MMU3 with MK4 Unable to Load to Extruder
Bought the MMU3 and I finally received it after 4 weeks. I printed the parts myself (R4 version) as instructed using PETG. Initial calibration succeeds and I can get filament pre-loaded, however when doing a load test to the extruder it consistently fails for all five filaments. I have done the following:
- Upgraded bother MK4 printer and flashed the MMU3 with the most recent 6.0.1 firmware
- Tweaked the idler tension as much as I could (as per the instructions the top of the screw head is a little bit higher than the top surface), I even put it a little bit lower and flush which made no difference
- To rule out a buffer issue I took the tubes coming out of the MMU3 and freely held them in my hand (to rule of resistance issues) while the loading test sequence was carried out
- When I insert the filament and then initiate the pre-load sequence the MMU3 does successfully "grab" the filament when it gets close enough to the bearings.
- I have tried multiple types of filament
- Mostly used spool of Prusa white
- Silk Blue Matter Hackers
- Silk Purple Matter Hackers
- Brand new unopened spool of Azure Blue Prusament
- From the above tests the only one that I can oddly get a successful load to extruder test is the Silk Blue Matter Hackers because this spool is 3/4 used and is quite brittle. The actions of the MMu3 unit load testing end up splitting the filament. All the other filaments I can never get a successful load to extruder test, which is quite appalling considering the brand new spool of Prusament Azure blue does not work.
- I have made the sure the tip is cut at the appropriate angle
- Checked for nozzle clogs but heating up the nozzle to PETG temps and sticking the included needle (with the original MK4) up the nozzle hole
- Checked the selector for loose filaments
Right before converting to the MMU3 I successfully printed the MMU3 parts with PETG with zero issues so the printer in stock form works.
RE: MMU3 with MK4 Unable to Load to Extruder
apart from initial load to MMU, where you say the MMU Grips the filament,
You have told us what doesn't happen, but not told us what does happen.
SO I will take you at your word, that the filament does load to the MMU
Have you got the correct filament sensor on the Mk4 Nextruder?
Have you got the standard length PTFE Reverse bowden tube between the MMU3 selector and the Nextruder?
Have you calibrated the Mk4 Filament sensor with the MMU Filament sensor in place?
https://help.prusa3d.com/guide/10a-mk4-setup-and-calibration_426826
Step 15
when you load the filament to the Nozzle the MMU Should forward the filament through the selector into the reverse bowden all the way to the extruder, when the nextruder should start turning in preparation for the oncoming filament the filament should slow as it moves into the filament sensor and when the filament sensor , senses the presence of the filament, the MMU should disengage the idler and allow the extruder to control the filament. (You should actually see the Idles lock/swivel /filament sensor assembly move to the left, when the filament is engaged.
If the sensor is not adjusted correctly, the extruder will spit the filament out and it will be pulled back to the MMU by the MMU pulley wheel and idler assembly
If the filament is accepted by the filament sensor, the nextruder should feed it through to the nozzle satisfactorily...
Is any of this happening on your printer?
If the MMU3 to extruder ptfe is too long, because some people use non standard setups, the feed to extruder may timeout and fail...
I have never used it, but I understand there is an option to specify a new length for the PTFE
Good luck, Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
RE: MMU3 with MK4 Unable to Load to Extruder
I am using all stock parts (including the tubing) that comes with the MMU3.
This is what happens specifically:
I am at the preflight checks. All the calibrations pass with green check marks. I am able to preload each filament but the problem lies with the Load Test.
This is what happens: Feeding to FINDA > Feeding to drive gear > Feeding to fsensor > Disengaging idler > Unloading to FINDA > Disengaging idler. It repeats this process three times then displays LOAD TO EXTR. FAILED. It provides the error code which I visit the QR Code link. None of the suggestions help and although the link is focused around the MK3S+ the suggestions relevant to the MK4 don't work.
I can see the filament travel tube between the FESTO fittings and it seems all fine but apparently not. I don't notice it snagging on the lower FESTO fitting. All grub screws are confirmed tight and on the flat part of the shaft. I don't notice any "chewed up" filament collecting.
RE: MMU3 with MK4 Unable to Load to Extruder
Hi, I Understand that this is frustrating. and sorry if I seem to be asking silly questions.
I Can't see the printer and my crystal is not working very well... so I am doing my best to guess what's going on.
In the sequence
Feeding to FINDA > Feeding to drive gear > Feeding to fsensor > Disengaging idler > Unloading to FINDA >
does the filament sensor indicator ever switch to on?
or does it always show off?
What you describe suggests that the filament sensor is not being activated although I would have expected to see a filament sensor error instead of a LOAD TO EXTR. FAILED.
Is your nextruder nozzle firmly installed in the correct position? If it's low, the filament may catch on the edge of the tube rather than feeding smoothly into the top of the nozzle feed tube.
Since you rebuilt the printer with the MMU Filament sensor, new idler sides and new epicyclic gearbox mainplate
Have you tried turning the MMU Off and loading the filament manually into the extruder bypassing the MMU? if so did it work?
If not, could you try it?
totally silly thought... is the filament temperature above 170C when the filament is loading? to the best of my knowledge, this is the cold extrusion cut off temperature if the temperature is too low, the extruder will simply, not extrude. certainly on the Mk3, there would not be any warning, I have to admit, I have not tried it on My mk3.9 and I don't have a Mk4 to try
Mk3.9 and Mk4 us the the same extruder setup, so the comparison should be valid.
That's all i can think of at the moment...
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
RE: MMU3 with MK4 Unable to Load to Extruder
The temperature isn't involved here. I am conducting the pre flight checks of the MMU3. Part of that is pre preloading the filament to the MMU3 then doing a Load Test for each filament. It just loads the filament to the Extruder to make sure.
- The nozzle only goes up so far. See attached picture. I feel like the filament is getting caught on the bottom FESTO fitting into the Extruder and inducing friction. I'm not sure how to fix that because I have made sure the PTFE tube is all the way in the FESTO fitting.
RE: MMU3 with MK4 Unable to Load to Extruder
Wasn’t the I.D. Of the Festo fittings increased with the switch to the MMU3?
Could you possibly have used the old, smaller one at the Nextruder?
Good luck. It will work perfectly when you get it sorted out.
RE: MMU3 with MK4 Unable to Load to Extruder
Yes, festo's were drilled out
https://help.prusa3d.com/guide/10a-mk4-setup-and-calibration_426826
see section 21 photo three. 
IIRC, Mine have a Yellow Spot on the side
Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
RE: MMU3 with MK4 Unable to Load to Extruder
Apologies everyone for wasting your time. I have been 3D printing for several years and still made a "newbie" mistake. Apparently the top of the Nozzle was utterly clogged where no filament could get through. I tried to heat up the nozzle to PETG temps and inserted the needle underneath but could not remove the clog towards the top. I eventually disabled the MMU3 unit, unscrewed the top FESTO fitting into the Extruder and did a normal load + purge. Low and behold a giant blob of white filament came out the bottom. Unfortunately it appears with the MMU3 enabled the ability to do those sorts of things are limited.
Once I removed the clog the Load Test passed every time. I was then able to print the "test sheep" successfully.
Thanks again for everyone's help.
RE: MMU3 with MK4 Unable to Load to Extruder
I am pleased to hear that the issue is now resolved.
Happy Printing
Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
RE: MMU3 with MK4 Unable to Load to Extruder
I had the same issue and the fix was ignoring the MMU3 build instructions and tightening the tension screws more to make it easier for the filament to enter...