[Closed] MK3 and flexible filament ?  

Re: MK3 and flexible filament ?

GREAT! Thank you! That's the most comprehensive settings post I have ever seen!
Highliy appreciated - I have a roll of NinjaFlex wand want to try it soon...

Re: MK3 and flexible filament ?

I have printed NinjaFlex, but I had to slow way down - 10 mm/s! 20 mm/s generated back-pressure, followed by the filament coming out the side of the extruder. The issue isn't the BondTech gears - they are great - I think it's that the filament path isn't fully constrained around the gears. Well, and of course, that NinjaFlex is absurdly soft.

Gotta be something that can be done. Perhaps a better formed PTFE tube up to the gears. Will try something softer tomorrow. My print came out great, albeit a little string. Changed k to 15 and disabled retraction. So far half way done and it looks clean as can be. So perhaps their is hope. I am happy so far for my first two attempts, and in all fairness I was no expert on FF before.

I agree - I previously printed NinjaFlex with a Makerbot Replicator extruder, with a redesigned extruder such that the filament path was fully constrained before and after the gears. https://www.thingiverse.com/thing:169086 . Of course, I’d really rather print NinjaFlex on the Prusa than an ancient wooden Replicator. I wonder if it’d be possible to add more constrained paths to the Prusa extruder. I’ve seen some designs that used PTFE tubing before and after the gears, too.

Re: MK3 and flexible filament ?

Do you guys have any retraction?

There has to be 0 retraction when printing with flex as Ninjaflex and Tpu...

Thats my experience anyway....Try that if you don't already are....

Re: MK3 and flexible filament ?

Hey guys,

well 0 retract? Didn't test that yet.
I was able to print black TPU with 90-94A (from dasfilament.de). For small objects (like marvin) I could print with about 35 to 40 mm/s, but for larger prints with infill, that was not possible at all. The filament just bent around the gears. I was however able to print with 25mm/s without much issues.
Printbed: 45°C (with glue stick layer!)
Nozzle: 230°C
Fan: 100% for layer 2+
Perimeter/Infill/...: 25mm/s <--- I just saw, that I used manual slowdown in addtion, so it was in fact ~17mm/s, not 25mm/s
Retract: 4mm/s
Retract speed: 35mm/s
Deretraction speed: 30mm/s
Travel: 120mm/s

(I was not doing extensive testing, but that was what I ended up after 5 failed attemps, where it would print gread for the first moments and then tangle up the extruder gears quite heavily)

Re: MK3 and flexible filament ?

I tested 2 filaments over the weekend, a semiflex and NinjaFlex.
Used Devdoc's settings.

Semiflex printed the Octopus very well, with slight stringing, but that material really is only semi-flex. It bends, but is quite hard and does not strech at all. Should be good for some phone cover, but it's so hard it would definitely need some fill-in.

NinjaFlex was quite challenging to get printing - it kept coming out of the extruder on either side.
Managed to load it and print an octopus at 50% speed setting (from same Gcode as the semiflex).
Printed OK but the stringing was really bad. I reallized that retraction was still on.

Any recommendations?

Re: MK3 and flexible filament ?

Just been reading this thread, I’m still waiting for my mk3, something I’ve always found hard to print was TPU ninjaflex. Some critical things were speed at 25 mms or slower, and very little tension on the extruder only really enough to grip it, increasing extrusion multiplayer up. And no retraction at all!

Also stringing is a pain, but use coast and don’t cross permitter to avoid most of it.

Hopefully that might help someone 🙂

Re: MK3 and flexible filament ?

Just had similar experience. Duplicated settings as best I could, glue stick and slow movement and 230, and Ninjaflex out the side of the extruder. Tried loosening off the extruder screws; same result. Waiting for tips and suggestions.

Thanks!

Eric

Re: MK3 and flexible filament ?

Is there any gap between the bottom of the bond Tech gears and the entry into the hot end?

Re: MK3 and flexible filament ?

Just had similar experience. Duplicated settings as best I could, glue stick and slow movement and 230, and Ninjaflex out the side of the extruder. Tried loosening off the extruder screws; same result. Waiting for tips and suggestions.

Thanks!

Eric

I had the same issues, and had to try maybe 5 times until I successfully loaded and extruded without a filament loop coming out the side.
I think in the end I used "move axis"-"Extruder" to slowly feed the filament, and I reduced the printing speed to 50% on top of the settings posted before. That worked for me.

@jonathon:
I use Slic3r for slicing - is there a setting for "not cross perimeters" and "coast"? I can't remember seeing them.

Re: MK3 and flexible filament ?

I don’t think coast is in the prusa version, but definitely avoid crossing permitter is. I hop between S3D and slic3r. Coast is definitely a good thing for flex because it’s so runny! I’m sure lin advace would help too but I haven’t figured the correct K factor for TPU yet, I would think it’s a pretty high valve

Re: MK3 and flexible filament ?

I have had some success! Managed to print a very stringy octopus in 85A Ninjaflex.

In the grand tradition of hacking, I changed many things at once:

1. Increase nozzle temp to 235.
2. Switch to stealth mode
3. Adjust live Z from around -0.780 to -0.5

Can I do the equivalent of live Z adjust in Slic3r with the Z-offset parameter in the Printer Settings? So the printer knows it should be -0.780, so I add a +0.280 and then I'm at -0.5 if I use that printer profile?

Re: MK3 and flexible filament ?

1. Increase nozzle temp to 235.
2. Switch to stealth mode
3. Adjust live Z from around -0.780 to -0.5

In understand the logic behind increasing the temperature (= reduce backpressure to avoid filament coming out the side)
But what was the reason for stealth mode?
Backing off the life Z makes sense - bed ahesion is really not an issue.

Here's a photo of the SemiFlex and NinjaFlex (orange) octopus.
Semiflex was easy, kind of flexible but not "elastic"
Ninjaflex not easy to print, nice soft and squishy, and very stringy...

Re: MK3 and flexible filament ?

To go back to the bondtech gears, I was surprised a few days ago to have some ColorFabb HT ( it's not a flexible; the filament itself is quite rigid) escape out the side of the extruder while loading. It wasn't the buckling hernia of a flexible filament, rather the end just started feeding out the side. I tried it again after re-cutting the filament, and it loaded correctly.

I don't remember what the filament path looked like during assembly -- is the PTFE tube chamfered? I wonder if it's just easier to 'miss' the hot-end tube than on the MK2S, and the gears just shove the filament wherever it'll go. (Or I didn't get the gears properly lined up.)

Re: MK3 and flexible filament ?

I was reading this thread earlier today and decided when I got back from work to try printing some TPU. i knocked up a simple 50mm diameter 5mm high ring and sliced in Slic3r using the same settings I had for my Mk2 and printed it.

First two goes failed with a loud beeping and MAXTEMP. On checking the Slic3r settings I had managed to set the other layers temperature to 1500 degrees! Explains the MAXTEMP!

Having set the temperatures a little more sensibly i tried again and it worked fine with a very small amount of stringing. I will try a different print later in the week.

I used a first layer hot end temperature of 250, subsequent layers 230, bed temperature was 80 and I used talcum powder as an adhesion modifier.

Here is a picture:

Z

Re: MK3 and flexible filament ?

Looking good! What TPU is this?
Hard or soft flexible material?

Re: MK3 and flexible filament ?

It is a flexible TPU from Rigid Ink in the UK

Z

Re: MK3 and flexible filament ?

I took your inspiration and pushed my openscad skill to the limit and created a ring 😀 Used Sain SMART TPU I had found on amazon

I used the Slic3r included profile for semiflex/flexfill as a starting point and then cranked the nozzle to 230 first and all layers and the bed to 65 first and all also.

Loosened the extruder idler screws per the instructions in the the 3d printing guide (wasn't sure how much to tighten them during assembly or loosen them now, but I just made a guess both times).

Printed very nicely, not stringy at all.

Will try something a bit more challenging next

Re: MK3 and flexible filament ?

I'm currently consulting/helping someone doing shoe inlays, flex material is a must in this case.

For me this means a lot of frustration, but I might have found a way to improve printing with Flex materials.

Observations:
So after several tries with different settings, slicers and materials (5 different ones), none really seem to work. The issue is, that the material ALWAYS gets tangled below the Bondtech (and before the extruder). If noticed in time, a print pause with a hearty filament pull and reload helped to recover from some messed up filament. Even with low print speeds, and manual change of print speeds reduced to 50 on the printer the filament was running any other way than through the hotend.

Extruder disassembly:
Today I took the time to disassemble the extruder (if anyone from Prusa is reading, you should really work on easing that process, far to many screws and cables in the way!!!).
So there are two PTFE tubes in the extruder, one in the top part leading to the Bondtech (no issue here). The second one is in the hotend and ends in my case a couple of millimeters below the bondtech. So there is a gap in which the flex materials love to escape!
In short the PTFE tube is a bit to short @PRUSA - please have a look at this!

What I did:
From a bowden system I cut a longer piece of PTFE tube and replaced the original one. I reassembled the hotend partly and then cut the PTFE tube. The gap is closed a bit more now.

Result:
Voila, at print speed of 100 with small retraction enabled I could print for several hours before the first filament escape (which I noticed in time and could fix with a good pull and reload). So I'm much more happy than before, but still I had one escape.

Next step:
I'll dissassemble the hotend again tomorrow and will replace the PTFE tube again. This time I'll mark the length prior cutting and I'll do a V-shape cut going up all the way to the gears. This will close even more the gap and hopefully prevent and future filament escape. I guess it's a simple fix with a great amount of work around the hotend but with an even greater chance for success!

final thoughts/conclusions:
The bondtech gears are excellent, great choice Prusa, But the path between gears and hotend has a far to big gap to be used with flexibles. Please reconsider to improve the PTFE tube length and cut (v-shape) or do something else. It can easily be improved and I hope to see you doing so!

Re: MK3 and flexible filament ?

I absolutely agree with that recommendation. having a "closed" filament path is essential for printing any flexible filament.
i'm still waiting for my MK3, but on my DIY Kossel i can print TPU with almost standard speeds and retract length without any problems. it is one of my favorite materials as i print lots of parts for quadcopters where this material has the features i need there.

Rainer

Re: MK3 and flexible filament ?

Tim.k5 good work. I'd be willing to go through the trouble of disassembling the hot end if I knew what length and size PTFE tube to get for replacement. If you figure it out please share.

On another note, anyone have experience printing Cheetah filament? Are the settings for semiflex best for this type? I'm trying to dial in my MK3 for flexible use with cheetah first then full flexible filament.