Mini+: Filament grinding/stuck and under extrusion
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Mini+: Filament grinding/stuck and under extrusion  

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Mini+: Filament grinding/stuck and under extrusion



I've been having issues with filament grinding and unser extrusionno extrusion for the past couple of weeks with the Prusa Mini+ that I've only owned for a couple months.

I'll outline quickly below the steps I have taken, please message if there is something crucial that I should be doing.

1) Cleaned extrusion cogs, attempted again and clogging. Noted that if it is able to extrude normal during purging step of filament loading, it will clog by the time the first layer of a print is being made.

2) Take apart the extruder and clean thoroughly. Use bery thing needle to unclog hotend. Still getting underextrusion/no extrusion.

-> Assumed this was a clogged hotend or dueu to the humidity of the room affecting filament, therefore clean hotend in chloroform for 12 hours and dry filament in vacuum oven (PLA filament) at 40 degrees celcius.

2) Filament still being grinded, so take apart extruder and careful clean out entire section.

->Considered that the filament was maybe too far gone and that vacuum oven drying nmay not rectify this. Purchase new spool of smae filament (clear PLA).

3) New filament also clogs in similar manner. Again take apart the extruder and clean and investigate hot end for clogs, can't visibly see anything.

-> Temperatures have been increasing as we approach summer, the room it sits in is usually around 25 degrees celcius. Consider that the filament may be getting to warm in the spool/extruder and therefore too soft. Therefore place spool in bag of silica and put in -80 freezer for an hour to cool.

4) Still nothing. Could be that the filament already heats up too much in the extruder but also not sure that this is the issue.


I have tried different amounts of "clamping" within the extruder of the filament but this doesn't seem to effect the under extrusion. Any tips or insights or questions would be very very much appreciated.

Lou in the lab

Posted : 18/06/2021 10:50 am
Michaël Fortin
Estimable Member
RE: Mini+: Filament grinding/stuck and under extrusion

You didn't mention doing some cold pulls, did you try that?

I recently noticed frequent (but not critical) under extrusion on my MINI+. I had to tweak settings for filaments that used to print perfectly before. At first I just bumped the extrusion multiplier a bit to compensate, not being sure if I was imagining things. After my printer fully clogged on a standard, known-good spool of PLA I knew something was definitely wrong.

I had done some regular maintenance cold pulls recently and only printed PLA afterward so I was pretty sure the hotend was reasonably clean. For my usual cold pulls I used the shorter "unscrew the Bowden tube, cold pull and screw the Bowden tube back on" method. So, no removing the hotend PTFE tube.

However, when opening the hotend to fix this clog I decided to do a more thorough cleanup by removing the hotend PTFE tube and performing a cold pull without the hotend PTFE tube as optionally suggested in step 4 of the hotend disassembly procedure here. This removed a quite large chunk of black (burnt?) plastic from the nozzle which hadn't been removed with my regular cold pulls. By the way, I didn't see any of that black goo when looking inside the hotend from the top with the PTFE tube removed, so it must have been stuck lower inside the heat break / nozzle.

I did the whole shebang from the procedure after that, this time (unscrewing the heat break set screws, pushing the heat block up to compress the PTFE tube, etc.) and I also took the time to reposition my PINDA using the credit card method here just in case my pushing the heat block up caused too big a nozzle height difference (plus my PINDA was a bit too low which meant I was uncomfortably close to -2.0 Live Z with the textured sheet).

After that, everything started working perfectly again! Perfect extrusion at 1.0 extrusion multiplier and no clogs for a print that failed twice in a row just before that.

As a bonus, somehow I also had uneven first layer issues since first receiving my (pre-built) MINI+. Lines on the far-right were always much less "squished" on the sheet than those in the center and on the left. That issue seems to be magically fixed, now. I can only assume it was because my PINDA was slightly angled (not perfectly vertical) before and when adjusting it I made sure it was as vertical as I could get it to be (still not perfect, but close). I don't know enough about how PINDA works to know with absolute certainty if that was what fixed this specific issue, though the timing seemed to indicate so.

I hope this helps!

Posted : 18/06/2021 8:24 pm
Michaël Fortin
Estimable Member
RE: Mini+: Filament grinding/stuck and under extrusion

Too late to edit my post, but I also replaced the hotend PTFE tube with the included spare just in case. It seemed a tad longer which should help to get a good seal through compression.

Oh and don't forget to run first layer calibration after all that, especially if you pushed the heat block up and/or adjusted the PINDA sensor height!

Posted : 18/06/2021 8:48 pm