Load to Nozzle
I am curious on the intended purpose of this function as described in the MMU2 handbook. What I use it for along with the unload filament is not described in the handbook and has undesirable effect and am wondering if this is normal or should not be used for the purpose I am about to describe.
I use the MMU2S with up to to 5 different color or types of filaments loaded. When I slice a single colored object, I select the extruder number correlating to the color or type of filament I have loaded. If the previous print was in a different color or type, I want to purge the nozzle of that color/type previously used with the filament I will be using. It seems logical for me to preheat, and load to nozzle the intended filament I plan to use. This allows me to purge until the I feel the color is correct or the filament material is completely homogeneous. Keeping in mind now, I have sliced the ready to print model under the MMU2 profile and not the single MMU2 or non-MMU2 profile. If I do not unload the filament before I select "print" the hotend tries to print the beginnings of a purge line like it was a printer without an MMU, like a high flow rate with next to no nozzle to bed gap and extruder sounding like it's grinding the filament, then proceeds to lay out the longer purge line like it would normally with MMU coding.
I usually unload filament prior to selecting "print" so the print initiates properly and avoid this high initial flow blobbed purge, but forget sometimes and I get the above results. However, when I do unload, it appears the filament will not go through the proper cooling moves to produce a good tip, and I hear grinding noise from the MMU as it tries to pull back the filament. The tip looks okay sometimes, and it seems like the extruder is not releasing the filament before the MMU pulls on it, at least some of the time.
Is my use of the load to nozzle not a good work flow for setting up the purge of a different filament? I am curious what others are doing to adequately purging filament color/type in this setup.
RE: Load to Nozzle
Just a little help as we are STILL trying to get it to work for us but any way change the color in the slicer program not from the printer it will purge on the front of your bed before it starts the printing. We also had a problem when changing colors and we found out that the F.I.N.D.A was showing a 1 even if there wasn't any filament loaded. We looked closer and found a piece of filament stuck at the FINDA. Also had to re-calibrate the FINDA. It is getting better but if we stop a print because of a bad first later then decide to print something else with a different color it stays at the first print color. Going to have to check the FINDA again. Not sure if any of this is your problem?
RE: Load to Nozzle
The one problem you mention, I experience as well is during a single color print, if first layer is bad, or the print just needs to be aborted, I find the MMU2 unloads better if you pause first, then stop print. When stopping without pause, the MMU2 seems to want to rip the filament out of the extruder via grinding noise and without cooling moves. I have had no issues with color change after a stopped print, but may not have noticed it. I do notice though after a stopped print, the menu does not default back to normal where I can select a pre-heat. If I pull out the SD card and re-insert, I can get the default menu back. What you described is not the workflow I am wondering about but I share the same issues you do.
I think there are some refinements to the MMU2 firmware and slicer coding that need to be looked at from the developers. It definitely could be better.
RE: Load to Nozzle
Have you ran into the problem of the filament getting to dry and snaps off?
RE: Load to Nozzle
Yes, when I have the filament sitting in the RMU, it does break, but not because it's dry. I believe the RMU spool radius is too small and stressing out the filament over time. I am running TNDave's buffer which has the larger radius with much better results.