Used MK3S, dropping turds of filament, causing crashes: solutions?
As in the title, it's a used MK3S, sold as having "layer shift" issues and a bad filament sensor. Filament sensor seems fine and the layer shift issues might still be lingering, though a little TLC on the stepper and pulley seems to have done some good. But I don't think that's what I am seeing here.
My issue now is that the extruder is dropping turds on the work pieces and provoking crashes (on X and Y), to where the nozzle/printhead tears pieces off the print bed. It's a sound I have come to know all too well. Bed adhesion is not a problem, Live Z calibration came in at -1.65 today (I reran it just to be sure that wasn't an issue) and the pieces that have completed look great on the bottom. From a Prusa official video, it seems I need to set the idler door screw/extruder gear offset such that the extruder, run my hand from the LCD, sends filament through the nozzle. No more, no less. I have had some issues with under extrusion/that annoying clicking and occasionally printing nothing in midair. Is over-extrusion an issue? I don't think there is a leak or misfitted heat break/nozzle.
Filament has been sealed and humidity is not an issue at the moment.
Hw big are they A picture might help, also a picture of the hotend/nozzle assembly from two different angles.
Cheerio,
RE: Used MK3S, dropping turds of filament, causing crashes: solutions?
RE: Used MK3S, dropping turds of filament, causing crashes: solutions?
Improperly assembled hotend and nozzle. You have a gap inside the heat block between the heatbreak and nozzle, resulting in no seal. This allows plastic to work it’s way up and down the threads and pool until it drips onto the part during printing.
It needs stripping down, cleaning of all the excess plastic and then reassembling correctly.
Agreed. Pay particular attention to the diagrams at the bottom of this page:
https://help.prusa3d.com/en/article/changing-or-replacing-the-nozzle-mk2-5s-mk3s-mk3s_2069
Cheerio,
RE: Used MK3S, dropping turds of filament, causing crashes: solutions?
Interesting. This is the second of these that has passed through my hands with this problem, both factory assembled. I'll take a look at the docs.
RE: Used MK3S, dropping turds of filament, causing crashes: solutions?
I think the cause of this might be calendar-time / heat creep. I overtook responsibility of some heavily used MK3 printers at the office and started them up after them being dormant for a like 2 years. I had exactly the same problem, with "turds" of filament. The cause was the same, everything not being tightened enough (I think I had a leak between the nozzle and the heaterblock).
RE: Used MK3S, dropping turds of filament, causing crashes: solutions?
This one was a bit dusty so it may have been idled for a bit. But this gap is the issue, from what I am reading? I need to heat the machine up and snug that up with no gap. And I suppose I could remove and clean the nozzle…all that burned on filament probably isn't helping.
RE: Used MK3S, dropping turds of filament, causing crashes: solutions?
No, that gap is NOT the issue. Completely different gap. Please study the page Diem linked to further. That is the gap for the clamp that holds the heater cartridge in place.
We are talking about a gap that you can not see from the outside. Inside the actual heater block. The heater block besides holding the heater cartridge is in effect a big threaded nut. You screw the heatbreak in from above and then you screw the nozzle in from below.
The heatbreak and the nozzle meet inside the heater block and seal against each other inside the threaded hole. If the nozzle and heatbreak don't press against each other perfectly and with the correct torque then there wont be a seal. Filament is extruded under pressure and that pressure WILL cause it to flow both up and down the thread. So you will get melted filament on both the top of the heater block and around the nozzle.
Thats why the instructions for fitting a nozzle will usually talk about a gap between the nozzle hex area and the heater block. That gap is visible as its outside. If you can screw the nozzle all the way in and the hex part is touching the heater block then it hasnt reached the heatbreak. If you screw it in and it reached the heatbreak and you can still see that you would be able to screw it in more then its at least butting up to the heatbreak. You then torque it up at full temp to ensure its tight.
When they get into this state you must ensure that the nozzle and heatbreak surfaces are clean and smooth/damage free as those are the surfaces that are pressing against each other. Scratches are potential leak vectors so don't use damaged parts. If you have left over plastic between the 2 then will also stop them sealing. The idea is to ensure that no plastic can get between the 2 in use.
RE: Used MK3S, dropping turds of filament, causing crashes: solutions?
This makes it more clear, thank you.
The heater block besides holding the heater cartridge is in effect a big threaded nut. You screw the heatbreak in from above and then you screw the nozzle in from below.
Now I wonder much of this I have to disassemble to get to the bits I need to work on. And while it's at temperature as well.
RE: Used MK3S, dropping turds of filament, causing crashes: solutions?
@frebys, was your fix as straightforward as a re-tightening or was there more to it? The challenge I face is getting to grips with that nozzle, since it's encrusted with filament. I don't mind wrenching but I generally have the motor off and cool when I do it.
getting to grips with that nozzle, since it's encrusted with filament. I don't mind wrenching but I generally have the motor off and cool when I do it.
Once it's at full nozzle-change temperature the encrustation will be soft enough to squidge aside as you work. I use a plain 7mm spanner for the nozzle and a 17mm, very thin, bicycle spanner to hold the block in place.
When it's off you can allow it to cool before you inspect the problem and make a clean-up plan.
You may as well replace the nozzle with a new one which will have a clean surface, most people encounter this issue when replacing a worn nozzle. The amount of cleanup really depends on how long it was left to ooze - and whether the previous owner attempted to fix it by overtightening without cleaning out the cooked plastic.
Cheerio,
RE: Used MK3S, dropping turds of filament, causing crashes: solutions?
@frebys, was your fix as straightforward as a re-tightening or was there more to it? The challenge I face is getting to grips with that nozzle, since it's encrusted with filament. I don't mind wrenching but I generally have the motor off and cool when I do it.
My fix was just a matter of re-tightening it, but I preceded that by doing a big clean-up. I heated up the nozzle and used a bunch of paper towels to wipe all the plastic off (being careful not to burn myself). So when I did the actual re-tightening, everything was virtually clean.
If I was in your situation, I would consider just purchasing a new nozzle / heater block. I think on the MK3 you can check how many meters of filament it has printed (somewhere in the settings). Nozzles have a limited lifespan based on how much they have printed, so if the amount printed is really high you might want to purchase a new nozzle regardless (I don't know the lifespan of nozzles, but I'm sure you can find that out quite quickly by just searching online).
PS: I left my old job a few months after the 3D printer was fixed, so I can't tell you how well the 3D printer held up in the long-term, but I think it was working just fine.
I don't know the lifespan of nozzles
At a typical 30% - 50% duty cycle with standard PLA/PETG and no abrasives reckon on 6 - 9 months; expect to recalibrate your first layer 'Z' offset twice in that time as the nozzle wears down.
Cheerio,
RE: Used MK3S, dropping turds of filament, causing crashes: solutions?
So based on that, a new nozzle is warranted. The mileage (filament usage) was erased, from what I recall when I looked into it. Based on the state of it, I would assess it as having been used like a taxi, driven all day, every day.
They can take it - as long as you keep on top of maintenance a Mk3 is good for several years active printing ...
Cheerio,
RE: Used MK3S, dropping turds of filament, causing crashes: solutions?
Well, I just did this little task. The nozzle doesn't fit any socket, metric or Imperial, that I have, from 7mm to 5/16" so that's something to look into. It was difficult to get the nozzle screwed in with vise grips with the heat break moving freely. It would great if the heat break had some affordance that could be safely gripped, ie, that wasn't wrapped in tiny thermistor wires and stout power wires. Calibrating and cleaning up now. I'll order some spare nozzles in known sizes, I guess.
??? is this a genuine E3D nozzle? There are some 'clones' out there that do not quite fit correctly.
Cheerio,
RE: Used MK3S, dropping turds of filament, causing crashes: solutions?
??? is this a genuine E3D nozzle? There are some 'clones' out there that do not quite fit correctly.
I have no way of knowing that. It came with the machine.