filament wound around gear  

RE: filament wound around gear

Good morning Hansjoerg,

as you know, TPU is a flexible material and this makes it more difficult to print with. 

so first issue...    getting it out of the extruder...     
I heat the extruder to a reasonable temperature (say 240C) , whilst it is heating I loosen the Bondtech trap door tension screw and open the door,  then whilst pulling on the filament from above, I select the remove filament option on the LCD menu, and... usually the filament comes out, occasionally you have to do this two or three times. 

when re fitting the tension screw for the bondtech trap door, make sure that you have the absolute MINIMUM tension on the screw / spring.

if the  tension is too high, the TPU tends to wrap around the Bondtech gears instead of following through the extruder channels.

I also find that TPU prints better if you set the retractions to 0mm.  

regards Joan

RE: filament wound around gear

Alos, when loading TPU don’t use the auto-load feature, turn it off. It tries to load way too fast which can lead to what you’re seeing. I had the same (though somewhat less severe) issue when I first tried auto-loading TPU. I was able to untangle it by a combination of snipping, pulling with needle nose tweezers, and slowly turning the extruder motor. 

RE: filament wound around gear

Matches my first experience with flex filament.

That stuff is not stiff enough to force itself down the PTFE tube.

My first print was fine but a little stringy, so I dropped the temp by 5 degrees to 205. Big mistake...

The entire object "printed" inside the extruder. Wrapped around, balled, you have it.

I was sure it would be a full disassembly. Working on that, I moved the printer to the kitchen table for good visibility.

Cut the filament a bit above the extruder. Used a set of dental picks to catch the filament above the gear.

With a lot of struggle, got the filament below the gear. Fortunately - flex is incredibly tough - and stretchy.

I never did break the filament by pulling on it. Once I just had a balled up mess between the Bondtech and the motor, 

I got in with fine needle nose pliers and just started teasing it. Eventually the filament unthreaded itself.

No problem getting it out of the PTFE tube. Then I replaced all the extruder screws I did not need to remove in the first place... 

RE: filament wound around gear

Oh - as Joan said set the retraction to zero. Flex (TPU) does not like retraction... I set up a profile specific to flex for this reason.

RE: filament wound around gear

Also, I’ll refer you to a post I made on my experience printing TPU. 

My Experience Printing TPU

RE: filament wound around gear

Posted by: @mdaneman

Also, I’ll refer you to a post I made on my experience printing TPU. 

My Experience Printing TPU

Should be required reading. Thanks!

RE: filament wound around gear

So here is my entry in this category 🙂

I found a hint that may be useful for some. Once I got most of the filament out with tweezers, small screwdrivers and uber needle nose pliers, (2 hours) there was one piece left right at the back of the gear cavity. No amount of poking or prodding worked it loose. It was stuck under the gear, and if I did an unload the gear tightened up on it.

So I set it to filament Load, and inserted a short piece of filament into the extruder feed hole just enough to trigger the filament sensor (but not go in the gears) - and voila the extrude motor started in the load direction and the filament piece just spit right out.

BTW this was my first print with FLASHFORGE PLA+PLA PRO White. I set it to 5mm retraction as per recommendations (default was 0 in PrusaSlicer) - maybe this caused the issue? 0.1mm layer height at 215/50C. This filament "feels" significantly more stretchy than the Prusa one that came with the printer.

gny

RE: filament wound around gear

@george-y-2

Hi George, 

where did you get the instruction to use 5mm retraction... 

that sort of value may be ok for a bowden feed extruder, but a direct drive extruder like the Prusa mk3S  and mk3S+, don't need that sort of retraction, in fact you may well find 5mm retraction to be excessive and cause blockages and filament twisting in your extruder.
also, is the screw which is marked with a Red arrow, loose? 

RE: filament wound around gear

Thanks for the response and the info. I was thinking the retraction might be the issue. I got the value from the Amazon listing for the PLA I bought  from a user's review that said 5mm worked well for them.

Looking for suggestions - should I go back to default zero mm retraction, or something in between 0 and 5?

https://www.amazon.ca/gp/product/B0833FH3V5/ref=ppx_yo_dt_b_asin_title_o01_s00

Other have mentioned as well that I may have a screw loose ;-), but in this case the screw is tight. In the pic what looks like screw threads under the head just happens to be light reflecting off the printed ridges in the plastic that the screw is holding.

Thanks again

gny

RE: filament wound around gear

@george-y-2

that picture is misleading isn't it! 

I would go with a 0mm retraction for TPU

regards Joan

RE: filament wound around gear

@joantabb

Thanks! Yes I kinda figured 0mm retraction would at least be a starting point. So went back to 0mm today after a cleaning and cold pull - finished a 7 hr print successfully.

Ciao

gny

RE: filament wound around gear

was the print good?
which basic profile did you use?

I use Sainsmart TPU (98A hardness) and I typically use the generic PLA profile, changing the filament temperatures to the Flex temperatures, and setting retraction to 0mm and I get better prints than I do with the default Flexfil and sainsmart profiles...

it is likely that the large retraction suggestion, was based on a printer with a bowden feed extruder, where the extruder drive motor is fastened to the end of the printer and feeds filament into a LONG PTFE Tube, and then into the extruder assembly through the cold end, into the melt zone of the extruder and out of the nozzle. 

The  softer the filament is, the more likely it is to try and bend instead of being pushed towards the extruder, this in effect creates a 'Filament Spring' inside the PTFE tube. and so, to release pressure o the nozzle between layers, the extruder motor needs to pull back enough filament to take the tension out of the filament spring.

On the Prusa direct drive extruder the filament path is much shorter and there is less chance of the spring effect occurring...
so this is a bit of a Heads UP...    be aware, when looking for advice, that different printer styles have different needs... the Prusa with Direct drive, rarely needs more than 0.8mm retraction(I tend to use 0.4mm retraction) except for TPU where I use 0mm retraction. (the Mini and the MMUv1 are both Bowden feed, and Prusa recommend 4mm retractions, I used 2mm retraction on my MMUv1)

Regards  Joan

RE: filament wound around gear

@joantabb

Hi - yes the print was very good. Slight stringing but really hardly noticeable. Four hours into the next print and all looking great. The surface looks really good with this PLA and and a 0.1 layer height. I was thinking of turning down the temp by 5C but didn't yet. Maybe next print.

I totally get ur explain on the retraction settings between the two types of print heads. Pity the manufacturers don't specify/differentiate that in their print settings. And yes - i will pay more attention to the "source"

I've also printed a Sainsmart TPU with very good results , using the Prusa Sainsmart presets with temps to 250/60 C - absolutely no issues.

Also ordered the BigTreeTech filament smart sensor today to see how that might help. I think I will raise a separate discussion on that... re merits of mounting that on the reel end or the (direct drive) extruder end.

Thanks again for your help,

gny

RE: filament wound around gear

Howdy,

I seem to have the same problem.  Trying to figure out how to set retraction to 0.  There seem to be 2 different settings.  Retraction set at the Filament level as well as the printer level.  Should I do both?  Does PrusaSlicer have a setting that one overrides the other.  Any help would be greatly appreciated.

RE: filament wound around gear

@theonepete

Filament setting override printer setting, if there is a value in filament

RE: filament wound around gear

Thank you!