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Clogged Hotend Problem and Solution  

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ZigZagZuggurat
(@zigzagzuggurat)
New Member
Clogged Hotend Problem and Solution

Hello dear forum,

After running the printer with a PLA job overnight on stealth mode, with a total rate of about 50% I woke up to discover that the extruder had jammed!

After opening the little extruder door, it seemed that the plastic being fed into the hotend had gummed together and had starter to wrap around the extruder gear axle. I recognized this as heat creep; but from where I'll speculate later and invite your comments.

First I had to clear this jam. I realized that I would have an easier time extricating the blob and filament rather than trying to force it down. I turned off the fan checks, stuck a bit of PLA into the extruder fan to stop it (couldn't find an option in the menus... maybe I should look again). I heated the hot end up to 250C and tried to pull the blob with some pliers, but part of it had cooled in the very top parts, so this just broke off... I tried pushing from below with the accupuncture needle but the cold part on the top would not budge upwards. The PLA had sheared parallel to the surface of the interior of the chamber so not even tweezers could be used. I tried the reccomended push-through method described in the book, because now at least that blob was out of the way, but the same issue of the top of the plug being cold meant that I couldn't quite push it through.

What worked?

taking a soldering iron with an adjustable output and setting it such that it would just start to melt PLA. I fed the filament through normally and let some hang out of the door. Using the warm (not full power) iron, I warmed up the tip of the PLA and then deftly set it against the exposed PLA surface. Once I was happy with the orientation, I pushed gently as the plastic cooled and solidified. I held this for about a minute or more, blowing out the dust that had built up in there and trying to cool it off. I pulled on this (gradually) and out came that pesky portion, which had also confirmed that the plastic had gone under the extruder.

So next time you have a jam and your situation is like mine, try a weld extrication with the same exact material.

What caused it?

I have some ideas:

  1. The extruder motor runs warmer than the others (near-constant use of course), and that heat might be transferring into that inner chamber
    1. Solution: cool the motor. Add heat fins to the top and/or another fan.
  2. The printer is in an enclosure intended for ABS plastic (IKEA Lack table case), but the front face is open. The ambient heat rises in there, no doubt.
    1. Solution: cool the chamber/extraction fans
  3. The extruder tension was improper; if it was too tight it may have been working the motor too hard and contributing to (1) and causing the problem.
  4. The print job had too many retract commands and/or was on the big side and deserved babysitting. It was making four narrow towers with low infill (10%) when it jammed. Perhaps the constant retracting helped heat the filament up before it reached the nozzle.

What do you all think? Thanks in advance.

Posted : 22/05/2019 1:47 am
gnat
 gnat
(@gnat)
Noble Member
RE: Clogged Hotend Problem and Solution

Unfortunately this is a known issue with PLA when using an enclosure. Just leaving the enclosure open seems to work for most, but that really depends on the ambient temp of the room and air flow into the cabinet during the print.

Nice trick with cleaning it out. I don't think I've seen that before (usually it's pulling the extruder apart if you can't otherwise clean it up).

MMU tips and troubleshooting
Stop SL1 tank leaks with a simple o-ring...
Posted : 22/05/2019 2:32 pm
Nigel
(@nigel)
Honorable Member
RE: Clogged Hotend Problem and Solution

Look to a post by 3D Printing Nerd and PLA clogs on MK3S.  It seems the Prusa MK3 /S comes with a custom E3D heat-break  for Prusa and the MMU, fitted as standard across MK3 printers. That has a 2mm to 2.5 mm throat to allow for swap out of filament for the Multimaterial System. He had someone replace his heat-break with a 2mm all metal throughout throat.  It solved the issues. Also it was the part cooling fan it seems cooling the hotend by 5 deg C also. So a silicone sock was recommended. This was an issue with some Proto Pasta HTPLA. A member of Proto Pasta did the research.  I will just try using a silicone sock for now. 

 

Nigel
Life is keeping interested and excited by knowledge and new things....
Posted : 22/05/2019 11:55 pm
Nigel
(@nigel)
Honorable Member
RE: Clogged Hotend Problem and Solution

I have just finished my Prusa MK3S build. I will be running preflight checks after I have checked wiring to the Einsy.  Tomorrow. 

Nigel
Life is keeping interested and excited by knowledge and new things....
Posted : 23/05/2019 12:15 am
gnat
 gnat
(@gnat)
Noble Member
RE: Clogged Hotend Problem and Solution
Posted by: Nigel

Look to a post by 3D Printing Nerd and PLA clogs on MK3S.  It seems the Prusa MK3 /S comes with a custom E3D heat-break  for Prusa and the MMU, fitted as standard across MK3 printers. That has a 2mm to 2.5 mm throat to allow for swap out of filament for the Multimaterial System. He had someone replace his heat-break with a 2mm all metal throughout throat.  It solved the issues. Also it was the part cooling fan it seems cooling the hotend by 5 deg C also. So a silicone sock was recommended. This was an issue with some Proto Pasta HTPLA. A member of Proto Pasta did the research.  I will just try using a silicone sock for now. 

 

All true, but his issue is the extruder motor heating the gears and softening/melting the PLA and gumming the top of the extruder up.

The heat break issue is responsible for jams down lower. 

MMU tips and troubleshooting
Stop SL1 tank leaks with a simple o-ring...
Posted : 23/05/2019 12:16 am
Nigel
(@nigel)
Honorable Member
RE: Clogged Hotend Problem and Solution

Ahh ok. Fair enough. Thanks for the reply. I will sit back and read more. I am new back to Prusa with a MK3S.  My MK2 I passed onto a group that needed it a year or so ago for railway modelling.

Nigel
Life is keeping interested and excited by knowledge and new things....
Posted : 23/05/2019 12:21 am
joseph.c41
(@joseph-c41)
New Member
RE: Clogged Hotend Problem and Solution
Posted by: @zigzagzuggurat

Hello dear forum,

After running the printer with a PLA job overnight on stealth mode, with a total rate of about 50% I woke up to discover that the extruder had jammed!

After opening the little extruder door, it seemed that the plastic being fed into the hotend had gummed together and had starter to wrap around the extruder gear axle. I recognized this as heat creep; but from where I'll speculate later and invite your comments.

First I had to clear this jam. I realized that I would have an easier time extricating the blob and filament rather than trying to force it down. I turned off the fan checks, stuck a bit of PLA into the extruder fan to stop it (couldn't find an option in the menus... maybe I should look again). I heated the hot end up to 250C and tried to pull the blob with some pliers, but part of it had cooled in the very top parts, so this just broke off... I tried pushing from below with the accupuncture needle but the cold part on the top would not budge upwards. The PLA had sheared parallel to the surface of the interior of the chamber so not even tweezers could be used. I tried the reccomended push-through method described in the book, because now at least that blob was out of the way, but the same issue of the top of the plug being cold meant that I couldn't quite push it through.

What worked?

taking a soldering iron with an adjustable output and setting it such that it would just start to melt PLA. I fed the filament through normally and let some hang out of the door. Using the warm (not full power) iron, I warmed up the tip of the PLA and then deftly set it against the exposed PLA surface. Once I was happy with the orientation, I pushed gently as the plastic cooled and solidified. I held this for about a minute or more, blowing out the dust that had built up in there and trying to cool it off. I pulled on this (gradually) and out came that pesky portion, which had also confirmed that the plastic had gone under the extruder.

So next time you have a jam and your situation is like mine, try a weld extrication with the same exact material.

What caused it?

I have some ideas:

  1. The extruder motor runs warmer than the others (near-constant use of course), and that heat might be transferring into that inner chamber
    1. Solution: cool the motor. Add heat fins to the top and/or another fan.
  2. The printer is in an enclosure intended for ABS plastic (IKEA Lack table case), but the front face is open. The ambient heat rises in there, no doubt.
    1. Solution: cool the chamber/extraction fans
  3. The extruder tension was improper; if it was too tight it may have been working the motor too hard and contributing to (1) and causing the problem.
  4. The print job had too many retract commands and/or was on the big side and deserved babysitting. It was making four narrow towers with low infill (10%) when it jammed. Perhaps the constant retracting helped heat the filament up before it reached the nozzle.

What do you all think? Thanks in advance.

That worked (using the soldering iron to splice the the nub that was flush with the PTE tube) like a charm (was using PLA when it jammed).  Thank you for posting

Posted : 09/03/2020 5:20 pm
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