PLA printing - constant extruder blockages  

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Ondrowicz
(@ondrowicz)
Eminent Member

I have a big problem with PLA printing and starting to be pretty mad about it.

When I bought the printer (about half a year ago), I started my first prints using PLA and everything was OK. However, I should say that most of the prints were pretty simple and not too extensive.

Then I switched to PETG, most prints perfectly OK. But recently I switched back to PLA and started to have regular issues with it. I observe underextrusion to no-extrusion situations pretty often so when I start a print and come back after a while, the printer head moves in the air above the model torso. I observe these situations for different filament manufacturers (Prusament, Mladec, DevilDesign) and different filament colours.

Based on the available forum discussions, I have already tried this:

  • to check correct position of the extruder gear and the tightness of its screw, to clean it by a brush and to lubricate the teeth
  • to disassemble the hotend, exchange the PTFE tube and to apply a new thermal conductive paste
  • to clean the nozzle before print by a needle and by performing a cold pull
  • to exchange the original Prusa heatbreak to a normal full-metal heatbreak (one bore diameter, without the slight increase of diameter at the PTFE end) and using the original thermal conductivity paste and a new 0.4 mm nozzle
  • to measure the resistance of the thermistor at the room temperature to check its proper function
  • to calibrate PID
  • to change the extrusion temperature to higher values (lower values fail for me in general, when I try to print a temperature tower going from higher to lower temperatures, the print usually fails at about 205°C or lower). I keep the bed temperature at 60°C.
  • to decrease retraction from 0.8 to 0.4 mm, also decreasing the speed of de-retraction from 35 to 25 mm/s
  • eventually to disable retraction to 0

I use a good model to test the system now (a moon lamp, Thingiverse object no 4102658, white PLA filament by Filament-PM), with a lot of retractions, so with non-optimal settings the print fails pretty soon. It should be said that for other more "technical" prints where there is a lot of fast extrusion and only a limited number of retractions the print fails happen not so often.

With the original Prusa heatbreak, it was more difficult to unload the filament after the fail, apparently due to a small "blob" of the filament appearing in the extended part of the heatbreak. Now with the normal heatbreak, the unload is easy. I also tried different degrees of extruder idler tension. Before, I always used the approach of "the lightest tension just to start the filament to move and add about half a turn", when I use this approach now, the extrusion is OK for a while but then the extrusion stops, the motor moves on but the gear is slighty grinding the filament. When I increase the tension, the clicking eventually starts. The temperature of the extruder motor is quite high (barely able to hold it in my fingers) but I think I read this is OK for this motor, the gear has similar temperature. The temperature of the heatsink is quite normal, lukewarm.

I am just about to start to print extensively from PLA (parts of a car model), now I am not sure what to do. The temperature of the room with the printer is about 25°C I guess. I know that it would be better to have a colder place (I do not have one) but is it really only the effect of ambient temperature? Or am I missing something else which is important?

I am starting to be pretty annoyed and from the forum discussions I have a feeling that I am not alone. Am I supposed to buy a different printer to be able to print such a basic material as PLA without the need to spend numerous hours of investigations??

Posted : 09/05/2020 9:38 pm
Ondrowicz
(@ondrowicz)
Eminent Member

Just in the case someone has the same problem and is therefore interested, here is a (maybe temporary) solution to my problem:

  •  temperature: 220°C hotend, 60°C bed
  • retraction decreased to 0.4 mm and the speed of retraction and deretraction to 10 mm/s
  • extruder idler pressure increased to optimal value according to the instructions
  •  but perhaps the most important aspect was to introduce a dust filter, with a small piece of sponge with a drop of oil to clean and slightly oil the filament going into the extruder

With this settings, I already successfully printed several objects, each print lasting some tens of hours. The dust filter/oiler was the last thing I wanted to install but I must admit it works well.

This post was modified 3 months ago by Ondrowicz
Posted : 18/05/2020 9:13 pm
bobstro
(@bobstro)
Illustrious Member
Posted by: @ondrowicz
  • [...] extruder idler pressure increased to optimal value according to the instructions

Can you elaborate on this? You want the extruder idler just tight enough, not overly tight. On my Mk3, the screw protrudes roughly 1mm once tightened sufficiently.

  •  but perhaps the most important aspect was to introduce a dust filter, with a small piece of sponge with a drop of oil to clean and slightly oil the filament going into the extruder

I'm glad this is working for you, and I'm not going to argue with you about it, but be aware that oil can contaminate your PEI print surface and cause adhesion problems down the road.

With this settings, I already successfully printed several objects, each print lasting some tens of hours. The dust filter/oiler was the last thing I wanted to install but I must admit it works well.

That indicates that lubrication helped, which raises questions as to why you're getting excessive friction. Idler tension can certainly be part of that. Be sure the idler gear can rotate freely without obstruction. Check the filament path for friction and alignment. 

You didn't mention your ambient printing temps, but using an enclosure or room approaching 40C can reduce the efficiency of the air cooled hotend design. This is a common cause of problems with PLA as the filament softens and causes the extruder to do more work.

 

My notes and disclaimers on 3D printing and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan...
Posted : 18/05/2020 9:45 pm
Ondrowicz
(@ondrowicz)
Eminent Member

As for the idler tension, I use exactly the same setup you described. Actually, my previous tension was too weak.

For me, the filter and oil is certainly not the optimal solution and I am planning to do more testing in order to get rid of it, not only because of increased contamination of the print surface but also because I do not believe it has absolutely no adverse effect on the quality of the printed object.

The temperature could play a role, my biggest problems emerged when the ambient temperature was about 25°C or even slightly more, now it is a little bit colder (22-23°C). I have no box for the printer.

Posted : 19/05/2020 11:25 am
bobstro
(@bobstro)
Illustrious Member

I can't point to anything specific, but give some thought to heat build-up and what might cause it:

  • Excessive retractions.
  • Poor airflow around the hotend.
  • Filament feed path friction (stuck idler gear, path misalignment, blockage)
  • A PID tune is always a good idea to help with temperature consistency.

Was yours a kit? If you dive more into the hotend, common issues are:

  • Lack of thermal paste at the top of the heatbreak, between the heatbreak and heat sink (cooling fins) and not between the heatbreak and nozzle.
  • Heatbreak replacement to eliminate 2.2-2.0mm step (you've done this).
  • Remove any fan grilles or other unnecessary impediments to airflow.
  • Improve air circulation around heatsink.

Other than these, it's hard to suggest much more without seeing what's going on. Give it a good visual inspection, check tensions and possible hangups for filament. Test fans, ensure they're assembled correctly (esp. for a kit).

 

My notes and disclaimers on 3D printing and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan...
Posted : 19/05/2020 2:18 pm
Ondrowicz
(@ondrowicz)
Eminent Member

Yes, I have done most of the things you suggested. I am quite sure the heatbreak is installed correctly, I have disassembled/assembled it several times, applied the thermal paste on the correct end used the paste supplied by Prusa.

I plan to do one additional test (and if the system improves, hopefully I will be able to get rid of the filter/oiler) once I receive a bimetal heatbreak which I already ordered.

Posted : 19/05/2020 8:55 pm
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