Underextrusion with filament grinding
For context, I've owned an MK2S, three MK3S, and two Prusa MINI+ printers prior to the single Prusa MINI+ that I own now (due to an international move, where I needed to downsize and bring only what I could carry with me).
On my previous two Prusa MINI+, they both eventually experienced the "click of death" where the extruder would start clicking, and it would underextrude. I believe this was due to heat creep, and in both cases, replacing the heat break with the Bondtech heatbreak fixed the problem.
I built my current MINI+ from a kit. It has always been temperamental; I've struggled with it chewing up filament and turning it into dust basically since it was new. PLA on parts with minimal retractions do the best (but can still fail), and PETG with only a few retractions fails regularly. To fix the problem I have:
- Checked the entire filament path for any pinches, hangups, and snags. It seems perfectly smooth all the way through
- Taken apart the extruder many times to make sure it is clean, correctly assembled, and that the filament path aligns with the hobbed gear
- Tried tightening up the extruder tensioner
- Tried loosening up the extruder tensioner, even to the absolute maximum adjustment
- Replaced the stock heatbreak with the part from Bondtech
The only idea I have left is to remove the filament sensor, but filament does seem to smoothly pass through it when I test it.
I am completely out of ideas, and pretty frustrated with the machine. I've taken apart the extruder so, so many times to clean out filament dust from failed prints that I can basically do it with my eyes closed. I feel that the only option I have left is to buy a Bondtech extruder, which feels like an extreme step. I've always bought Prusa because they historically have "just worked", but I feel truly stuck now.
Is there anything I am missing? Perhaps try another hobbed gear from Prusa?
Best Answer by PotatoFi:
I've replaced the thermistor in my Prusa MINI+, and I tossed all of my 1+ year old filament, and it's printing like a dream again. So, here's where I've landed:
For the click of death, where the extruder motor "clicks" as it fails to push filament through the hotend, this is fixed either by repasting the heatbreak, or replacing the heat break with an upgraded one from Bondtech. This is normally about €11, but it is currently €16 for some reason.
For filament grinding, where the extruder seems to grind through the filament and stop pushing it through, try raising the hotend temperature by 10-20°C. If that seems to "fix" the problem, then it could be that your hotend thermistor is drifting low at higher temperatures. Replace the hotend with a new one from Prusa.
RE: Underextrusion with filament grinding
Right out of the gate I had the gear in the extruder come loose from the motor shaft (just got my first ever 3D printer and Prusa last month so still new) not sure how feasible it is for you but I went ahead and upgraded to the Bondtech IFS extruder ... tho getting the tension on the thumb screw can be confusing ... for the hot end went ahead and did the whole slice engineering copperhead heat end ... finally found some presets on printables that seem to work .... guy name Reeder ... plus slowed down the printing ... just seems trying to utilize the input shapers thing and print fast doesn't always produce a "clean print" ... and the Z-Axis brace seemed to help ... but you'll having extruder issues .. duh
RE: Underextrusion with filament grinding
I believe someone had similar issue recently, so worth to look recent topics (say last 3 months).
If the extruder grinds the filament no matter if the tensioner is pushing soft or hard then usually it means the filament does not melt properly - check the thermistor and bump nozzle temperatures by 10C or slow down the print by 50%.
Check if you can extrude without extruder, push the filament by hand from extruder to the nozzle. Check the path between the extruder to the nozzle for obstacles of any form and if the short PTFE tube is properly chamfered and compressed.
See my GitHub and printables.com for some 3d stuff that you may like.
RE: Underextrusion with filament grinding
I may be on to something. On a whim, I bumped the temperature up by 10° on some of my pretty-new and cheap-o filament. I just got a perfectly good print out of it. I am wondering if my thermistor is drifting. It does read the exact same temperature as the bed when I let everything cool down, but it could be that the temperature deviates as it gets hot. I've ordered a replacement from Prusa (only 10€ and I wanted filament anyway), and will report back in a couple of weeks with my findings.
RE: Underextrusion with filament grinding
Recently I had temperature shooting to 300C in a second because cables were having some issues, reseated the cables so they are not squeezed and it works like a charm. May need to replace thermistor, though.
Check the cable connections between the thermistor and the cables that go to the mainboard, they may be clamped and thus may got loose or some residue there causing incorrect readings when cables are bent during printer movements.
See my GitHub and printables.com for some 3d stuff that you may like.
RE: Underextrusion with filament grinding
I'm about 5 prints in, and I've found that going over temperature by 20°C is the sweet spot. At room temperature (about 24° these days), the bed and hotend match, so my theory is that the hotend thermistor temperature drifts at higher temperatures, not at room temp.
A new thermistor arrives from Prusa tomorrow. I'll replace it and really find out for sure.
RE: Underextrusion with filament grinding
I've replaced the thermistor in my Prusa MINI+, and I tossed all of my 1+ year old filament, and it's printing like a dream again. So, here's where I've landed:
For the click of death, where the extruder motor "clicks" as it fails to push filament through the hotend, this is fixed either by repasting the heatbreak, or replacing the heat break with an upgraded one from Bondtech. This is normally about €11, but it is currently €16 for some reason.
For filament grinding, where the extruder seems to grind through the filament and stop pushing it through, try raising the hotend temperature by 10-20°C. If that seems to "fix" the problem, then it could be that your hotend thermistor is drifting low at higher temperatures. Replace the hotend with a new one from Prusa.