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Gravity Fed Extruder for 3mm Filament

by ronthomp, published

Gravity Fed Extruder for 3mm Filament by ronthomp Apr 8, 2012
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This is an experiment in making 3mm filament for my 3d printers.
While it did extrude, more work is needed.
Read more about it and see larger photos here:


There are no instructions, yet.
This is somewhat inspired by the recyclebot, but this is intended to use commercial pellets, at least at first. I was making this to use the auger feed when inspiration struck.

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Water cooling would simplify things a lot and you can always do a dry off and then bake in a oven or use water absorbents  to dry the produced filament. Water will enable a  skin to be quickly formed locking the diameter  Besides it only needs to cool down and then be  dried and rolled up a matter of seconds, There wouldn't be that serious an amount of water impact in that time frame. Of course you need to then dry it of for best performance. The above design direction is no god for other reasons, first you have a large amount of  plastic with poor mixing so you get solid s and partial melt  and you will get crystallisation if it sits there  for a long time producing poor product that fractures and lacks strength. The screw extruder idea is neded  and a design with a  flow valve arrestor. I dont think a conventional   spiral wood drill will work as well as a  specially ground  exstruder but possibly

As I understand the key to constant filament diameter is get consistent force driving the plastic through the whole extrusion. I have seen a plunger based version of this before and they had problems with the beginning and ending of the stoke causing inconsistency. In your system I could see that the amount of plastic above the melt point would changing This might change the the driving force with the amount of filament above the melt point as so have a similar problem.

I am not really sure if this issue since the temp might have a much larger effect.

Regardless I love this initial design.

I had some similar thoughs, except never got around to building a test rig... For the filament collector/spooler, my idea was to have a large circular tub of cold water and have an X and Y axis on the filament extruder and to move it in a large circle around the inside of the tub while it extruded. That way you'd end up with a large circular spool of filament without as much trouble from having pullers and the like, which might affect filament diameter.

All still a bit of a thought experiment for me though...

I beleive the hydrophilic nature of PLA, ABS, and PC would make a water-bath a bad idea for cooling. Mineral oil would probably work, though the filament would need to be cleaned at some point afterwards (which would again be difficult without water).

The commercial filament manufacturers actually use a water bath system. As long as the filament is properly dried afterwards it is fine. The mineral oil would actually contaminate the filament where water could be simply dried out of the filament by placing in an oven at 150-200F for a couple hours.

Wow, very interesting. I was working on something that looked pretty similar. Except I was going to try using air pressure to for force the plastic out. Never finished because it kind of seemed like having a closed, pressurized system would be to difficult to add more plastic to melt to. Instead I have been looking for an old style meat grinder to try an auger driven extruder instead. I may have to try a gravity fed setup.