RE: "Nozzle Cleaning Failed." Error
@cupu It happened to me when I did not care that during the probing phase that the filament was tensioned. 😓
You must have at least one loop of filament over the Nextruder so that it will never go in tension between the Nextruder and the spool during the probe phase.
If the filament is tensioned it could apply negative force and push up the Nextruder, fooling the pressure sensor, so that the Nextruder goes much more down and break the bed.
No idea of what happens when you have a MMU3 on the MK4. I don't have it, and since there is the PTFE tube in play over the Nextruder, I couldn't say anything.
RE:
Hi @antimix,
That is good info. I apologize, I am not understanding some things (not my native language and so on) so just to be clear, you're saying that:
- In certain situations, if the filament is pulling up on the nextruder it can mess with the load cell (i.e. the loadcell is higher than normal or thinking it's higher but the nozzle is in the same place)
- What do you mean by having a loop of filament over the nextruder? Does that literally mean to have a loop to have extra slack so if the filament tightens up on the spool side then the loop takes that tension (gets "smaller") rather than pulling on the nextruder?
I have the clasic setup of the MK4 inside the prusa enclosure ; so the filament spool is on the top right of the enclosure, it feeds into a pfte tube that is guided to the ceiling of the enclosure and then drops down vertically to the nextruder. Do you think this setup is problematic?
later edit: since the filament thread is pulled from the bottom/below of the spool, I guess there could be tension in it.
Thank you very much again!
RE: "Nozzle Cleaning Failed." Error
@cupu here is a picture of the printer, where you can see the green filament that is not tensioned between the spool and the Nextruder, it is almost horizontal, so when the Nozzle goes down it could not pull up the Nextruder.
Regards
RE: "Nozzle Cleaning Failed." Error
Thank you @antimix, that makes sense!
RE: "Nozzle Cleaning Failed." Error
Hi again,
In addition to the discussion and good tips above, I've also visited this entry in the KB: https://help.prusa3d.com/article/nozzle-cleaning-failed-mk4-mk3-9_689429
After performing the last step:
"
Temporarily remove the hotend fan by removing the previously adjusted bolts. This will expose the heatsink/loadcell. Then, loosen very slightly the three bolts that hold the heatsink/loadcell in place.
"
I've recalibrated the loadcell and did 2 prints without any cleanup failure at all ; this has never happened before, I used to retry the cleanup process 4+ times before managing a print. It's not a lot of data but I "feel" like things have changed ; as I don't plan on printing anything else soon (if my parts that I just printed fit together) , I thought I'd update here.
Thanks again.
RE:
In case it could be useful to anyone, I use 5kg spools and use some automated system between prints so I need to avoid manually correcting errors so it doesn't negate the automation. The filament tension issue is therefore a problem for me.
So, I modified the start gcode to "tug" on the filament before initiating important operations, to minimise the chances of a failure. Usually does the trick.
Relevant parts:
; Aggressive Z homing
G28 Z ; home Z axis quickly
G1 Z5 F6000 ; move up a bit to ensure it's clear
G28 Z ; home Z axis again to ensure accuracy
G1 Z0 F6000 ; ensure Z is at zero
G28 X Y ; home X and Y axes
; Aggressive tugs to ensure filament is not taut via toolhead movement
G1 Z40 F3000 ; move nozzle to a high position
G1 Z0 F2000 ; move nozzle to a low position quickly to ensure filament tug
&
G92 E0 ; reset extruder position
G1 E15 F300 ; prime the nozzle with a longer extrusion
G1 X250 E60 F600 ; one long purge line at 0.2mm layer height
RE: "Nozzle Cleaning Failed." Error
Having the same issue here with a large spool of filament mounted directly above the printer. Tried adding a tug like @daniel-16 but it doesn't seem to be 100% reliable as sometimes it manages to think it has homed when it hasn't even touched the heatbed... Thinking of solving this with a long PTFE tube to keep the filament length constant when the X/Z axes are moving.