After installing the E3Dv6 hot-end on my Da Vinci 1.0 printer using my thingie:707530, the next logical step was to create a suitable active layer cooling fan for PLA (and also for ABS, when it's really necessary).
While initially I attempted to modify some of the already existing designs, with varying degree of success, eventually I figured that it'd be better to start from scratch and model a custom fan duct that would blow as close as possible to the nozzle tip, rather than all over the bed.
So I came up with this design, which uses a 50mm 5v fan that you can power using the wiring of the stock extruder fan (while powering the E3D's fan directly from some 12v input source), in order to be able to control its speed via gcode. I haven't run any tests to compare it against other layer cooling designs but it seems to have a pretty nice airflow. I'm quite impressed!
Additionally, this model doubles as a stabilizer for the extruder, since it's designed to fit tight under the stepper motor, acting as a sort of wedge that further strengthens the set.
This model is FDM friendly and can be printed as-is, without additional support structures, when lying on its flat side (where the fan is attached). There are some challenging overhang angles, but nothing that cannot be done by a correctly dialed in printer. Only the opening near the tip, which is used to slide the belt in, requires of support, but I've already added custom supports to the model.
I printed mine on ABS, at 0.2mm, 30 mm/s, 50% infill. Once printed, push the belt down a little to make room while inserting the duct on its position. Then gently twist and slide the belt in through the opening. Move the print head left and right several times to ensure that there is no contact with the belt or with the rod. Otherwise use a small file or sand paper where necessary.
Optionally you may also cover the opening with a piece of kapton tape or similar (as you can see I did on my pics).
Note that this fan duct has a clearance of only about 1 to 1.5mm when the bed is at Z = 0. That means that the screws used to secure the contact pads on the front corners of the bed will make contact with it when printing near that area. So if you plan on using this model you should really consider either replacing those two screws with some lower profile ones or -as I did- go with the far cheaper and simpler but equally effective workaround of replacing them with zip-ties :) This is shown in some of the pictures.
Also consider that if you are printing something that curls up significantly, then there is also a chance that the duct will hit it and potentially cause some damage.