This is my attempt to make a fan shroud to maximize the airflow from the 40mm fan. I still think the airflow is too forward biased; hopefully further revisions can help make the airflow more even.

I have only used PLA so far. I realize ABS should create a more temperature resistant model. I highly recommend using ABS if you print at temperatures above PLA or remove the shroud all together for higher temperatures. I just started printing ABS ~235C, heated bed 100C and the bottom of the shroud is sagging. Also be careful not to remove the fan while it is running; I read somewhere that can damage your board.

The print gets rough around the top half of the fan mount. I used 0.254mm layer height @ 30mm/s print (70mm/s travel). The tolerances are pretty tight around the nozzle; the parameters are adjustable in the openscad file if you can find them :)

The openscad file is messy. I will be uploading a cleaner copy in the near future.

**UPDATED

Added cleaner V1a scad file

V1b has better directional flow but is too restrictive. Added a buffer for the fit by the fan.