A8 "EvenFlow" fan duct

thingiverse

This fan duct will be especially useful for PETG printing, where you require less cooling but more control over it. I recommend adjusting your end G-code so the fan runs at least 20% after the print is finished, but the nozzle is still very hot; otherwise, the duct could deform from radiated heat. This is what I use as part of my end G-code, after parking the extruder head: M106 S204; Fan to 80% to prevent duct melting and cool down hotend M109 R50; Wait for hotend temperature to drop to 50°C M104 S0; Hotend off M107; Fan off Many fan ducts increase flow velocity, but this comes at the cost of flow restriction. I was inspired by the original Prusa i3 MK3S fan duct, where you can see a little "flap" that directs the flow level with the platform, but there is virtually no flow restriction. I came up with my own design, which should provide better flow control. V1 has a simple shape and seems to work just fine. V2 has a wider outlet and an inner slat to direct more flow to the lower layer. V3 improved the inner shape to make a smooth transition from the fan to the shroud. V12 only features a lower channel with a smooth transition from the fan outlet, good for PLA. When Z = 0, the duct is nearly touching the platform, so depending on your print quality, you might need to use sandpaper and sand the bottom of the duct flat.