I printed a selection of fan ducts for my Mendel90. Some of them didn't fit and others just didn't work, so I designed my own. I have copied some of the best features from other designs and merged them into a model that will fit on the Mendel90 using a couple of adapters for mounting.
Update - April 2013 - my original fan duct was getting a little overheated so I finally got around to redesigning a slightly longer version which centres the nozzle better.
Update 2 - the all-metal E3D hot end needs a cooling fan and shroud fitted to it. There was not enough space to fit this so I have released an updated low-profile version at http://www.thingiverse.com/thing:91931
The fan duct will end up sitting quite close to the hot end so should be printed in ABS.
The Mendel90 X carriage has no fan mounting points so I decided to adapt my Wade's Block Riser thing (needed for the herringbone gears) to provide two mounting holes for the fan duct. This is a quick and dirty hack designed to allow me to get the fan working quickly. The whole design can definitely be improved and should be consider a work in progress.
Screw the 60 mm fan to the duct with short self-tapping screws.
Bolt the fan duct to the bracket.
Fix the bracket to the riser plate with two more bolts.
I didn't have a spare controller pin on my Sanguinololu (since adding the LCD panel and click controller) so I bought a Zalman Single Fan Controller from Amazon for Ã‚Â£4 to control the fan speed manually. The long ribbon cable provided rides piggybacked onto the main X-ribbon and the controller is stuck to the side of the X motor block.
Future improvements planned include redesigning the riser plate to lock under the X belt clamp and adjusting the duct shape to get the nozzle centred better in the ring.