How do I stop TPU coming out the side of the extruder?  

Re: How do I stop TPU coming out the side of the extruder?

Hi Kevin,
are you using the Flex Profile in Slic3r?
is your extruder ptfe liner visible in the bondtech inspection chamber, under the hobbed gears? the closer it is to the gears, the better it will constrain the flexible filament, if it's not visible, check your extruder installation, if it's visible but there is a gap, consider replacing the ptfe with a slightly longer one, to reduce the gap!

one at a time,
try reducing the screw tension on your extruder bondtech, filament clamp,
and
try printing more slowly
try raising the extruder temperature

regards Joan

Re: How do I stop TPU coming out the side of the extruder?

How do I stop TPU coming out the side of the extruder?

What slicer are you using? If you're using Slic3r, try setting Filament Settings->Advanced->Max. Volumetric Speed to something low (e.g. I use 1.5 for NGEN Flex versus 15 for PLA or 8 for PETG). It will be slow... very very slow... but it may print more reliably. You can try increasing it gradually if it works at a slower volume.

Re: How do I stop TPU coming out the side of the extruder?

The gap from the bondtech gears to the PTFE tube must be minimal. I found this upgrade on Thingiverse, https://www.thingiverse.com/thing:2867249 to help closing the gap. Have not tried it yet but plan to... 😛

The bondtech gears must be loose to not deform the filament. If to tight the filament tends to come out the sides.

Re: How do I stop TPU coming out the side of the extruder?

Thanks all.
I bought my MK3 assembled so have not yet got my hands dirty tweaking the hardware/setup yet.
Time to start... 😁

Re: How do I stop TPU coming out the side of the extruder?

The gap from the bondtech gears to the PTFE tube must be minimal. I found this upgrade on Thingiverse, https://www.thingiverse.com/thing:2867249 to help closing the gap. Have not tried it yet but plan to... 😛

The bondtech gears must be loose to not deform the filament. If to tight the filament tends to come out the sides.

I printed that addon. The part came out BEAUTIFULLY, but I found that it rubbed the bottom side of my extruder gear, which caused skipping. My parts all came out extremely underextruded until I removed it. I haven't taken the time to rework the part yet. Maybe there is a way to raise the gear a bit instead?

Re: How do I stop TPU coming out the side of the extruder?

I will give them a try. The MK2 prints TPU without any problems.....

Re: How do I stop TPU coming out the side of the extruder?

Skelestruder upgrade is designed to eat TPU for lunch (in a good way). No escape path by design.

Re: How do I stop TPU coming out the side of the extruder?

My advice would be to buy a printer that the manufacturer cares about.

Re: How do I stop TPU coming out the side of the extruder?

How do I stop TPU coming out the side of the extruder?
Can you provide more detail on how you're printing? What slicer, what settings?

I had a similar experience when I 1st tried Colorfabb NGEN Flex (95 hardness IIRC). I set it aside until I figured more out. I recently purchased a roll of Inland TPE (85 hardness) which is even spongier. Using Slic3r, I tried setting the filament Max volumetric speed to 1 and it printed well on my 1st try. The 5 in the Prusa NGEN Flex profile was too fast, but I found I could get reliable prints at up to 2.5. I went back and used up the rest of my 200g roll of NGEN Flex without a single jam.

Unfortunately, Slic3r seems to be the only slicer with this option. You can approximate something similar with speed settings, but this setting takes into account nozzle bore, line width, layer height, speed and acceleration to ensure the extruder isn't overwhelmed by any one factor. I've been having the most luck adjusting this setting with new filament before trying any other tweaks. So far, I've had success with Colorfabb NGEN Flex, Inland TPE, Colorfabb XT Carbon Fiber (CF20), eSun woodfill, 3D-Fuel coffee fill, various copper and steel fills.

Fortunately for all of us, Prusa is putting a lot of work into improving not only the hardware, but the supporting software as well. Slic3r keeps getting better & better. I'm not aware of another firm that has dedicated so many resources towards improving the printing experience.

Re: How do I stop TPU coming out the side of the extruder?

My advice would be to buy a printer that the manufacturer cares about.

Re: How do I stop TPU coming out the side of the extruder?

Is there some way they can extend the tube so that they meet at the Bondtech pulley in the Idler Assembly? My thought would be some kind of half tubing above and below the Bondtech pulley inside the back half of the Extruder-body. The front half of the two tubes, maybe 2mm inside diameter could be attached to the Extruder-idler door.
When the door is closed the two halves form a restraining tubes around the open space where TPU can bulge out and cause this problem. The two halves don't even have to touch, there could be a small gap as long as it fills in the pathway to keep the TPU from folding over.

Is this design possible or is it easier just to design an entirely new Extruder Assembly?

Re: How do I stop TPU coming out the side of the extruder?

Is there some way they can extend the tube so that they meet at the Bondtech pulley in the Idler Assembly? My thought would be some kind of half tubing above and below the Bondtech pulley inside the back half of the Extruder-body. The front half of the two tubes, maybe 2mm inside diameter could be attached to the Extruder-idler door.
When the door is closed the two halves form a restraining tubes around the open space where TPU can bulge out and cause this problem. The two halves don't even have to touch, there could be a small gap as long as it fills in the pathway to keep the TPU from folding over.

Is this design possible or is it easier just to design an entirely new Extruder Assembly?

Skelestruder removes all gaps. See v for concept and for action

Re: How do I stop TPU coming out the side of the extruder?

Skelestruder removes all gaps. See v for concept and for action

😯 I didn't think I'd get pumped watching a video about a printer, but you've done it. I may need to build one of these monstrosities!

Re: How do I stop TPU coming out the side of the extruder?

Skelestruder removes all gaps. See v for concept and for action
Impressive!

Why does the filament package say "Ninaflex" though?

Do be careful of the YouTube music copyright enforcement bots!

Re: How do I stop TPU coming out the side of the extruder?

Skelestruder removes all gaps. See v for concept and for action
Impressive!

Why does the filament package say "Ninaflex" though?

Funny, I didn’t notice. It’s from a print shop that sells samples from stock and print their own labels. Just a typo. It came in that ziplock.

Do be careful of the YouTube music copyright enforcement bots!

Yeah, I was wondering about that. Not the full songs, fingers crossed.

Re: How do I stop TPU coming out the side of the extruder?

Damn your extruder is tempting...

Re: How do I stop TPU coming out the side of the extruder?

Hi Kevin,
are you using the Flex Profile in Slic3r?
is your extruder ptfe liner visible in the bondtech inspection chamber, under the hobbed gears? the closer it is to the gears, the better it will constrain the flexible filament, if it's not visible, check your extruder installation, if it's visible but there is a gap, consider replacing the ptfe with a slightly longer one, to reduce the gap!

one at a time,
try reducing the screw tension on your extruder bondtech, filament clamp,
and
try printing more slowly
try raising the extruder temperature

regards Joan

Joan, I wonder why you suggest reducing the screw tension on the Bondtech clamp? In spite of all that I've done, I'm still having difficulty printing TPU. The filament always "escapes" on the idler side, and it occurred to me that maybe the filament is actually pushing against spring tension and literally moving the idler away from the drive gear. So my next experiment will be to try increasing the spring tension.

By the way, the part that I'm trying to print has a rather large "pancake" and the print will often fail near the middle of the pancake. That's where the air flow from the print fan has the greatest focus on the nozzle itself because the air can't flow down and away from the nozzle. This means that the tip of the nozzle is cooler than the hot zone where the thermistor is located. So yesterday I tried turning off the print fan completely and got four layers of the pancake printed without a failure. I don't really see why the print fan is needed for flexible filament, unless you are doing some very fine work with very short-duration layers.

Another thing is adjustment of the length of the PTFE tube in the extruder body. Apparently you can assemble the extruder and think that you have the PTFE tube just about touching the Bondtechs, but the flexible filament will find a way to push down on it. So the next time I install a new tube (tomorrow?) I'm going to push down on it very firmly by hand before I decide whether it's the right length and installed correctly. I've made a jig so I can cut the tube with two 45 degree slopes so the top of the tube has "ears" that constrain the filament from going astray along the axis of the Bondtechs.

And yet another thing I'm going to do: I now have plenty of PTFE tubing so I'm going to do a "reverse bowden" from my dry bag all the way to the top of the extruder to keep the filament really dry.

regards, Jay

Re: How do I stop TPU coming out the side of the extruder?

Joan, I wonder why you suggest reducing the screw tension on the Bondtech clamp? In spite of all that I've done, I'm still having difficulty printing TPU. The filament always "escapes" on the idler side, and it occurred to me that maybe the filament is actually pushing against spring tension and literally moving the idler away from the drive gear. So my next experiment will be to try increasing the spring tension.
I think the idea is that you want to grip the filament without deforming it. The flexible filament deforms very easily, so minimizing the tension reduces the deformation.

Another thing is adjustment of the length of the PTFE tube in the extruder body. Apparently you can assemble the extruder and think that you have the PTFE tube just about touching the Bondtechs, but the flexible filament will find a way to push down on it. So the next time I install a new tube (tomorrow?) I'm going to push down on it very firmly by hand before I decide whether it's the right length and installed correctly. I've made a jig so I can cut the tube with two 45 degree slopes so the top of the tube has "ears" that constrain the filament from going astray along the axis of the Bondtechs.

And yet another thing I'm going to do: I now have plenty of PTFE tubing so I'm going to do a "reverse bowden" from my dry bag all the way to the top of the extruder to keep the filament really dry.

If you haven't done it yet, I strongly suggest that you upgrade to the R3 extruder parts. The changes in the R3 version were specifically intended to reduce problems with flexible filaments, and it worked for me. R3 gives you a much more constrained filament path below the bondtech gears. Flexible filament stays in place because it simply has no place else to go.

Re: How do I stop TPU coming out the side of the extruder?

Hi Jay,

excess tension on the extruder screws, tends to distort the TPU and cause it to pop out between the bondtech and the PTFE...

your mileage may vary

reverse bowden sounds like it will keep your filament dry!

I have printed R3 parts for the extruder. but not fitted them why modify a working printer...
I am expecting my MMU2, soon, so I will do the R3 extruder parts then.
the R3 parts are supposed to work better with TPU.

I only have cooling problems where the layer time is very short... some of my parts have little peaks at the top, which require full cooling and reduced speed... you can set your fan to come on, at higher layers, and less speed, in Slic3r or another slicer

good luck, Joan