Filament sensor triggering for no reason
I’m having an issue on my XL where the filament sensor trips mid-print for absolutely no reason. It all seems clear as well, no filament buildup or blockages.
Anyone else seen or troubleshot this issue on their XL yet?
Fairly annoying on an overnight print to have stopped one hour in, though!
RE: Filament sensor triggering for no reason
Having the same issue but worse. I convinced Tech support to send me a new Side Filament Sensor and it did correct the problem temporarily but now it appears that a replacement Tool Filament Sensor is needed but Tech support is very relunctant to go there making me jump thru too many hoops. Now the Filament test is failing altogether.
Not very happy with Mr. Prusa right now!
RE: Filament sensor triggering for no reason
Literally had this happen to me last night, right around 200 hours of print time total. I disassembled the sensor and what looks like what happened is the groove the filament sits in has worn to be "actually round" versus the 3d printed steps caused by the layer heights. This puts it right at the limit of the switch the detent presses and depending on how it wiggles can read open or closed.
Temp fix is just unplug the sensor, as then it reads that there's filament in there (not a big deal if you know you're not going to run out on the spool and just want the print to finish). I'll try a repair later by putting some tape (not sure what kind) in the outer groove for it to ride in.
RE:
Literally had this happen to me last night, right around 200 hours of print time total. I disassembled the sensor and what looks like what happened is the groove the filament sits in has worn to be "actually round" versus the 3d printed steps caused by the layer heights. This puts it right at the limit of the switch the detent presses and depending on how it wiggles can read open or closed.
Temp fix is just unplug the sensor, as then it reads that there's filament in there (not a big deal if you know you're not going to run out on the spool and just want the print to finish). I'll try a repair later by putting some tape (not sure what kind) in the outer groove for it to ride in.
Just happened again to me, but this time on the print head sensor, which was really odd. I reset the printer and checked a bunch of things, and finally found the issue. The filament I was using had a thin section, about half the thickness it should be, in a spot of just a couple of inches. Not sure if that happened because of the dryer being too hot and it stretching or a manufacturing defect (not prusament), but cut out that one spot and it started acting as expected again. The filament was too thin to properly actuate the switch, so it made sense why it was triggering. Earlier when I was inspecting I didn't notice the small thin section.
RE: Filament sensor triggering for no reason
Happened to me before two times, but today 3 times!!! Always had to cancel the print. What is odd that it happened always at the same time of the print and it happened when the tool head is in the rear right area. It looks like the previous layer had already feed issues at the same spot because there were signs of under extrusion in that layer.
I'm using the grey Prusament, assuming that is not a filament issue. Just an educated guess from this observation: Could it be that the friction is getting too high in the pipe to the tool head when the tool head is in the rear right area. This in combination with high environment temperature (like now) lead then to a stretching and thinning of the filament in the pipe which then triggers the sensor at the tool head?
I move to print now the the front area (one tile) and while writing this it passed the problem area without false triggering the sensor. Also no sighs of under extrusion like before. I guess this need further investigation.
RE: Filament sensor triggering for no reason
After having the last print without any filament sensor issue in the front area of the print bed, I used "repeat last print" on the XL menu and the filament sensor triggered again at that front area. After I finished the filament change process the print appreas broken (that's why I always had to cancel the print before), but looking more closely what the XL does (see pictures), I guess it continues the print at a higher layer not having proper contact to the top layer. It probably printed a while without recognising that there is no filament flow anymore, before triggering the sensor. That might be supported by the look of the filament I took out when the sensor triggered. Makes sense? I did now increase the pressure on the extruder springs a bit.
Happened to me before two times, but today 3 times!!! Always had to cancel the print. What is odd that it happened always at the same time of the print and it happened when the tool head is in the rear right area. It looks like the previous layer had already feed issues at the same spot because there were signs of under extrusion in that layer.
I'm using the grey Prusament, assuming that is not a filament issue. Just an educated guess from this observation: Could it be that the friction is getting too high in the pipe to the tool head when the tool head is in the rear right area. This in combination with high environment temperature (like now) lead then to a stretching and thinning of the filament in the pipe which then triggers the sensor at the tool head?
I move to print now the the front area (one tile) and while writing this it passed the problem area without false triggering the sensor. Also no sighs of under extrusion like before. I guess this need further investigation.
RE: Filament sensor triggering for no reason
Some more pics. The second pic shows again some under extrusion in the support area of the objects in the rear rows. 
RE:
The filament shouldn't be squished so much by the extruder gear. On first glance it looks as if your spring pressure is wayyy too high. Not an XL owner yet, but that doesn't look healty.
If that is not the case, can you somehow check if the extruder gear gets hot? I'm not sure if it can happen with the Nextruder, but if something is wrong with your hotend cooling (e.g. fan mounted backwards or airflow obstructed), or if your extruder motor runs too hot, on some printers this becomes an issue.
Another thing I would check is if one of the gears slips. It's one of the most common reasons for random extrusion issues, and progressively gets worse until fixed.
RE: Filament sensor triggering for no reason
I agree, it shouldn't look like this. The odd thing is that it only looks like this, when the filament sensor has incorrect triggered. Normally the filament looks OK like on the pic. But could not yet find the real reason for it and it's still happening to me from time to time, but only with the 0,6 nozzle. I printed a lot of pieces in Prusament PETG carbon fibre and the hardened 0.4 nozzle (with adaptor), not happened a single time. BTW, the quality is much better compared to Prusament PETG and the 0.6 nozzle. I always used to presets which came with the PrusaSlicer. See the comparison on the pics (Pic 3 Prusament PETG CF with 0.4 nozzle and Pic 4 Pusament PETG with 0.6 nozzle; key caps are always printed with the SL1). I got a lot of artefacts on surfaces with the 0.6 nozzle and also realised measurements are not 100% accurate, e.g. holes are 0.1 - 0.2 mm to tide in direct comparison to the 0.4 nozzle.
I checked the fans, they work both. The are also no blockings as far as I can see. For the temperature of the extruder gear I can't say, but will measure it when it happened next time. (Will be a challenge, because I usually realise the false triggering when the nozzle heating as been switched off already for long time.) But, seeing the facts a hot extruder gear sounds like a valid reason. Still not sure why the sensor triggers though. BTW, I also found one day a tiny grub screw on the print bed. I know there is another post on this, but my 3 screws in the heat-block are all in. So currently I have no clue were this came from.
Keep you posted.
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BTW, I also found one day a tiny grub screw on the print bed.
Uh, oh. If that is the one fixing the main gear to the motor you might have your culprit. I don't know how this looks exactly, but the motor axle will have a flat side for sure. If the gear keys in to that it would still work without the grub screw, but will wobble to the side under pressure because it needs clearance to be pushed on. Just guessing though. From your filament picture I cannot really tell if the material was compressed or eaten away by the gear.
It really sounds like the 0.6 builds up too much pressure while the 0.4 doesn't. Temperature a bit too low for 0.6? It could also be down to a broken nozzle (maybe a manufacturing defect). How does it look when you remove the filament & shine a light through it?
Edit: A simple thing you can do without fiddling around is measure the grub screw and ask chat where it belongs.
RE: Filament sensor triggering for no reason
Thank you for the hints. The grub screw topic is resolved! I found it and the tech support in the chat confirmed it. It was for the heatsink thermistor and sits on the bottom next to the hole for the nozzle. (You can only see it if the nozzle it out.) So maybe the other issues are related to it, because of incorrect temperature sensing of the heatsink. I also ordered some other 0.4 Nextruder nozzle for some more tests. Keep you posted.
BTW, I also found one day a tiny grub screw on the print bed.
Uh, oh. If that is the one fixing the main gear to the motor you might have your culprit. I don't know how this looks exactly, but the motor axle will have a flat side for sure. If the gear keys in to that it would still work without the grub screw, but will wobble to the side under pressure because it needs clearance to be pushed on. Just guessing though. From your filament picture I cannot really tell if the material was compressed or eaten away by the gear.
It really sounds like the 0.6 builds up too much pressure while the 0.4 doesn't. Temperature a bit too low for 0.6? It could also be down to a broken nozzle (maybe a manufacturing defect). How does it look when you remove the filament & shine a light through it?
Edit: A simple thing you can do without fiddling around is measure the grub screw and ask chat where it belongs.
RE: Filament sensor triggering for no reason
Assuming the fan speed is controlled by the heatsink temperature reading, it's actually possible this resolves your problem. Filament gets sticky if the heatsink gets too hot, which increases resistance gradually. It would explain why 0.4 works better, because filament is fed more slowly. Fingers crossed!
RE: Filament sensor triggering for no reason
Thank you and yes I guess it did the trick. Made two long running test prints (2 times 9 hours) and not a single false filament sensor triggering 😅. Also the print quality with the 0.6 nozzle is normal again after the clamp "totally running out of shape" disaster from 2 days ago as you can see in the pictures. Just look at the edge. What to say other than "small thing, but big impact" 😃. Building up XL experience 👍
RE: Filament sensor triggering for no reason
Thanks, that is good to know. I hope PR does something about these grub screws, there seem to be quite a few cases on the forum where one went missing. If you hadn't found yours it would have been very hard to narrow down. Happy printing 🥂
RE: Filament sensor triggering for no reason
To fully agree, while understanding that there is a double challenge. Constant material expansion through heat changes and of course vibration e.g. when printing infill at high speed. Typically Loctite Treadlocker should be used for such applications but not sure if it can be used for these temperatures. Furthermore a very precise torque rate should be given by PR for assembling (and used by PR as mine was pre-assembeled).Torque should be high enough to avoid accidentally unlocking but not too strong in order to avoid damaging the sensor. BTW, talking about it, I'm also missing (or could not find it) the assembly instruction for the tool head on the Prusa3D Website. I strongly advise to add it, if not available yet. It would have help me in the first instance, when the screw fell of. Thank you Prusa!!!
RE: Filament sensor triggering for no reason
My guess is it happened on the plane if you live across the pond, or wasn't tightened at all during assembly, for whatever reason. If any frequencies that happen during printing would be involved, they would have noticed during prototype testing.
This is exactly why I prefer kits 😉
RE: Filament sensor triggering for no reason
This is exactly why I prefer kits 😉
Me too. Brought my MK3S+, MMU2 and SL1 also as kit and did the SL1Speed upgrade myself, which was basically almost a new build. I actually also preordered my XL semi-assembled, but changed last minute in order to get it faster 🤪. Now I'm waiting desperate for the multi-tool extension promised, but unfrotunately still not available.
RE: Filament sensor triggering for no reason
BTW, also designed and build the enclosure for the XL myself incl. additional light and camera. Kept the back of the printer with the power supplies outside for better cooling.
RE: Filament sensor triggering for no reason
Update: Received a replacement Nextruder from Tech support but the problem still exist. Tech said they kicked it up to the developers but no response yet. I'm thinking the problem might be related to the logic board. It's been months now and still no resolution!
Any ideas?
RE: Filament sensor triggering for no reason
Hmm. Not sure, but based on my expereice I assume the sensor is very sensitive. I have a kind of idea, but I'm also still not sure why in my case a wrong heatsink temperature could trigger the sensor, but only with the 0.6 nozzle. I even do not know how the filament sensors works in detail e.g. which technology is used. I guess it's the grey ribbon cable coming from the logic board which belongs the the sensor and it sits above the gear. I see a lot of mechanical force (shaking of the tube an filament) in this area when the tool head moves because it's very close to the tube from where the filament gets fed.
How often does it happen? What filament type are you using? Have you tried different types? Have you tried a different nozzles. Did you get a complete replacement tool head? I still assume it's more a mechanical problem. It would really help to analyse and to narrow down the problem, if PR would publish the assembly guide of the tool head.
Update: Received a replacement Nextruder from Tech support but the problem still exist. Tech said they kicked it up to the developers but no response yet. I'm thinking the problem might be related to the logic board. It's been months now and still no resolution!
Any ideas?