FLEX Filament jammed in PTFE tube because of too much friction in it
 

[Solved] FLEX Filament jammed in PTFE tube because of too much friction in it  

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julian.s10
(@julian-s10)
Eminent Member

I have two PRUSA printers: MK3 and MK3S.

I found a serious issue with new MK3S extruder and FLEX filements, a issue that doesnt't occur in MK3 but only with MK3S. When FLEX filament goes through extruder gears it has some marks with an excess of pressed material and it causes too much friction in PTFE tube. I tried to loosen a screw with spring to the maximum possible distance but extruder gears are so sharp that they still leave recess in fiament and it results with stuck filemant in PTFE tube. I did a quick test with removed PTFE tube and untouched filament. It works perfectly. Filament which goes through extruder gears blocks itself because of too much friction of excess of material created by gears.

I have two gueses what may be done to solve this. Trying to replacing spring from extruder door screw with the weaker one (original seems to be too strong). Secong guess is to file off extruder gear teath so they would use friction instead of biting into filament.

What do you think? 

I am really dissapointed that the upgrade decreased abilities of previous PRUSA printer which can print both PLA and FLEX. I also bought Extruder upgrade for MK3 to MK3S but now I have many doubts if it is really good option.

Has anybody the same problem with new MK3S PRUSA printer?

 

Best Answer by julian.s10:

Installing latest Slicer (>=2.0) and generating gcode from it solved the problem for me 🙂 (crushed PTFE tube was also a problem but the main reason of failed printouts with FLEX filament was a gcode generated from Slicer with improper version of it)

This topic was modified 2 years ago 4 times by julian.s10
Posted : 03/06/2019 11:56 am
Patrick.b liked
julian.s10
(@julian-s10)
Eminent Member

update: the most probable reason of this error is squeezed PTFE tube by extruder casing (near the position of bondtech gears)

Posted : 04/06/2019 9:41 am
Bunny Science
(@bunny-science)
Noble Member

You may do better with an extruder with a corrected filament path like a Butterworth or BNBSX. Prusa R4 aggressively protrudes motor shaft Bondtech into filament path. It is so aggressively positioned that some report their MK3S will drive filament forward WITHOUT the idler door Bondtech giving counterpressure. That isn't a great alignment for flex filaments.

Extruders with corrected filament paths have less aggressive Bondtech positioning.

Posted : 06/06/2019 6:44 am
julian.s10
(@julian-s10)
Eminent Member

One week of tries and still I am not able to print with flex. I print 9 items one by one on the plate and filament jam occurs aearly after finishing one item and starting other one (because of retraction probably). Do you think ordering whole extruder from MK3 will work with MK3S printer?

Posted : 07/06/2019 3:36 pm
terry.k
(@terry-k)
New Member

Julian, I seem to be having the same problem. I'm trying to print Prusa Flex. Flexfill 98a and after a few minutes the filament starts to back up and ceases to feed through the hot end. 

I'm new with the Prusa but I've been successfully printing with PLA. 

Investigating the Slicr filament setting for 98A I see the print volume is by default set to 1.2. which seems strangely high. I shall try reducing this and also normalise my Z height. I've had it at about -500 to get a good stick down with PLA.

 

best regards

Terry

 

Posted : 08/06/2019 3:27 pm
terry.k
(@terry-k)
New Member

So even with the default print volume reduced to 0.9 after about 10 minutes of printing extrusion becomes first restricted by a loop in the filament between the gears and the PTFE tube and eventually stops completely. I'm wondering if the gap between the gears and the PTFE tube is too big. Does anyone have a picture of what it should look like? Here is mine.

?   

Posted : 08/06/2019 4:18 pm
terry.k
(@terry-k)
New Member

I backed off the sprung bolt (which loads the bondtech gear door) as much as I can. I actually put a longer bolt in. But I'm curious. Is it possible to run without the PTFE tube?

Anyway, I renewed the PTFE tube. Initially I got rather better results. I set a long job running (5 hours) and after babysitting the first layer I thought I'd cracked it.

However half way through the part it seems the flow was reduced somehow and the part was spoiled. Some plastic is still coming through but nothing like normal volume. Removing the filament, no loops and seemed to be feeding ok. 

Puzzelled.

 

This post was modified 2 years ago by PJR
Posted : 09/06/2019 7:53 am
julian.s10
(@julian-s10)
Eminent Member

Installing latest Slicer (>=2.0) and generating gcode from it solved the problem for me 🙂 (crushed PTFE tube was also a problem but the main reason of failed printouts with FLEX filament was a gcode generated from Slicer with improper version of it)

This post was modified 2 years ago by julian.s10
Posted : 12/06/2019 4:14 pm
Patrick.b
(@patrick-b-2)
Prominent Member
Posted by: julian.s10

I have two PRUSA printers: MK3 and MK3S.

I found a serious issue with new MK3S extruder and FLEX filements, a issue that doesnt't occur in MK3 but only with MK3S. When FLEX filament goes through extruder gears it has some marks with an excess of pressed material and it causes too much friction in PTFE tube. I tried to loosen a screw with spring to the maximum possible distance but extruder gears are so sharp that they still leave recess in fiament and it results with stuck filemant in PTFE tube. I did a quick test with removed PTFE tube and untouched filament. It works perfectly. Filament which goes through extruder gears blocks itself because of too much friction of excess of material created by gears.

I have two gueses what may be done to solve this. Trying to replacing spring from extruder door screw with the weaker one (original seems to be too strong). Secong guess is to file off extruder gear teath so they would use friction instead of biting into filament.

What do you think? 

I am really dissapointed that the upgrade decreased abilities of previous PRUSA printer which can print both PLA and FLEX. I also bought Extruder upgrade for MK3 to MK3S but now I have many doubts if it is really good option.

Has anybody the same problem with new MK3S PRUSA printer?

 

Yes exacty same idea, i just upgrade to S and i was so happy and now so disappointed, i don't understand anymore..i had perfect printing , with all filament , even with flex no jammed, no stuck in idler , except if i set very high retraction in slicer , to avoid stringing , otherwise flex , pla, abs , petg all very good and not 1 time filament jammed, i open all, change the nozzle with original, correct the tube the head cut a very little..., print the square test , print another spool , with few stringing in PLA !! but with different gcode i have lot of stringing and jammed, only when the extruder have to moove a lot from 1 side to other and doing lot of retraction (no correction of prusa profil .8 ..and each time after 1hr about , click click click.......voila ..i really don't get it ..i check the idler is ok the axe is strong...i moove the screw tight not too tight..same same.. 😪 😪 😪 😡 😡 

Posted : 18/06/2019 9:28 pm
tim.s16
(@tim-s16)
New Member

I have a similar issue. The filament gets loaded and extruded but the extruded material gets less and less. It also seems to me as if the extruder is moving much to slow.

I used PrusaSlicer and the latest firmware 3.7.1.

Posted : 18/06/2019 10:10 pm
Patrick.b
(@patrick-b-2)
Prominent Member

it might be come from left fan from my side , will back if this is issue !

Posted : 19/06/2019 8:43 am
julian.s10
(@julian-s10)
Eminent Member

After one more week of tests I found that the main reason of FLEX filament jamming in the extruder is dust which accumulates in the PTFE tube and which creates a lot of riction. After removing tube and cleaning it with some stiff filament (by hand) the printer prints with FLEX without any problem (of course you have to rememeber about generating gcode from the newest slicer). Other problem I noticed is that the new hotend tends to leak a lot of filament during non printing moves. Do anybody knows how to solve this problem? What's the name of that phenomenon?

Posted : 19/06/2019 10:24 am
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