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PLA melted by extruder motor in MK3S  

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Wouter Himschoot
New Member
RE: PLA melted by extruder motor in MK3S

Hi guys,

I'm having exactly the same issue for over 1 year now like bycx. As soon as I've created a very nice enclosure, the PLA jammed immediately after 1h printing. Tried with ABS and ABS+, they also jam but after a much longer time.

To be honest, I feel a bit disappointed. Without enclosure my prints warp. Even PLA when printing big parts. In belgium the temperature in my workshop is also going from 10°C in the winter to 25°C in the summer. Therefor an enclosure is really necessary.

I do understand that the extruder gear limit should be max 40°C. I'm hoping that PRUSA can develop an additional part to mount somewhere on the side of the extruder gears, so it can be cooled extra. Standard design now is only cooling the aluminium extruder itself, not above. My PLA always melts just at or below the extruder gears. Mostly I have to disassemble the whole extruder :-s

To only way I guess is to install a fan on the gears, with a tube which goes outside the enclosure backside and sucks in cold air for cooling. Will try to make this...

Posted : 01/04/2020 3:42 pm
Eminent Member
RE: PLA melted by extruder motor in MK3S

Hello inf-97.

Things to check on your MK3S:

  1.  your hotend cooling fan is mounted the correct way round and that the channel and hotend's heatsink fins are all clear of dust and print debris
  2. that you've run a hotend PID calibration and a Heatbed PID calibration inside the print enclosure when it is over 30°C
  3. did you put some heatsink compound on the screw portion of the heatbreak that screws into the heatsink part of the hotend.
  4. ensure that you've used the correct MK3s version of the hotend PTFE tube rather than the MK3/MK2/MK2S version. The lengths are different.

I'd look at maybe adding an e3Dv6 silicone sock over the hotend heater block and rerunning the hotend PID calibration as this will also reduce the energy required to keep the hotend at temperature.

We live in a part of Australia that regularly goes from below 0°C in winter to over 40°C in summer so we also use an insulated temperature controlled enclosure with air filter for our Prusa MK3S for PLA (indoor), ABS and ASA (outdoor) prints.

Posted : 02/04/2020 11:01 am
Wouter Himschoot
New Member
RE: PLA melted by extruder motor in MK3S


Hi, thanks for the quick reply. BTW, just changed to my real name instead of this  weird nickname... 

1. installed correctly for sure and works ok

2. never done a temp calibration. That would be a very good thing to do. Have a calibrated fluke temp meter.

3. never disassembled the heatbreak itself from the extruder assy. Its factory default from Prusa.

This week i'm running daily prints of about 7hrs straight with Prusament PLA. Today I have installed temp sensors everywhere. The enclosure is 15°C inside and pretty constant even when printing for 3hrs already. The extruder motor however, always wants to go hotter and hotter when I close the enclosure door. When i leave the door open with a gap of > 3cm's then the extruder motor temperature is going a bit down or stable. Like this Im keeping it stable at 45 °C. When Im closing the door completely -> goes up constantly.

This is exactly what I've read on other peoples comments. Some people have add an extra fan on the extruder motor and also installed a sock. Guess that's my next project 🙂  I wanne keep my extruder motor and bondtech gears at +- 40°C inside the closed enclosure.
Thanks for the reply from Australia !

Posted : 02/04/2020 11:45 am
Peter M
Noble Member
RE: PLA melted by extruder motor in MK3S

The printer is made to print without enclosure, so if you print pla leave the door open, and all the way open.

This post was modified 2 years ago by Peter M
Posted : 03/04/2020 5:39 pm
Active Member
RE: PLA melted by extruder motor in MK3S

I’ve been having similar issues since I assembled my mk3s in September 2019- frequent jams apparently caused by heat melting/softening the filament on the bondtech gears but I get this problem without an enclosure. 

I feel like I have tried everything by now: got the original E3D  heatbreak, applied thermal paste to it twice (just to be sure), I did the CG-Tech mod of mounting a fan on the extruder motor, tried printing in an air-conditioned room at 20c, replaced the ptfe tube, have a silicone sleeve on the heater block, tested 4 different brands of Pla, different retraction lengths and idler door tensions. Nothing solved mu problem. I can't even print a Benchy as included in the SD card.

PETG prints fine. I just don’t like all the stringing and would rather print with a bioplastic.

All in all I am very disappointed with my mk3s. I've spent more time trying to fix it than I have printing.

I have posted recent tests and pictures in detail in this thread:

Any suggestions will be greatly appreciated. Please help. This printer is driving me nuts.

Posted : 06/04/2020 11:42 pm
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