Load/Unload issues - some tips that helped me
I battled with the MMU for the better part of 4 days having to fix load/unload issues almost after every tool change. I tried all sorts of things (such as messing with the tension screws, cleaning the hobbed pulleys, and dis/reassembling parts of the MMU) but I think the three most important things were:
DOUBLE CHECK ALL OF YOUR PTFE LINES
Make sure that the filament can go through smoothly. You should be able to push it through holding the filament lightly. If you have to pinch it and push hard there's something that can be improved. For me I found that I had tightened the plate from section 6, step 15 too tightly: https://help.prusa3d.com/en/guide/6-electronics-and-mmu2s-unit-assembly_44728#45328. This caused feeding line through the MMU to be just a bit too hard and so loading and unloading constantly got bungled. Also make sure that your spools are nicely positioned and roll easily and that none of your filament is kinked.
CHECK THE FINDA POSITION IN THE SELECTOR
A bunch of my failures seemed to be a case where the filament would be unloaded perpetually.... It would be pulled out of the extruder, through the selector, across the pulleys and back into the supply PTFE lines but the pulley motor would never stop. I messed around with jiggling the steel ball in the selector and that seemed to work (stop the unloading) a couple of times. Then I checked the LCD > Support > Sensor Info > FINDA and wondered if maybe it wasn't going from 1 to N/A or 0 quickly enough. I re-read this: https://help.prusa3d.com/en/guide/5-pulley-body-assembly_43152#44360 and decided to try adjusting the FINDA while printing with filament loaded. I turned/pulled the FINDA up a bit making sure to keep the reading in "Sensor Info" at 1. I ultimately ended with the metal part of the FINDA 15.9mm exposed above the printed part.
MAKE SURE YOUR FILAMENT TEMPS ARE CORRECT
If you use the default "Generic PLA", etc. it may not match the manufacturer recommended temperature. In a couple of cases I had filament where the temp was too high or too low by default and that resulted various issues when pulling the filament out of the extruder. Take the time to configure your filaments in PrusaSlicer so that they have the right temps. Doing this seemed to stop leaving "strings" or having the filament end be "knobby".
Hope this helps someone.
Andy
Loading Unloading
Aharbick,
Is this the issue that you were having?
My printer will not load from the MMU2 but when I unscrew the PTFE tube from the extruder and hand load the filament, then it will load. My issue seems like a software/firmware issue between the two (MK3 and MMU2) that keeps the filament from loading all the way to the bondtech gears. Either this, or the filament is in the bondtech gears and the MMU2 does not allow free pull by the extruder.
@parkerdingeldein
That is a problem with the filament sensor in the extruder. you need to re adjust that sensor. https://help.prusa3d.com/en/guide/8-preflight-check_47224#231204
The MMU should stop loading filament when the filament sensor(ir sensor) is triggered. You can see that the filament gets between the bondtech gears as the idler door slightly opens. That should trigger the sensor and stop the MMU loading the filament and stop the extruder trying to pull in more filament for a moment.
You can see that the extruder is waiting all the time for the sensor to trigger even when you unscrew the ptfe tube and push in filament by hand.
The sensor never gets triggered.
MAKE SURE YOUR FILAMENT TEMPS ARE CORRECT
If you use the default "Generic PLA", etc. it may not match the manufacturer recommended temperature. In a couple of cases I had filament where the temp was too high or too low by default and that resulted various issues when pulling the filament out of the extruder. Take the time to configure your filaments in PrusaSlicer so that they have the right temps. Doing this seemed to stop leaving "strings" or having the filament end be "knobby".
Prusaslicer changes the temperatures depending on what printer you select (MMU2s or MMU2s Single)
I had the same problem with some filament as you describe. Even some times with Prusament.
The filament can need some tweaking, but most of the time I now change the temps back to the temps for MMU2s Single and have better tips on the filament after unloading.
I use a lot of filaments from Real-Filaments and these work better with higher temps where Prusa is lowering the temps when using the MMU.
Try to factory reset BOTH the printer and MMU
@parkerdingeldein
I have had that exact issue (and probably even shot a video just like yours), but more recently than this original post and frustratingly because I ruined a hotend trying to fix it. Subsequent to replacing the hotend it happened again and I was about to lose my mind when I think I figured something out.
In both of the cases I had upgraded firmware on the printer and/or done a factory reset for some reason. The firmware on the MMU hadn't changed so I didn't think I needed to do anything with it. But most recently when I resolved the issue all I did was factory reset the printer AND THEN factory reset the MMU.
It's kinda a pain because then you have to recalibrate everything including your sheets but it worked for me. For reference here's the article on how to factory reset the MMU: https://help.prusa3d.com/en/article/factory-reset-mmu2s_1920
Configure your spools
but most of the time I now change the temps back to the temps for MMU2s Single and have better tips on the filament after unloading.
Yep 100%... I took the time to setup spools in PrusaSlicer for all of my different filament spools to make sure that it uses temps that I want.
Filament loads to nozzle and then unloads
I am a newbie to 3D printing but a long time designer and manufacturer.
When I added the MMU2S to my MK3S+ I have had filament tip unload issues (which I am working on). Today when trying to print, the filament will load to the nozzle extrude the small smear prior to the initial wipe and then it UNLOADS.
Has anyone experienced and solved this please?
RE:Filament loads to nozzle and then unloads
Pretty sure your sensors are not calibrated correctly. There are some tips on how to do this, e.g. here: https://help.prusa3d.com/en/article/ir-filament-sensor-calibration-mmu2s_2245
the topic has already been discussed several times:
wbr,
Karl
Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen.
RE:Filament loads to nozzle and then unloads
Thank you Karl, the post you linked is almost a perfect description of the issues I am experiencing. I will follow that advice and see what eventuates. I will update on progress within a few days.
RE:Filament loads to nozzle and then unloads
Ok, I've been watching the filament sensor during a print and have seen erratic behavior from the filament sensor as long times "0" and long times "1" . If I apply a load to the chimney it stays as "1". I will begin here until this is perfect. I also noticed the PINDA go from "1" to "0" and this might be a concern as well (idk).
Possible way to prove IR sensor erratics
I have set my FS action to "pause" I am hoping this will prove the issues I have
RE:RE:Filament loads to nozzle and then unloads
@karl-herbert
I did calibrate the IR Sensor and I also checked the value when inserting the 1.5mm Allen Wrench prior to making the video. My IR sensor is working correctly, but I think the lever action is activating too soon. Are you saying that I need to trim the trigger in the chimney that is near the IR Sensor? How is this considered a defect in the product it there is an issue?
Are you saying that the IR Sensor is activated properly, but the filament is not fully engaged in the bondtech gears?
Here are my thoughts (mostly for my own sake), and I hope to try this out this week.
I think the issue is that the IR Calibration suggestion is using the 1.50 mm allen wrench and the filament is ~1.75 mm which is ~0.25 mm different. It may be that because the filament is larger than the calibration instrument diameter, the filament will tend to be partially loaded when the IR sensor is fully activated. If the gears stop (see video 0:08) because they sense the filament (which the filament is making contact with the gears) the Calibration is correct in that it allows sensing of the filament. The problem that I need to see ( and need to test out) is if the calibration method is imprecise because it is sensing too small of a diameter.
Must be perfect mating surfaces for chimney and tower
I found, after sitting down and looking properly at it the chimney/tower/lever/IR sensor all need to be fitted and mated perfectly. It is not a casual assembly. It is possibly the single most critical assembly required to load filament correctly.
The full magnet lever assembly should be removed from the extruder assembly when upgrading to the MMU2S, not just the old filament guide.
The new components MUST be examined and ANY artifacts or burrs MUST be removed cleanly.
The new push in guide MUST be inserted and FLUSH or no more than 0.5mm below the extruder body.
THIS REQUIRES FILING AND CHECKING WITH A STRAIGHT EDGE
The chimney assembly needs to fit over the push in guide flush with NO gaps, I emphasize NO GAPS This is critical well.... all these steps are critical really 😉
The IR sensor also needs to sit perfectly in its seat and the lid also needs to sit perfect, I emphasize again PERFECT FITMENT
All components require cleaning with a knife and a file and emery.
Before final assembly, and with the lid removed from the sensor, check the free movement of the lever, continue checking this lever action with a small length of filament, holding the IR sensor in place whilst the chimney and tower assembly are installed, also continually checking the sensor monitor for the "0"-"1" change.
The lever assembly must travel freely and fully into the gap between the sensors, trim the thin piece very carefully, with the lid off the sensor this can be evaluated easily. It is MINIMAL removal.
Hope this isn't too long winded but honestly, this assembly must fit perfectly for it to work.
This has now given me zero interventions during load/unload unless my tip formation is not correct.
For correct tip formation, I also found on github some filament profiles for the MMU2S which are proving very useful with the tip formations on my stock Prusa extruder assembly. I have tried the eSun profiles on Prusament PETG and Prusament PLA with success so far
https://gist.github.com/Klathmon/59adf6450e1decddbae792137a05d95b
with thanks to Klathmon
RE: Extra Loading Distance Setting Slic3r - Grinding MMU2
@baklin and @karl-herbert
No, my sensor was fine, it was triggered; however, I did adjust it and the MMU2 co-operated again for two days. Then loading crashed again and I was frustrated and tried adjusting the sensor and the Chimney timing like @karl-herbert suggested. That did not work to fix it again. Then I waited until today and I discovered the >Printer Settings< under Prusa slicer thanks to 0Calvin on YouTube's video "Victory over the MMU2".
He suggested that to fix the ramming or fighting that was happening at the extruder gears (hence the "grinding" sound in the video) would be fixed by changing the Extra Loading Distance of -13mm (-25 mm in my case) to 0 mm to end the Olympic struggle at the extruder.
@terence-3 I think the timing might be this "Extra Loading Distance" setting in slicer.
Thanks y'all for the time and replies.