MMU stops feeding filament before pinch roller grabs it
Using Load to Nozzle, the filament feeds quickly from the MMU, slows down after the Front PTFE Length, triggers the filament sensor, but then stops feeding before the pinch rollers in the extruder can get a grip on it.
The picture above shows the final position of the filament. The door was only opened after it was clear that NO filament was being extruded.
Tried re-calibrating the filament sensor a couple of times. No effect.
Tested a wide range of tension on the pinch roller springs. No effect.
If I manually push the filament in, I can get it to engage the pinch rollers and extrude properly.
What can I adjust to fix this problem?
RE: MMU stops feeding filament before pinch roller grabs it
Also spent some time making nice tapered tips, thought the shape of the filament might make a difference, it does not.
What controls the "ramming" that is supposed to make nice tips? Core One does ramming at the end of "load filament to nozzle" and again during "unload filament".
Occasionally load filament works. Like 1 time in 8.
Is there any way to change the alignment between the festo where the filament enters the extruder and the pinch rollers? I don't see any way to change it.
RE: MMU stops feeding filament before pinch roller grabs it
Firmware 6.3.4+10511
Bootloader 2.4.1
MMU 3.0.3
Buddy 47
RE: MMU stops feeding filament before pinch roller grabs it
In your picture I'd say that filament is far enough in for the Nextruder gear to take over. Have you definitely told the printer that you have done the MMU Nextruder mod?
Settings -> Hardware -> Printhead -> Nextruder
The ramming is controlled in the filament settings in Prusaslicer. In the Advanced section there is a button called 'Ramming settings...' that opens up a configuration window. I had some success in making the rammed tips of my ABS filaments more (totally!) reliable for unloading and loading by reducing the ramming time from the default 1.25s to 0.5s.
RE: MMU stops feeding filament before pinch roller grabs it
My understanding of the need to tell the printer that you have done the MMU Nextruder mod is that this will make the Nextruder gear turn while you are loading filament. The non-MMU filament sensor is easier to trigger by simply pushing filament into the fitting, but the sensor in the MMU conversion needs the filament to actually start moving around the gear before it will move the sensor far enough to trigger it. If the gear isn't moving, it's very difficult for the end of the filament to start sliding round the serrated gear - it CAN be done with a lot of force, but by having the gear rotate it becomes a lot easier. This is why you have to manually begin the 'Load Filament' process with the MMU Nextruder, instead of letting it start automatically by inserting filament into the fitting.
RE: MMU stops feeding filament before pinch roller grabs it
I checked the Settings Hardware Printhead Nextuder and see that it was already set for [MMU], set it back to [Stock] did the filament sensor re-calibration. Power on/off. Set back to [MMU] did the filament re-calibration.
What I see is that during Stock filament calibration the extruder motor is freewheeling and I can insert the filament all the way to the hot end.
During MMU filament calibration the extruder motor is controlled. When the screen asks you to insert the filament, the extruder motor is running and the gear is turning. But the motor and gear stop when the filament is just barely inside the pinch. This is where it collects data on what is the value of the sensor to indicate "fully inserted". Since the motor is controlled, you cannot push the fiber any further into the hot end. The picture shows where the filament sits at that time.
Looking at the Info | Sensor Info | Filament Sensor we can see that with no filament the sensor is around 1800000, when the filament first touches the sensor and is not yet in the pinch we see 572000, and when it is fully loaded into the hot end 254000.
Is there any way to see what values MMU Filament Sensor Calibration uses? Despite many attempts, I still see the filament stop much too soon and not get picked up by the pinch.
My suspicion is the calibrated value is too high causing the sensor to trigger before the filament is inserted enough, like the picture in the original post.
Position of filament loaded during MMU calibration
RE: MMU stops feeding filament before pinch roller grabs it
There is a way to see the calibration values. Can anyone confirm these are reasonable numbers? NoFilament value: 1788786 and HasFilament: PASS value: 561346
If these numbers are Ok then maybe there is noise on the filament sensor, possibly overshoot or some other dynamic of the signal that makes it trigger too soon?
Procedure:
Have a USB stick inserted. Turn on Settings | System | Save Logs to File. Run the calibration. Turn off Settings | System | Save Logs to File. Eject the USB stick, put it into a laptop and locate the logs.txt file.
3543.259s [INFO - FileSystem:7] Started logging to file: /usb/log.txt
3572.911s [INFO - Selftest:10] Started
3576.073s [INFO - Selftest:10] user pressed continue
3587.831s [INFO - Selftest:10] calibrating
3587.952s [INFO - FSensor:16] Calibrating NoFilament value: 1788786
3589.911s [INFO - Selftest:10] calibrated
3589.911s [INFO - Selftest:10] calibrated
3603.747s [INFO - Selftest:10] insertion check has filament
3608.761s [INFO - Selftest:10] user confirmed filament is inserted
3608.811s [INFO - Selftest:10] calibrating with filament inserted
3608.891s [INFO - FSensor:16] Calibrating HasFilament: PASS value: 561346
RE: MMU stops feeding filament before pinch roller grabs it
Little help maybe,
These spring tension screws need to be straight with the end of the thread.
This maybe helps becasue filament does not easy push the sensor to loaded state because springs hold it back.
But it doesn't look like your nextruder is modified for mmu. (sensor + gear case)
old
RE: MMU stops feeding filament before pinch roller grabs it
Thanks Alienbliep! That does look like I have the Old version Nextruder.
Where can I find the New mod? Is this a part I can print?
Regarding the tension springs, I think I have tried every possible variation from very loose to quite tight.
RE: MMU stops feeding filament before pinch roller grabs it
But it doesn't look like your nextruder is modified for mmu. (sensor + gear case)
Good spot!
RE: MMU stops feeding filament before pinch roller grabs it
Where can I find the New mod? Is this a part I can print?
The STLs are available to print - PC-CF is recommended.
https://www.printables.com/model/531604-mmu3-printable-parts/files
From memory I think you'll need a magnet, an o-ring, and a couple of different length screws for the idler.
Instructions here.
RE: MMU stops feeding filament before pinch roller grabs it
Yes.
When you buy the mmu3 new the parts come with it.
When the mmu is used sold mostly the nextruder parts are not included.