Pre-unload Extrude to Form Smaller Filament Tip, A New Option in Kuo Firmware
Advancing the extruder a little bit (5mm) before unloading filament results in a nicer tip. Here is the resultant PETG Prusament tip with that option is enabled in my firmware branch. https://github.com/guykuo/Prusa-Firmware/tree/0.9-Degree-Stepper-Support
The option is turned on by default. You can turn it on/off by commenting in/out one declare in configuration_Prusa.h
//====== Kuo extrude before unload filament
#define EXTRUDE_BEFORE_UNLOAD //uncomment to always extrude filament a short distance before unloading. Forms smaller tip.
Click image for larger view. Filament tip is much easier to pull out of extruder and can be reinserted easily. Very stringy filaments will still form a string, but remainder of tip should be well formed.
This has not been checked for MMU2S compatibility. If it is problematic with MMU2S, comment out the define to disable the extrude motion.
RE: Pre-unload Extrude to Form Smaller Filament Tip, A New Option in Kuo Firmware
Advancing the extruder a little bit (5mm) before unloading filament results in a nicer tip. Here is the resultant PETG Prusament tip with that option is enabled in my firmware branch. https://github.com/guykuo/Prusa-Firmware/tree/0.9-Degree-Stepper-Support
The option is turned on by default. You can turn it on/off by commenting in/out one declare in configuration_Prusa.h
//====== Kuo extrude before unload filament
#define EXTRUDE_BEFORE_UNLOAD //uncomment to always extrude filament a short distance before unloading. Forms smaller tip.
Click image for larger view. Filament tip is much easier to pull out of extruder and can be reinserted easily. Very stringy filaments will still form a string, but remainder of tip should be well formed.
This has not been checked for MMU2S compatibility. If it is problematic with MMU2S, comment out the define to disable the extrude motion.
MMU does not use built-in single-mode unload routines and should not be affected since it has its own ramming sequence defined by the filament itself.
RE: Pre-unload Extrude to Form Smaller Filament Tip, A New Option in Kuo Firmware
MMU does not use built-in single-mode unload routines and should not be affected since it has its own ramming sequence defined by the filament itself.
That is good to know. The next experiment will be reduction of stringing on the super stringy filaments. I think it can be done with a sequence like
1. Extrude 5 mm
2. Fast retract 10 mm (create SHORT initial string)
3. Slow speed advance 9 mm (shorter move to remelt/ shorten initial string leaving smaller pedicle to break)
4. Fast retract 50 mm to break smaller pedicle and hopefully yield a smaller string.
5. Complete medium speed unload
The trick will be getting the initial string to melt without creating a pool above the melt zone. I think the initial string should be still straight enough to drive into the melt zone if I keep it short enough. Too long and it will pool. Too short and it won't be any smaller a pedicle.
RE: Pre-unload Extrude to Form Smaller Filament Tip, A New Option in Kuo Firmware
I had an initial thought that it might be neat to use the filament's MMU ramming settings to do the unload even for single filament mode (it's not hard to generate the g-code sequence for it; I've done so in my bucket-mod processing scripts). But the gotcha here is that the question is "what filament" and that alas, in many cases shy of an M600 mid-print, there's no context as to what the currently loaded filament is, making that very impractical.
RE: Pre-unload Extrude to Form Smaller Filament Tip, A New Option in Kuo Firmware
The MMU2S ramming sequence - where is the filament tip moving between during the sequence? My understanding was it is at the Bondtech gears were used to do the forming. I'm planning to do the forming at top of the melt zone. The planned sequence should only affect filaments that form strings, but do nothing to those not stringing.
RE: Pre-unload Extrude to Form Smaller Filament Tip, A New Option in Kuo Firmware
No, it's also done in the PTFE.
There's a ram, followed by a high-speed retract, and then the filament is dipped up and down in the heatsink PTFE to form it ("Cooling moves"). This is why hot-end PTFE is critical to good MMU reliability; if you use oversized/cheap stuff it gives fatter tips that cause no end of load issues later. (ask me how I know...)
Then finally it's retracted to above the bondtech gears where it's handed off to the MMU2.
Have a look at the generate_toolchange function in
https://gitlab.com/gnat.org/originalprusa/blob/master/devices/mmu2/bucket/tool/bucketrandom.py
for some details/insight on the sequence of events, let me know if there's anything I can explain further.
RE: Pre-unload Extrude to Form Smaller Filament Tip, A New Option in Kuo Firmware
I appreciate the documentation found in your firmware branch.
I finally got my Arduino libraries updated for the Prusa MK3.