise level is very good.
It's still a bit noisier than the 60mm without the duct (which block the rods), but still very very silent !
(i do have a small server in the room which do little noise and we do only here this one from now on).
I did print it in PLA, and it's working fine.
You have to use rafts or brim to make sure it's stay in place (i did print it vertically, the 60mm top)