Opinion on cooling fans

[MorbidSlowBurn]

I have seen a couple of people mounting fans on the hot end platform. I understand there are two reasons for this. One is the keep the PEEK part of the extruder cool and the other is to cool the part as it is being printed.

My question is what is the opinion on the impacts of the fans. Is there an affect on print quality. Does it have any significant effect on the print head movement e.g. Added weight, gyroscopic effects ...

What size fan is good? Reccommended cfm? Use a fan tube to guide the air to the wanted location or just mount the fan without any air "guides".

Also since the Rambo board has fan control built in, should it be used so small parts are cooled more but have less cooling on larger parts?

[mhackney]

Although it might be possible to pull double duty for one fan it is really best to have a dedicated fan for each function. My opinion is that people way overdo it on fan size. Read my build thread and I have actually taken temperature measurements of the PEEK tube with and without a fan. And this is a 25mm fan directed right at the PEEK tube. The advantage of this is you are not also cooling the nozzle. I assert you want the PEEK barrel cool, the nozzle hot and for some parts and materials, the part cool. Once you have the barrel fan setup, may as well use it for everything. I find I have a lot fewer problems with plugging with ABS and a barrel fan is an absolute necessity for PLA.

The, there are cases where you can benefit from a fan cooling the part. The calibration pyramid for instance. The small width pillars do not have a chance to cool and consequently can warp and bend. A fan assures cooling/solidification of the plastic. So yes, it does affect print quality. But again, I believe many use fans that are too large for this purpose too. I use a single 25mm fan directed right below the nozzle. This fan is the one controlled by the RAMBo so it can be turned on and off via gcode when needed for instance, it is usually not a good idea to have the fan on when putting down the first layer. It can actually prevent it from sticking. I don't turn on the fan until layer 3 or more. For large sparsely filled parts a fan is probably not needed. For small and or solid filled parts, a fan can prevent warping/distortion because the part doesn't have time to cool.

These small 25mm fans are very light and do not have an observable effect on print head movement. For the barrel you don't need or want a duct with these small fans, they direct the perfect amount of air flow around the barrel. I do think there might be advantage of ducting to have a more direct beam of air for part cooling. I have not had time to work on something for that yet.