Print fails at the same place. Filament ground away against gears so no traction.
I recently bought a Prusa MK3S and assembled it very slowly and double checking every single step. Printer worked great. After about a week I had a jam in the PTFE tube. I disassembled the hot end, heated it up, and pulled the filament out of the PTFE tube. Recalibrated and everything worked okay.
Check out the pictures here: https://imgur.com/a/ZLOEUFt
Had another jam. Did the same fix, recalibrated, but now all my prints fail. I tried printing gear cubes in PLA three times and they fail at about the same place. The first print shows the failed print. The second shows the same with a previous print below it with different infill. Both stopped printing at about the same place. The third pic shows how the filament is ground away against the gears and has no traction to extrude. If I heat it up I can unload the filament so there's no jam.
As the last keychain pic shows, If I print something else the quality is terrible and inevitably results in a blob or failure. The extrusion quality is terrible.
I have tried both loosening and tightening the idler assembly and got the same results. In the last picture of the keychains I tried lowering the speeds and dropped the print temperature but it still comes out terrible. PLA Filament came with the printer and previously worked great and is less than a month old. Any ideas? Please help!
Best Answer by lindharin:
I had a similar problem with some miniature garbage cans that I wanted to use for tabletop gaming. I got the model off thingiverse, and they had very thin walls (needed to have thin wall detection turned on in the slicer or it missed parts of the walls) and the wall design involved a lot of retraction at certain heights. It would consistently under-extrude at the retraction-heavy layers, assuming it didn't just jam entirely. I had the same issue with other prints, but more randomly - this garbage can mini was the one that was 100% consistent with problems.
It was also the only print I found that failed with PETG. Other than that one model, I generally found PETG was less sensitive to the heatbreak issue because of its higher melting point temperature, so if you have any PETG filament, give that a try and see if you have less trouble. Just be aware that even it can have this same problem with a slow enough flow rate (models with very thing walls or geometry causing slower feeds) and retractions. Some people have had success by lowering or disabling retractions. I never actually tried that myself; I wanted to fix the issue, not just find a workaround.
Anyway, when the print jammed at that layer of the garbage can model, if I was nearby and could quickly unload the filament before the jam got too bad to prevent easy unloading, I'd find that 2.2 mm bulb that Tim described, an indication of the heatbreak issue being the cause. If you want more details, the heatbreak issue is fully described in a thread started by Antimix, and Tim (and others) go into a lot of detail about the causes in that thread. The symptoms they identified matched my experience, so I was pretty confident that it was causing my issues with this model as well as others. So I went ahead and replaced the heatbreak with a standard E3D version (my notes on that process are in this thread) and printed the garbage can perfectly the first time with PLA in the new heatbreak.
RE: Print fails at the same place. Filament ground away against gears so no traction.
Your heat break is causing the problem. You can print hotter - much hotter. Reduce retraction to zero. Or replace the heat break with a standard E3D-V6-175 model (avoid the Prusa modified version that jams).
If you have an MMU, well, replacing the heat break may cause other problems.
RE: Print fails at the same place. Filament ground away against gears so no traction.
I'm a novice so I'm still trying to understand all the variables. If it were the heat brake, wouldn't the problems have shown up from day one? It printed fine until the second clog. Why would it have a problem printing now and not earlier?
Or, why would it print fine for an hour and then fail at the roughly the same place? Thanks for your help. I appreciate the reply.
RE: Print fails at the same place. Filament ground away against gears so no traction.
Extruding plastic takes two things: proper nozzle temperature and force applied to the filament. If the gears applying the force begin grinding into the filament, that means something is preventing flow out the nozzle. And if the nozzle temperature is adequate, then a plugged nozzle is the most likely problem. It can also be something pinching the filament along it's path - either inside of outside the extruder (spool binding, bad collet in the heat sink). And it can be an artifact of the heat break design that has a step that can cause jams. As you can see, there are only a few few things that can cause what you are experiencing. You stop the print, unload the stub, clip it off, reload teh filament and reset the clock for the next attempt. If you reload the stub, you'll have jamming almost immediately.
So starting with the basics:
Is that by chance glow-in-the-dark filament?
Have you verified the nozzle is maintaining temperature?
Have you done a cold pull or two to rule out hard debris or material in the nozzle?
... why does a print start fine then fail at about the same place every time? The pumping action of retracting and de-retracting the filament forces melt up the filament. This melt eventually gets far enough up the heat break to reach the transition zone - the area between the heat sink and the heater block. Here, the Prusa heat break has a small step, from 2.2 mm to 2.0 mm. When the melt reaches this step, it expands to the new 2.2 mm diameter, and continues to flow up around the filament. At some point the melt cools and hardens into a 2.2mm mushroom that will no longer move past the 2.2>2.0 mm step. The extruder tries to push, but instead just chews the filament; making loud clicking noises as it grinds away.
RE: Print fails at the same place. Filament ground away against gears so no traction.
I had a similar problem with some miniature garbage cans that I wanted to use for tabletop gaming. I got the model off thingiverse, and they had very thin walls (needed to have thin wall detection turned on in the slicer or it missed parts of the walls) and the wall design involved a lot of retraction at certain heights. It would consistently under-extrude at the retraction-heavy layers, assuming it didn't just jam entirely. I had the same issue with other prints, but more randomly - this garbage can mini was the one that was 100% consistent with problems.
It was also the only print I found that failed with PETG. Other than that one model, I generally found PETG was less sensitive to the heatbreak issue because of its higher melting point temperature, so if you have any PETG filament, give that a try and see if you have less trouble. Just be aware that even it can have this same problem with a slow enough flow rate (models with very thing walls or geometry causing slower feeds) and retractions. Some people have had success by lowering or disabling retractions. I never actually tried that myself; I wanted to fix the issue, not just find a workaround.
Anyway, when the print jammed at that layer of the garbage can model, if I was nearby and could quickly unload the filament before the jam got too bad to prevent easy unloading, I'd find that 2.2 mm bulb that Tim described, an indication of the heatbreak issue being the cause. If you want more details, the heatbreak issue is fully described in a thread started by Antimix, and Tim (and others) go into a lot of detail about the causes in that thread. The symptoms they identified matched my experience, so I was pretty confident that it was causing my issues with this model as well as others. So I went ahead and replaced the heatbreak with a standard E3D version (my notes on that process are in this thread) and printed the garbage can perfectly the first time with PLA in the new heatbreak.
RE: Print fails at the same place. Filament ground away against gears so no traction.
I just wanted to say thank you for such a thoughtful, detailed response. I did three hard pulls and every one of them had the "knob" at the end you described. I don't have calipers handy to measure the exact size, but your explanation makes sense. I've started reading the original antimix thread where you describe what's going on. In the meanwhile, I've ordered a standard E3D V6 1.75 BREAK and will install it shortly; Hopefully this will resolve the issue. Thanks again for such a great reply and helpful advice.
RE: Print fails at the same place. Filament ground away against gears so no traction.
Thanks for the thoughtful reply. I don't have any PETG handy so the machine is down at the moment. I've ordered the replacement heat break and will install it shortly. That post of yours with the heat break installation guide is outstanding and will definitely come in very handy when I go to do the install. I was thinking of many of the exact same questions. Likewise, reading through the original discussion of the issue is very helpful. I really appreciate your taking the time to reply and give such helpful advice.
RE: Print fails at the same place. Filament ground away against gears so no traction.
I ran into a similar issue shortly after I got my MK3S. I did one print with my retraction set way to high (4 or 5mm I think). This caused the filament to get stuck in the PTFE tube about 1/3 of the way through the print and the extruder gears ground the filament in half. I managed to extract the broken pieces from the PTFE and got it to extrude again. I then set my setting back to Prusa standard (retraction 0.8mm) and did about an 18hour print of a container. About 80% into this print, I came back to the print to see that the filament was stuck again and again ground in half by the gears. This time it was stuck so hard that I had to remove and replace the PTFE tube. However, even after that I couldn't get the filament through the tube - the heat-break was clogged up. I look my hot-end completely apart, heated it up, poked it with needles, but nothing seemed to clear the blockage. The trick that finally let me clear it was to buy some 1/16" (~1.58mm) metal rods, heat up the heatbreak and the heatsink by themselves (taken out of the extruder head, nozzle removed, and without the fan blowing on them - make sure you remove the PTFE tube and the collet before you do that or they will melt - I learned this the hard way), and sticking the metal rode through the heat-break a few times to push out all the blockage.
After doing this, I re-assembled the hot-end, adding thermal grease on the heat-brake threads going into the heatsink. I believe it's possible that the thermal compound that was there before (which was solid) was not as good or was not in as-good contact with the threads and allowed the cold end of the heat-break to get too hot. This is likely to blame for the melting in the 0.22 to 0.2mm transition that's specific to Prusa. I initially thought that I may also have to switch to a standard heat-break. However, after doing all of this and re-calibrating the printer, I have been printing trouble free for over 100 hours without a single blockage. I printed at 50um resolution and 200um resolution, with lots of retractions and standard retractions and everything works great now. So I have a suspicious that, when assembling the E3D hotends, Prusa doesn't always achieve the best thermal contact to between the heat-break and the heat-sink. The silicon thermal grease seems to solve this issue, at least for me.
RE: Print fails at the same place. Filament ground away against gears so no traction.
I ended up taking the advice others gave and just replaced the Prusa heat break with a standard E3D heat break. During the disassembly I noticed there was almost no thermal compound present in the interface between the heat break and the heat sink. I couldn't find any thermal compound that was specific to the typical heat ranges (most didn't list temps at all) used on the Prusa printers so I just ended up going with CPU thermal compound. So far it's been rock solid. I had one additional jam shortly after swapping out the heat break but it was quick to disassemble and fix. After that it's been running flawlessly. I don't know if the issue was just the heat break design defect, lack of thermal compound, or both, but I'm very satisfied now that it's running correctly. Glad to hear yours has been reliable now as well.
RE: Print fails at the same place. Filament ground away against gears so no traction.
@rgshah01
I'm running into the same problem. Can you tell me which of the standard E3D heatbreak you purchased? 1.75mm or 2.85mm? Also, what thermal compound did you use?