I wanted to design a quick and easy fan mount that could be printed on the stock ridigbot without support material. This is designed to work with a 40mm fan, and 15mm-18mm m3-0.5 screws, although alternate fasteners will work.
Please let me know of issues or improvements with this build, I've made some modifications since the last version (which is the one I printed) and am hoping they don't cause any issues.
This model is inspired by and based on jwolee's also excellent rigidbot fan mount. http://www.thingiverse.com/thing:407430
For this build, you'll also need: 4x m3-0.5 machine screws in 15mm-18mm length, or some other way to fasten the two parts of the build together (like glue), and a way to attach the fan (zipties, more glue).
Attach the fan to the top of the funnel using 2 m3 screws (with moderate force, you should be able to self tap the machine screws (or use a tapping bit), otherwise there is room for a nut on the other side. Alternatively, glue or zip ties could be used to mount the fan. (But make sure you check your fan orientation before you attach anything permanently!)
Attach the funnel part to the bracket with m3 screws. When oriented in its final position, the funnel should be on top of the bracket, with the sloped top of the bracket touching the underside of the funnel. This attachment point should be solid and the connection flush, otherwise there may be issues with the fan scraping the print bed and / or damaging your prints.
Attach the assembly to the front of your extruder. Unscrew the two m3 hex screws on the left side of the extruder baseplate that attach it to the gantry. Line up, and reattach with the bracket on top of the baseplate.
Attach the fan connector to the unused fan1 slot on the extuder head and perform general wire management. Your fan should be ready to use, and is controlled by your slicer program.