A simple parametric fanduct adapter to mount Noctua fans on the stock E3D v6 fan holder that snaps around the heatsink.
You can change the total length of the fanduct, and it has X/Y offsets for the 40mm fanside, not the best parametric model ever, but I simply wanted a short and smooth fanduct.
Tested with a 1mm offset, without offset, at default size (12mm total) and at +5mm extra length, both with the A4x10 & A4x20 FLX noctua fans, the 10mm didn't give me heatcreeps on PLA prints at 210-215-220°c but I needed this : https://www.thingiverse.com/thing:432630 in order for the A4x10 to have enough air pressure tho. This is not a fan cover and should be placed AFTER the fan : (fan)>(laminar flow plate)>(30mm fan snap thing); this laminar flow plate is not needed for the A4x20.
Note: E3D V6 hotends and Noctua fans have a love/hate relationship, It was fine for me with a A4x10 but I expect summer to push it to its limit, so I went for the A4x20 just in case.
A bigger and less restricted airflow (so... a bigger fan mount) is the best option so far, but this gets the job done 'til someone design the perfect mod / e3d carriage :)
Note2 : It's best to print it at a low layer height, 0.1 / 0.12mm recommended.
Made based on : https://grabcad.com/library/e3d-30mm-to-40mm-fan-adapter-1