Unresolved Flex filament, won't feed.

Robo R1 E3dv6 hot end.. Ninjaflex-TPU , black.

Prints start out OK but pretty soon the filament, which is pretty flexy, stops feeding through to the print head as if jammed and starts wrapping around the outside of the hobbed bolt.

This happens if I keep the print head at temperature and just extrude filament,say 100mm or even less.
if I unwrap it and push it down the tube,it will flow out the nozzle. Tried up to 10 degrees hotter, no change.

Not sure if the issue is the filament getting stuck in the tube/nozzle, catching on the edge of the tube, or, this is just not gonna work due to the design of the drive mechanism

This is my second attempt to work with flex filament, had the same problem last time, now that I think about it.

Any one printed with NinjaFlex -TPU successfully on Robo?

 

I recall converting a similar printer and part of the installation was to miter/chamfer the short piece of PTFE tubing. You may wish to check the exit path of the hobbed bolt to ensure that the tube hasn't twisted. Also I've considered creating the chamfers a bit higher than the opening in the carriage, to minimize the type of trouble you are experiencing.

 

I think I tried that and the filament still found a way to sqjueeze out. I got a bit frustrated trying to chamfer that tubing, so should try again. Thinking I might try shaping it differently this time.

Not sure I get the "exit path of the hobbed bolt" thing, but will check the alignment again and PTFE tube length and shape.

 

I do find a few things.

The PTFE tube is square cut and end 3mm-4mm below the contact "patch" of the roller.

The roller was a bit oft to one side of the "apex" of the hobbed bolt "teeth" Seems the washers on either side of the bolt are of slightly different thickness, and swapping them resolved that.

There is (a lot?) of looseness in the pressure roller "swing arm" where the long thin bolt goes through the carriage perhaps allowing it to shift around as it rotates while filament feeds.

That last bit I recall now I attempted to resolve some time back but that "quick fix" has proven inadequate. A more permanent fix is in order. Perhaps a thicker bolt and a bit of careful machining might be enough.

Any suggestions, known fix?

 

I'll try to find those threads.

I did slow down the print speed to 30mm/sec max, but did not specifically slow the feed rate, which I believe you mean to be the filament feed rate, which I thought was computed by factoring in nozzle size, speed, etc. But will look for a specific setting.

Mean time I made a few small alterations, adjusting the hobbed bolt so the "apex" of the arc is aligned more closely to the PTFE tube, making a new PTFE tube that is cut at an angle to just clear the teeth on the bolt and the pressure roller. That alone may help as the filament always squeezed out in the same direction, consistent with the misaligment of the hobbed bolt.

A plus is this spurred me to work on the idle Big Box again, getting it "almost fully commissioned" but then finding Matter Control cannot talk to it properly. Again. The odd thing, to me, is Arduino has no trouble at all finding it and uploading FW.

Anyway, manually using the BB and looking at changes I needed to make to the firmware, discovered some changes I thought to make on the Robo, namely, quieting the "chirp" from the LCD button and reversing the action of the direction, to make CW move "+" and CCW move "-"; This led me to the discovery I can no longer compile the Robo FW.

Sigh.

 

Oh, I'm sure it can be. That's the thing, I compiled the currently installed firmware on this very same PC and uploaded it, some time ago. Oh well, the search must go on, but that can wait for my filament issues. One must remain flexible after all. I'll get my coat.

 

I just discovered a little "hitch in the gitalong" of a bit of hard non flex filament I inserted down the PTFE tube, as a final test before attempting to print flex.

In other words, it inserts freely until it "catches" a good ways in and requires extra force to "snap out of it" and bottom out about 9mm further down the hole. Seems I have a problem at one of the mechanical transitions along the filament path?

 

Before I go down the path of tearing it down, the filament does extrude manually and at the start of prints. I tend to think, perhaps wrongly, that at that point, the filament is "liquid" and should not be affected.

Maybe first try changing the filament feed (ratio ?) to slow feed rate?