Fan

What is the purpose of the fan on the extruder head if its purpose isn't to cool the heated barrel?

It is there to cool the workpiece down. When you use low melting point plastics like PCL you need to cool the object being built to solidify the layer before the next layer is put down.

The same is true of higher melting point plastics when the object is very small.

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[www.hydraraptor.blogspot.com]

Hi nophead -- Ah, I actually got that question from reading your blog ("When the filament is pulled back out only a few millimetres has expanded at the end. In contrast, without the fan the filament swelled most of the way to the top and jammed."). So it looks like the larger clear fan is limiting the ABS swelling.

You have 2 fans -- one small black one that looks to be shooting air into your "heatsink" or onto your heated barrel (I can't totally tell from the picture) and the clear one shooting down onto your workpiece. The clear one I get, but what about the small black one. I think that's the one you refer to when you say "With the nozzle at 240

Yes the small fan is a new development for making the hot cold transition in the extruder barrel as short as possible. I think I will be able to eliminate it by using a better heatsink and replacing the PTFE section with a thin walled section of stainless steel pipe as in Larry_P's design [repstrap-cerberus.blogspot.com].

The advantage of SS as an insulator is that it is rigid so does not need the bolts, which is were most of the heat is conducted in my design.

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[www.hydraraptor.blogspot.com]