Summary

Note: I wound up making a third version that I'm using now. (http://www.thingiverse.com/thing:228536)

Improved version of my previous fan holder (http://www.thingiverse.com/thing:213416) :

Mount now has adjustment in 3 axes to accurately position the nozzle.
Exit nozzle surrounds hot end tip.
Nut detents in cowling.

Holds a 60x60x10mm fan (I'll probably make a 40x40 adapter).

Instructions

Ironically, you will almost certainly need a print cooling fan to print the nozzle. It will help with the cowling too.

All parts were printed without support material. The internal fins in the exit end of the cowling and in the nozzle are primarily there to provide some support points for the bridging when printed (and they look cool too).

I printed the cowling rotated 30ÃÂÃÂ° so the exit end and fins were aligned with the X and Y axes; it looked like the slicer used a better bridging pattern in that orientation. Same thing with the nozzle.

The separate mount parts are "cut" from a single solid, so they're exactly the same size; they'll probably need a little scraping cleanup with a knife to fit together. That's ok, because you want the mount to be a tight fit; once the adjustments are set, you don't want it to move.

The nozzle is designed to snap onto the cowling. I didn't get very true-to-design clips on the nozzle print; it needed some work with a dremel to clean them out so they would snap onto the cowling.

The nozzle is designed to snap onto the cowling. I didn't get very true-to-design clips on the nozzle print; it needed some work with a dremel to clean them out so they would snap onto the cowling.

I tried using netfabb to (re)save the cowl .stl file as non-ASCII (which was much smaller), but the slicer messed up using that file, so I uploaded the ASCII one.

Extrusion cooling fan-holder/cowling for MakerFarm Prusa i3 - Version 2