RE: MMU2s Single Unload Fails
@steve-e3,
Thank you again for continuing to help me with this issue. I have really enjoyed the discussion.
To close out our philosophical conversation regarding the MMU, your points above have caused an immediate shift in my thinking. Like you, I delayed installing the MMU for a significant period of time (I estimate close to a year) while I made sure that I had the base MK3S operating perfectly and had developed a firm foundation of 3D printing knowledge and proficiency. It never even occurred to me to go back and reprint updated parts. Thank you for this advice. This would have probably prevented my shift to the alternate selector block. That said, I'm sticking to my guns on the rear ptfe holder. The festo fittings allow me to easily shift between direct feed for single color prints and the buffer for multi-color prints. I have read your other posts, so I am not even going to tell you that I run without a buffer for two and three colors and never (knock on wood) have problems. 🙂 I truly believe in complexity reduction whenever possible.
Picture attached. This shape is representative of the vast majority of instances.
Yes, my problem is only with PLA and I agree that this is one of the two biggest clues. The other is that my PLA tips are perfect in multi material mode. This caused me to discount nozzle (yes, changed) and ptfe (yes, changed, not deformed in any way, inserted correctly).
All this said, I have contaminated my science project. As I mentioned in one of my previous posts, I stripped the aluminum threads in the heater block (my lesson learned is that the proper torque spec is 2.5 Nm and all future installations will follow the practice of the Prusa engineers and use a torque wrench). This caused me to change many of the components potentially impacting the root cause at one time.
I am going to continue to monitor the printer and focus my efforts now on the slicer as you suggest.
Again, thank you.
RE: MMU2s Single Unload Fails
@tg73
Thank you! Understand and agree with all.
RE: MMU2s Single Unload Fails
Okay I promise this is my last MMU/mod comment but regarding "The festo fittings allow me to easily shift between direct feed for single color prints and the buffer for multi-color prints", I use the MMU for both including single filament printing. Works perfect. No changes needed.
Just for clarification, when you added the new MK3s + MMU2s to your list of available printers in Prusaslicer, you will now have 3 MK3 printers, with 2 potentially for single filament, the two being:
- Your original MK3s (pre-MMU2s) which is no longer needed.
- The new MK3s Single Filament (post-MMU2s)
(And of course in addition to the above you now have the MK3s Multi Filament (again post-MMU2s)). When you say you print in single-filament, which printer profile are you selecting? (I am guessing the old original profile, not the new one since it sounds like you are re-configuring to avoid using the MMU. If so have you tested with the new single profile with it passing through the MMU?)
When you say you stripped the threads in the heater block, there are 2 sets of threads: one for the nozzle, and one that clamps the heater element. I am assuming you are referring to the latter. BTW the thermistor is on the opposite end - I wonder if for PLA-temps the clamping or heat flow is somehow different because the clamp may not be working? (E.g. more thermal expansion at the much higher PETG temps clamps the heater better, etc. And yes I realize theoretically it shouldn't matter because of what the thermistor registers).
However looking at your tip, sheesh it sure seems like somehow there is a tiny blob of solidified PETG stuck in there somewhere causing it to deform just a bit when the PLA is extracted. Your tip is near perfect. It has the characteristic slightly enlarged diameter at the top (spool end), it has the conical shape as you approach the tip, looks about the right length where the tip should end, but then has an attached blob.
Gosh it seems like if there was residual PETG in the nozzle, or if the PTFE was not all the way down to the heat break and then some PETG went back up the heat break and into the gap that it would affect tip shape during PLA but not during PETG.
FYI, I dont think I mentioned this on this thread but if I did apologies for the duplication, I did have a weird Prusament PETG blob happen to me. I do mostly PLA and infrequently PETG, however I did a lot of PETG recently. After several successful PETG prints I started another and I was actually watching it putting down the first layer when the filament stopped coming out for about 3-4 seconds, and then like a dam bursting a blob blurted out with some force. My subsequent prints had blobbing issues during first layer. In all my years of printing this was the first time where I consistently could not put down the first layer so it was pretty concerning.
Soooo....thinking about it, and with it looking like the nozzle was physically plugging I took one of those nozzle-cleaner needles and with the nozzle heated to 240c I stuck it up inside the nozzle (angling it around) and was surprised. Even at 240c it felt too thick and viscous, and as I worked the needle in and out the filament solidified to the cooler needle and I was able to slowly draw filament out (wiping the needle free of the coating of PETG each time). After spending some time doing this I then manually moved the E-axis to extrude filament, and when I put the needle back into the nozzle the molten filament (there's nominally about 50mm**3 in the nozzle) seemed to have normal viscosity. I then re-started my long print printing entirely at 250c (10 above what Prusa defaults to) and my prints were absolutely perfect. I then switched back to 240c and again my subsequent prints were perfect.
Unfortunately I don't know exactly what happened. In my mind's eye there was some "bad" PETG buildup in the nozzle that maybe was soft but not fluid enough to come out and that created a blockage and that I eventually drew out with the needle. When I subsequently changed to PLA I loaded it at 240 (thinking this keeps the residual PETG that is in the nozzle fluid), manually moved the E-axis to extrude, then retract slightly, then extrude quite a bit of the PLA and then lowered it to 215 and manually extruded even more in an effort to "flush out" as much of the residual PETG as possible. (I haven't had any issues since then (knock on wood)). If there was a blob of "bad" PETG along the inside of the nozzle...if in fact this has any truth to what happened to me, then it would certainly affect the shape of the tip during PLA removal, making it asymmetrical perhaps even into a bend. Just a long-winded thought given my experience.
Keep us updated.
RE: MMU2s Single Unload Fails
You know I would be tempted to open the panel to disengage the bondtech gears, remove the festo fitting from the extruder on top, heat the nozzle and just manually feed PLA (no extruder) and manually retract it by hand and see how if feels and what shape you get.
RE: MMU2s Single Unload Fails
@steve-e3,
I am not saying that I bypass the MMU for single color prints. I am saying that I bypass the buffer for single color prints. I included a picture with one of my previous posts if you are interested in my arrangement. This is how I run single color.
I started with a fresh install of PrusaSlicer after adding the MMU. The only profiles in my slicer are for MMU2S and MMU2S single filament.
Your assumption regarding which threads I stripped is incorrect. I stripped the nozzle threads.
I appreciate your perspective and agree that the root cause could potentially be residual PETG. I will try a cold pull as others have suggested and maybe some of the actions you took to clear your blob. In your post, you mention manually moving the E-axis. How do you do this?
RE: MMU2s Single Unload Fails
@steve-e3
Regarding manually feeding filament into the top of the extruder - I have done that and the tips look good. I wonder if the curve in the tip is being shaped by the bondtech gear itself. This is the only component that is curved in that portion of the filament path.
RE: MMU2s Single Unload Fails
"In your post, you mention manually moving the E-axis. How do you do this?"
Settings/Move Axis/Extruder.
I think its indiscriminate so make sure your nozzle is heated.
RE: MMU2s Single Unload Fails
I thought it may be useful to upload a pic of my filament tip for reference. This is a typically shaped tip after retraction on my machine using all default settings in the slicer as well as the printer. The filament is PETG in this case however PLA looks identical.
RE: MMU2s Single Unload Fails
Good News: One last update to this thread because my PLA unload fails seem to have stopped.
Bad News: I was not able to isolate the issue to a single root cause.
As discussed above, I had to replace my heater block because I stripped the nozzle threads during a momentary loss of good judgement and procedural compliance. I needed the part quickly so I chose to order and install the E3D hotend kit from Amazon ( https://www.amazon.com/gp/product/B07YNHS6F4/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1 ) which was delivered next day (on a Sunday).
After changing the hotend, my problem went away for both printer driven unloads (first layer cals, print cancels, etc.) and gcode driven unloads. Filament tips look perfect in both cases.
Here is the product description, which is very interesting:
"The Prusa specific iteration of the V6 HotEnd - intended as a drop-in replacement for your original Prusa i3 MK3 or MK3S printer. Ships with the standard V6 components, plus a Prusa specific thermistor, heatbreak and 40W heater cartridge. The Prusa V6 HotEnd offers the same all-metal, high-performance reliability of the V6, whilst swapping out several of our standard components with Prusa specific parts. These include a 40W heater cartridge for increased power, a longer wired thermistor and a heatbreak with Prusa specific internal geometries - designed to improve retractions with the Multi-Material upgrade. This is a 24V HotEnd and is intended for function with a Prusa MK3 or MK3S. Do not use this HotEnd with 12V Prusas such as the MK2 or MK2S as this may damage your printer. Please note - this HotEnd does not come with the specific PTFE used by Prusa, please retain the PTFE from your existing HotEnd. For reference, PTFE should look like this on the MK3S/MK2.5S and this on a MK3/MK2.5 MMU2."
Most notable "heatbreak with Prusa specific internal geometries - designed to improve retractions with the Multi-Material upgrade." No idea what this means and if the hotend internal geometries are different than the one that came with my MK3S.
I have no idea whether problem resolution was due to a some change in hotend component design or just simply a result of changing all the components that came in the kit.
RE: MMU2s Single Unload Fails
@john-w80
Well, first of all congratulations and what a relief it must be to have everything working properly!
When you clarified that you stripped the nozzle threads in the heater block that quite honestly was an "ah-ha" moment for me; if stripped, there is enough positive and negative pressure in the nozzle to potentially cause "wiggle room" -- only the slightest amount is necessary -- to cause filament end issues. I have been conversing with someone on another thread that had done the exact same thing and caused similar issues. I suspect that this was the root cause of your issues although the proof is left to the reader. (I hope it has become obvious why I start any dialogue in helping someone with questions about modifications or anything that is out of nominal; not to be a PITA but it's simply these changes or deviations that cause issues. We all start with perfectly working Prusa machines and diverge from there...).
I'm not sure "heatbreak with Prusa specific internal geometries - designed to improve retractions with the Multi-Material upgrade" is anything more than the standard Prusa heatbreak....my setup is a MK3 upgraded to an MK3s, meaning specifically it was my original heatbreak from years ago recycled and re-inserted into a newly designed hotend. Again I believe your stripped threads on your heater block for the nozzle is my guess for the main culprit.
Either way glad your up and running and can mark this thread as resolved!
RE: MMU2s Single Unload Fails
I came here looking for help with this same problem. I followed the link above that contained an end GCODE to help with ramming issues and it seems to be working for me. I merged it with the default GCODE. Hope this can help someone who was as frustrated as I was with single color printing through the MMU2.
{if max_layer_z < max_print_height}G1 Z{z_offset+min(max_layer_z+10, max_print_height)}{endif} F720 ; Move print head up
; Filament-specific end gcode
M83 ; extruder relative mode
G92 E0 ; reset extrusion distance
G1 X0 Y210 F7200
; CP TOOLCHANGE UNLOAD
G1 F1600
G1 E0.3085
G1 F1687
G1 E0.3252
G1 F2261
G1 E0.4359
G1 F2904
G1 E0.5599
G1 E-15.0000 F9000
G1 E-24.5000 F5400
G1 E-7.0000 F2700
G1 E-3.5000 F1620
G1 E20.0000 F267
G1 E-20.0000 F283
G1 E20.0000 F299
G1 E-20.0000 F316
G1 E20.0000 F332
G1 E-20.0000 F348
G1 E20.0000 F364
G1 E-20.0000 F380
G1 E20.0000 F397
G1 E-20.0000 F413
G1 E-35.0000 F2000
M140 S0 ; turn off heatbed
M107 ; turn off fan
M702 C
G4 ; wait
M221 S100 ; reset flow
M900 K0 ; reset LA
{if print_settings_id=~/.*(DETAIL @MK3|QUALITY @MK3|@0.25 nozzle MK3).*/}M907 E538 ; reset extruder motor current{endif}
M104 S0 ; turn off temperature
M84 ; disable motors