Filament routing for direct extruder
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I recently had a major cloggage event due to brittle filament. I run the filament from a spool to a filament out detector on the printer and then via a approx 600 mm Bowden tube into the extruder. Initial the Bowden tube was selected as I could just route it with all the other stuff that needs to go to the printhead.
As my disaster with the broken filament indicated, there is a big problem if you let the filament sit for two weeks and it happens to get super fragile.
Yes, I could pull the filament out and push it back in for every time I start a printing session but let's face it. I am inherently lazy and am likely to lapse on the unloading/loading routine.
I was thinking that I could just run the filament in the open air directly to the extruder but I am foreseeing a problem. Suppose I have two models loaded, one on the left side and one on the right side on a 500x500 bed. The printer does it's thing on the left side which is where the filament enters the printer. Once done, it hussles it's little butt to the other end but it's used up some of the slack in the filament. SInce it now goes to the far right, it needs a lot more filament to span the distance so as it travels to the right it will hit the point where the filament slack is used up and it now tries to un-spool filament at 200 mm/sec. This will not go over well.So my question: How do you route the filament with a direct extruder setup. Does the filament just flow through the air (remember 500 mm bed) or do you go through a Bowden tube? Is there another option maybe?
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I route mine thru other PTFE tube - it helps constrain and protect the filament as it travels, preventing bends that can snap/snag the filament.
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@luke-slaboratory, yes, that was my original thought. So do you load/unload the filament for every printing session? Have you ever run into the PLA becoming real brittle and mucking things up? I don't think that ABS or PETG is prone to the same issue or at least I have not seen it.
If you do unload the filament, do you just do a small retraction, retract all the way past the extruder or remove it completely out of the tube ? -
@jens55
I do neither, unless its something like Nylon.Normal filaments i leave in the bore for extended periods of time.
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@luke-slaboratory .... hmmmm, maybe this batch of PLA is just no good but the funny thing is that the only fragile section was from roughly the spool to the extruder. It was fine after that.
Thanks!
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@jens55 how old was it/how much of the reel had you used? I recently used up some old half used spools of PLA (one was over 4 years old!) that had gone quite brittle on the outer of the reel, but beneath that it was much better (I won't say good as new...). I've noticed similar things on new filament reels when they've been damp
FWIW, I have a similar setup to you with a direct drive (BMG into Chimera) and a long bowden feed tube, but haven't noticed issues with brittle filament before, even leaving it for several days between prints. I do typically extrude 20mm before doing a filament change though...
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@jens55
I've made rig above the printer which holds the spools. The extruder only has a short 10cm tube on the inlet to act as a shock damper. IMHO it's best to let the filament find it's own way without too much guidance. -
@jens55 I have a similar issue with my 6 input mixing hot end in that I have 3 spools on the left of the printer and 3 on the right. To all intents and purposes, you can think of it as direct drive because the 6 extruders run on a separate gantry above the hot end with only about 150mm of Bowden tube linking the extruders to the hot end. When I get chance, I'll post some pictures so that you can see how I've addressed the problem (btw the printer frame is 600x600.
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I use a bowden tube that has a split in it near the extruder, so more a reverse bowden? The filament spool goes on a spindle on the side and feeds into a bowden tube that's fixed to the frame near the spool and then travels to the print head. The tube is loosely fixed to the wire harness. At the extruder end there is a cut in the tube and then another smaller piece of PTFE tube goes into the extruder itself. Keeps the filament clear and safe. The PTFE tube is 3mm inner diameter to let it be drawn more freely. The split in the tube at the extruder end also means that retractions just lift the tube there rather than force the filament all the way back to the spool.
I've never noticed filament getting very brittle inside the tube and it's been left in there for weeks at a time occasionally. So either the tube keeps it "fresh" or I just got lucky? Though some of the PLA filament used is coming on 3 years old.
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@phaedrux, just like your experience, I have had filament go bad just where it enters the ptfe tube but never in the tube itself. This was a very weird situation and I have no idea why this happened.
Just to clarify, the spool was less than a year old but has been out of the vac bag for probably a month. The printer had been sitting dormant for maybe two weeks. In the past, two weeks is about the time when things get brittle with this filament but I have NEVER had issues with it going brittle inside the tube but it would frequently fail just before entering the extruder prior to the PTFE tube in my prior Bowden setup.
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Thanks for all the replies guys. It seems that there is no real consensus on what the best method is for routing the filament. Phaedrux, I like the idea of using a fatter tube up to the extruder and then the regular tube into the extruder itself - I might give that a go.
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The larger ID definitely helped reduce friction for filaments that had a rough texture. Only time I've had a filament break inside of the tube was with some stone based filaments that are just naturally brittle. A runout sensor is a must for those.
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@deckingman, thanks for your input. I have actually seen how you have done things. It's a mystery to me how this all works together but it sure is interesting.
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@phaedrux said in Filament routing for direct extruder:
The larger ID definitely helped reduce friction for filaments that had a rough texture. Only time I've had a filament break inside of the tube was with some stone based filaments that are just naturally brittle. A runout sensor is a must for those.
Never experimented with anything exotic but a runout sensor is definitely a requirement no matter what. My printers run unattended and not having a runout sensor usually would result in a loss of hours of printing. I don't understand how people think a runout detector is optional.
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I run filament straight down from the top of the printer to the extruder through the electronics enclosure. No tubes that add friction. The hole through which the filament enters the print chamber is directly above the center of the print bed and I put the electronics high enough above the bed to let the filament feed easily even when the extruder is at the corners of the 300 mm square bed.
I didn't want a tube to guide the filament because of friction it adds which has the potential for causing print artifacts as the extruder tries to pull the filament while extruding and/or disturbances in the motion of the extruder carriage caused by the friction of a filament tube. I mount the spool on a holder with ball bearing rollers that prevent the filament from springing over the flanges of the spool and tying itself into a knot.
What you can't see in the picture is that inside the electronics enclosure there is a cone with a small hole were the filament enters and a large hole (maybe 75 mm dia) where the filament exits the bottom of the electronic enclosure and enters the print chamber.
The top of the print chamber to the entrance of the extruder is about 150 mm. For a 500mm square bed I'd probably bump that up to 250- 300 mm. Making printers taller is usually not nearly as big a problem as making them wider (fitting through doors, etc.).
If I had been smarter about it, I would have made a platform that the spool holder would sit on at the bottom of the electronics enclosure and then cut the top cover to fit around it so that I could remove the top cover while the machine is printing without having to move the spool holder.
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@mrehorstdmd, interesting, thanks for posting.
