I've not been totally happy with the fan duct. It great at directing air to the front of the piece you are printing, but not enough air reaches the back. This sometimes shows up as pieces sagging as they are too hot, or curling up for the same reason. Curling up is bad as the print head may then collide with the curled-up edge and bad things then happen.
I have a hacked up a replacement which directs the air more evenly around the hot end. It is very ugly at present, and I will try to refine it further. It's at www.thingiverse.com/thing:1707416. I don't have great CAD skills, and I just loaded the STL into blender, sliced some bits off and attached some new bits. If I have the time, I'll try to make it cover more area, and use curves rather than all being rectilinear. Like I say, it's a hack.
To show the effect, here are some prints of Marvin with the original and modified versions. The first picture shows 0.05mm and 0.1mm layer height prints, and you can see poor quality on the back of the print, furthest from the original fan duct. The second shows 0.1mm with the new duct and it's a lot better, though still with some room for improvement.
Wow, that's a very noticeable improvement. I've had that issue too. Looks like I'll be working on getting a new duct designed (I'm using my own designed gantry which uses a different duct design, otherwise I'd try yours). Thanks for contributing the idea and evidence.
I have this idea, to make it (sorry bad english) 8 sided, with air comming out of 4 sides (and 3 sides with no air comming out, and one side cut out, and closed. so we can see the nozzle from the front, thru the fanschroud.
IT professional farther of 2 great kids.
tinkering with 3d printers, design, cars, campers, and alot of other things :-)
I just printed this to try it out since my print head temps were dropping with the fan on. I printed it in PETG and it seems like the top of the horns need to have a little thicker walls, but other than that it seems to print well. I used masking take to seal the thin walls on top of the horns which let me also decrease the slot side on the horn closest to the main duct which evened the air flow significantly. Before if I set my extruder temp to 242, it would hit 242°C and drop to 215°C when the fan turned on at 100%. Now the temp only drops by 2°C at 100%. Awesome job!
One problem with the design is that the right hand horn tends to sag a bit over time, not surprising as it's not very strongly supported and next to a source of heat! I may look at tweaking the design to see if I can improve it.