MK3S (!!!) ptfe jamfor the second time!  

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paul.a3
(@paul-a3)
Active Member

I’ve had a few of these before with PLA but today got a particularly nasty one printing ASA in my lack enclosure. Picture would basically be the same as the others, enlarged head of the broken off part of the filament impacted in the PTFE so you can’t remove it.

Was printing ASA on a MK3S with the included PrusaSlicer profile at 265 on the nozzle. Temperature in the enclosure was probably about 30, ambient around that was much lower. Didn’t check the extruder stepper temp but was definitely too hot to touch.

What are people doing when they encounter this to get the filament out? I’ve been lucky in the past and been able to force it through or get some purchase on it with some pliers to remove it but not this time. Obviously can disassemble, heat and remove but that is a major pita.

I’d love to print ASA outside the enclosure but it just isn’t going to happen without things warping off the plate. For PLA I just leave the doors open and it is usually fine, but for ASA, Nylon etc I pretty much need the enclosure.

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Posted : 11/08/2019 10:06 am
paul.a3
(@paul-a3)
Active Member

In the meantime, have cleared it using a probably inadvisable technique. I had some 1.2mm wire around so I heated up the very tip with a hot air gun to the point where it would soften the ASA. I then inserted this (quickly) into the hotend and down to the filament end where it melted it enough to have the filament encase the wire when it cooled. I was then able to slowly pull out the wire and filament together enough to cut the deformed tip and then unload normally.

I say inadvisable since obviously that hot tip will also melt anything else it touches, particularly when hot enough to melt ASA. Moving fast however at least ensured no significant contact with the rest of the extruder. In any case, I wasn't in the mood to disassemble the extruder today.

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Posted : 11/08/2019 10:43 am
Tim
(@tim-m30)
Illustrious Member

With a jam where the filament is not accessible, heating the hot end to 280c and pushing the filament through with a wire will work.  If the nozzle is clogged, and you can't push filament, remove the nozzle, and then there is nothing stopping you from pushing the filament down and out.

 

It is always wise to get more than one opinion......
Posted : 11/08/2019 8:19 pm
paul.a3
(@paul-a3)
Active Member
Posted by: Tim

With a jam where the filament is not accessible, heating the hot end to 280c and pushing the filament through with a wire will work.  If the nozzle is clogged, and you can't push filament, remove the nozzle, and then there is nothing stopping you from pushing the filament down and out.

Usually the wire push through is my go to technique, at least with PLA (I now keep one beside the printer for this), however in this case it wasn't enough. Are you relying on creep from the extra heat to make its way up to the top of the PTFE tube when doing this? Or was the assumption that if the filament could not be pushed through it was a nozzle jam?

In my case the issue was the very end of the filament had been deformed (swelled) to the point that it could not re-enter the PTFE, so pushing through with the (cold) wire was not sufficient (in this case the nozzle was not clogged, it was the physical shape of the filament that prevented it being pushed). I can imagine with PLA things get hot enough to soften the tip but not with ASA.

The issue is how did the filament become soft enough to deform below the extruder gears in the first place. Usually when it's just ground up from a jam further down the remaining top is not swollen and often even accessible with pliers. Many seem to blame this on heat creep from the stepper, but there also seem to be a lot of people without any issues.  It does seem to disproportionately affect people using enclosures as well.

I'll probably do some cold pulls now that it is cleared in any case to make sure there are not still issues further down. Just glad I didn't need to tear it down on this occasion.

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Posted : 11/08/2019 11:45 pm
Tim
(@tim-m30)
Illustrious Member

The PTFE is not usually where the filament is jammed.  The jam happens a lot lower, and the extruder gears merely chew through the filament until it breaks off.

The actual jam is the heat break step. 

In some cases, heating the nozzle and forcing filament through with a big stick will clear the jam, but just as often people need to pull the nozzle force things through; and there are times when the heat break needs to be removed to allow the filament to be removed.

 

The Prusa design has a small hole on the top (1.85 mm PTFE), a small hole on the bottom (2.0 mm nozzle), and a wide hole in the middle (2.2 mm heat break).   If filament expands in the heat break to 2.2 mm, it becomes jammed and can't move up or down the feed path.

People call it a PTFE jam, but the PTFE is not the issue.  It is the heat break.  The rare case where it isn't the heat break is when printing inside enclosures the motor and gears get hoot enough to melt PLA ABOVE the PTFE.

And unload after a jam that exhibits a stub like these needs to consider changing the heat break.

This is poly-carbonate: 

This post was modified 1 year ago 2 times by Tim
It is always wise to get more than one opinion......
Posted : 12/08/2019 6:50 am
paul.a3
(@paul-a3)
Active Member
Posted by: Tim

People call it a PTFE jam, but the PTFE is not the issue.  It is the heat break.  The rare case where it isn't the heat break is when printing inside enclosures the motor and gears get hoot enough to melt PLA ABOVE the PTFE.

Above the PTFE was the issue in my case, though I am quite surprised given I was using ASA at the time and not PLA. Basically the tip was pushed into the top of the PTFE where it has the small funnel profile, I can only assume the filament was soft enough to deform since it took on a golf tee like shape matching the entry to the PTFE. This then cooled and solidified so the tip could not enter. It sounds like this is a more unusual case and not necessarily the same as the original posters.

Enclosure is feeling like it is creating more problems than it solves at this stage. I switched to my MK2.5S, no enclosure and got the print out without trouble. Only difference was there were stress marks from where the ASA wanted to warp off the powder coated PEI but couldn't, where as in the enclosure these were absent. With a big enough object I suspect I'd still have problem outside the enclosure but the powder coated sheet does seem to hold on a lot stronger. In any case, that is OT.

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Posted : 12/08/2019 7:01 am
volker
(@volker)
New Member

Hi,

I am experiencing the same Problem. Some times a print  will work fine, but often enough the filament  jams and I have a hard time clearing the ptfe  tube. This is very frustrating.

Is there any solution how to avoid this problem? Btw, My cheap Ender works  without larger problems in comparison.  

I am printing  with the first silver pla coming with the kit and I am printing with suggested speed and temperature.

 

Posted : 18/08/2019 1:59 pm
guy.k2
(@guy-k2)
Noble Member

It also doesn't help that the newer extruder no longer has an air vent hole on the left side the extruder. Heat has to have a means of escape or temperature will rise.

You can get away with it on a geared extruder. Those don't directly conduct motor heat into the chamber, but on direct drive it's an extra factor.

If I was stuck with a stock extruder, I'd add heat sinking or a cooling fan to the extruder motor. Once could strap on an external gearbox, but if you are doing that, you may as well upgrade to a different extruder and also fix the filament path.

Posted : 18/08/2019 9:08 pm
Tim
(@tim-m30)
Illustrious Member
Posted by: eyals

Seems like it’s a major problem when using PLA on MK3S with the current extruder design.

It seems like a new issue with MK3S that did not appear in MK3...  I hope we will get an official response/solution from prusa....

 

There are a lot of us MK3 owners who do not have this issue; we simply don't print inside enclosures and our room temperatures are air conditioned.  My motor runs hot - 58c) but has never melted the filament nor caused a jam.  I think the majority of users don't have any issues with this. So I don't expect any solution from Prusa.  I do expect the melting parts issue to be addressed, but for room temps, not for 60c enclosure conditions.

 

It is always wise to get more than one opinion......
Posted : 19/08/2019 2:02 am
paul.a3
(@paul-a3)
Active Member
Posted by: Tim

but for room temps, not for 60c enclosure conditions.

Are people really running their enclosures this hot? I barely peak at 40c inside mine (Prusa LACK).

Given Prusa recommend themselves, printing in an enclosure for certain types of filaments, including their newly released Prusament ASA, one would not unreasonably expect that they would offer some method of mitigating enclosure related issues should it turn out that is what these are. At least in the form of some advice if not printer modifications.

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Posted : 19/08/2019 10:01 am
The Trek Nerd
(@thetipgiver)
Eminent Member

Yes.  There is another thread all about this.  The conclusion is what was previous stated in this thread:  Buy and "install the stock e3d heatbreak instead of the prusa one." 

I did this and haven't had a single jam since. 

Posted : 19/08/2019 5:12 pm
volker
(@volker)
New Member

Did you change anything in the slic3r settings after installing the new Heatbreak? 

Posted : 19/08/2019 5:32 pm
The Trek Nerd
(@thetipgiver)
Eminent Member

Nope.

Posted : 19/08/2019 6:01 pm
Tim
(@tim-m30)
Illustrious Member
Posted by: The Trek Nerd

Yes.  There is another thread all about this.  The conclusion is what was previous stated in this thread:  Buy and "install the stock e3d heatbreak instead of the prusa one." 

I did this and haven't had a single jam since. 

This isn't entirely the whole truth.

There are two common modes of jams.  One below the Bondtech gears, and one above the Bondtech gears.

The jams that happen below the Bondtech gears, in open and enclosed spaces, are often caused by high retraction gcodes pumping melt upwards in the heat break, where it cools and jams because of the 2.2 mm to 2.0 mm step in the Prusa version.  This is cured by replacing the Prusa version with a stock version heat break - a suitable option for non-MMU owners, and many MMU owners have also done this without consequence.

The jams that occur ABOVE the Bondtech gears, where filament piles up in or just above the PTFE (also called a PTFE jam), are related to the motor and enclosure temperatures climbing above the filament glass temperature.

The motor runs about 35c over ambient.  In normal room temps, 25c, the motor reaches 60c.  If there isn't a lot of circulation in the room, the motor heats the shaft and Bondtech gears, where it impacts filament.

When running inside an enclosure with a 40c ambient, the motor heat raises it's temp to 75c.  This heat at the gears is enough to soften and even melt PLA. So as the filament goes through the gears, it softens, and can no longer make the slight bend into the PTFE, and piles up into a mess.

So TWO issues, each with it's own solution.

Inside an enclosure you NEED the fan modification if you are going to print PLA (or leave the enclosure doors OPEN for PLA.

This post was modified 1 year ago by Tim
It is always wise to get more than one opinion......
Posted : 19/08/2019 7:44 pm
The Trek Nerd
(@thetipgiver)
Eminent Member

Agreed that there may be one cause or many. In my case it seemed to be only one. 

Also make sure the filament isn’t getting wrapped around itself on the supply spool. Even just one strand is enough to cause similar symptoms. 

Posted : 19/08/2019 8:31 pm
da4throux
(@da4throux)
Active Member

Personally, I only had to change the PTFE tube and now it's been working fine for months.

Also I leave my enclosure open all the time, it's more a dust protection when I'm not using the printer.

Posted : 21/08/2019 7:10 pm
scottsh
(@scottsh)
Active Member

I had the problem of PLA melting into the tube above the bondtech gear.  It was my fault - I hadn't tightened the gear to the motor well enough.  I was trying to fix the issue and got hot PLA up above the gear where it stuck.

My fix was to put a small drill down from the top and it got the PLA out.  However, my filament sensor no longer works.  I can print though so it is OK for now.  I'm going to reprint the parts above the gear and fix it at some point.

Posted : 26/08/2019 3:02 pm
Tim
(@tim-m30)
Illustrious Member
Posted by: eyals

The extruder motor gets a lot of heat, which makes the PLA melt before entering the PTFE tube - hence causing the jam.

A MK3S operating in a normal air conditioned room does NOT have this issue.  When operated in enclosures, or in rooms that are not air conditioned and that approach 35c, then they have issues with PLA filament.

The motor operates at 30c to 35c above ambient.  At 25c, the motor can reach 60c.  This is NORMAL for high torque stepper motors in applications that demand high holding torque.   In hot rooms, or enclosures, air temps will reach 35c, the motor will reach 70c, enough to soften PLA.  It gets even hotter inside enclosures.

It is a fitness for use problem.   If you buy a car without air conditioning, you can't complain driving through a desert is uncomfortable and blame the manufacturer.

 

It is always wise to get more than one opinion......
Posted : 26/08/2019 8:51 pm
scottsh liked
Nick-i3mk3s
(@nick-i3mk3s)
Eminent Member

@tim-m30

Point taken, Tim. However when I bought the Prusa MK3S I wasn't told it would require an air-conditioned room to work reliably. I live in a small flat without air-conditioning, so inevitably when I'm cooking the temperature indoors goes up quite a bit. I would consider that normal operating conditions for a consumer appliance.

I don't expect a Prusa to operate over the full industrial temperature range, but I do expect it to work during British summers.

Posted : 22/10/2019 7:43 am
Tim
(@tim-m30)
Illustrious Member

The printer is rated to 40c (I think I read that somewhere).  If you live in a flat that hits 35c or higher when cooking, well, you are pressing the limits, even then, 75c won't melt PLA to the point it flows and puddles, that takes an even higher temp.   

If you have the printer inside an enclosure in that same room, you are exceeding its limits - doors open, or not - simply not enough airflow.

And it isn't the printer failing, it is the plastic you are trying to use.

It is always wise to get more than one opinion......
Posted : 22/10/2019 9:23 am
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