I found that I needed extra cooling on my J-Head mk4 hot end, so I designed this duct to add a 30mm fan to the Mendel90. This part fits inside Wingmaster's square fan duct (http://www.thingiverse.com/thing:657540) and tucks neatly under the X-carriage. Simply glue in place and add a fan with four #2 screws. I've also added a version with two fans, for extra cooling power, but I haven't tried it myself as one seems to be enough. It may interfere with homing in the x-direction - if you try it, let me know.Print the part however you like, but don't use support as it will fill the duct. Glue into the existing fan duct, and install the fan. You must have a fan duct with a square hole from http://www.thingiverse.com/thing:657540, not the default round one.