MMu2s MK3S+ Problems with material forwarding  

RE: MMu2s MK3S+ Problems with material forwarding

in my setup,

I use 3x4 mm ptfe so that the filament passes through more easily,
Assuming all the filaments have been loaded in advance, 
when a filament is to be selected,   the filament selector is moved in front of the chosen filament pathway, the Idler roller rotates to line one pressure  rollers up with the appropriate filament path, then the pulley motor rotated to advance the filament, there is an LED on the Finda, that should go out, when the filament passes the Finda, 
the filament should travel relatively quickly down the ptfe towards the extruder, as the filament approaches the Filament Sensor, the extruder motor should start turning, to accept the filament. Once the filament registers on the filament sensor (I have fitted an LED to mine to make it easier to see, the idles should disengage and the  pulley motor should stop turning, and the extruder should be in charge of filament movement,  the extruder should wipe the purge material onto the purge pile, and then when the filament colour has settled, the extruder should continue to the print area. 

at the end of that colour for that layer, the extruder should return to the waste pile (Purge pile)wipe off the nozzle whilst re forming the tip,and then the extruder retracts the filament, once the filament sensor resets, the pulley motor re engages, and pulls the filament out of the extruder, up the feed tube and into the finda sensor assembly, once the finda resets the pully motor pulls the filament out of the selector slider and parks it in the MMU for next use. 

It's possible that the tube between the MMU2 and the extruder is the wrong length, if the extruder is grinding the end of the filament when the pulley motor feeds it down, your  PTFE May be too short, 
and if the pulley motor takes a long time to feed the filament to the extruder the ptfe tube may be too long!   

I started off long, and trimmed a little off at a time, until I got a good length. 

good luck, regards Joan

RE: MMu2s MK3S+ Problems with material forwarding

Are there other error sources for problems with material flow besides the tubing length?

regards

RE: MMu2s MK3S+ Problems with material forwarding

Yes, 
poor preparation of the PTFE  tubes can cause filament to catch on unprepared ends of tubes, or back to front tubes. 

poorly shaped filament ends can cause problems,  this may be due to excess temperature, or inappropriate ramming settings, or insufficient cooling moves.

another issue to be aware of, is... if you get a blockage or similar, you may have to cut the very end of the filament off to remove the immediate issue, BUT, it is worthwhile checking further up the filament, for possible damage to the filament, caused in the extruder bondtech gears,  (grinding a curve into the filament) or in the MMU with the pulleys, grinding a curve into the filament when trying to move the stuck filament... 
either of these damaged areas, may, if not removed, cause a filament out indication, next time the damaged area gets to the filament sensor area... 
It's well worth wasting the length of filament up to the damaged area, instead of getting additional unexpected errors

some people keep the cut off ends, for use with a 3D Pen... where they can be used for free hand modelling, or repair of defects in a print, or for welding together multipart prints. 

I hope this helps, 
Regards Joan

RE: MMu2s MK3S+ Problems with material forwarding

Posted by: @joantabb

 

It's possible that the tube between the MMU2 and the extruder is the wrong length, if the extruder is grinding the end of the filament when the pulley motor feeds it down, your  PTFE May be too short, 
and if the pulley motor takes a long time to feed the filament to the extruder the ptfe tube may be too long!   

I started off long, and trimmed a little off at a time, until I got a good length. 

good luck, regards Joan

You can calibrate the load length for the MMU to the Extruder.

Here is the procedure

https://help.prusa3d.com/guide/service-menu-individual-filament-calibration_86376

RE: MMu2s MK3S+ Problems with material forwarding

My brief experience with the MMU2 have taught me that the position of the filament spools in relation to the buffer is very important. You should be able to easily pull filament through the buffer - if there's much resistance, you need to find another location for the spool. I've tested mine by pushing filament all the way through the MMU2 having the cartridge at a different position than the spool I'm testing. This way I get the filament showing at the MMU, and with the MMU off - not engaging the filament, you need to be able to pull filament relatively easy. In my case I had a lot of spool "run off" meaning the spool would be dragged off the mounts - particular if the spool was mounted a bit high compared to the buffer.

Also, it looks like the MMU has a failure mode when it only progresses filament very slowly. Once it has "success" it will return to feeding it normal speed.

RE: MMu2s MK3S+ Problems with material forwarding

I don't use the Prusa MMU Buffer, instead I mount the rolls on a shelf above the printer
and use two lengths of PTFE to cause the filament to buffer in free space... 

the MMU3 addresses drag within the PTFE Tubes and through the MMU as one of the improvements over the MMU2 

regards Joan

RE: MMu2s MK3S+ Problems with material forwarding

That's a brilliant idea! That pretty much would fit my old setup.  I'm assuming you have a bracket holding in the PTFE on the shelf - do you have extra brackets holding the one that goes into the MMU?

Same size PTFE and all? Definitely need to replicate this setup. And yes, I'm considering the MMU3 but my lazy bum took much too long to get the MMU installed, and once I got started on rebuilding the extruder things did not go as planned and well, many MANY moons later I finally have it running, and now I realize that my experience with it, pretty much fits everyone else's and I should have completely dropped the idea.

Thanks for sharing! I'll get this going ASAP.

Posted by: @joantabb

I don't use the Prusa MMU Buffer, instead I mount the rolls on a shelf above the printer
and use two lengths of PTFE to cause the filament to buffer in free space... 

the MMU3 addresses drag within the PTFE Tubes and through the MMU as one of the improvements over the MMU2 

regards Joan

RE: MMu2s MK3S+ Problems with material forwarding

My spool trays are screwed to the shelf with one screw at the front, and the Short PTFE is drilled through the middle of the spool tray behind the rear roller
this stops the spool holder falling off the shelf or rotating. 
the long feed tubes are free to move, and the correct length to create a smooth curve from the end of the short tubes to the MMU. 
when the extruder is pulling filament, the ends of the PTFE Butt up against each other and allow free flow for the filament, when the MMU Back feeds the filament the short ptfe stops the filament backfeeding onto the spool, which would  otherwise derail the filament and the long tube moves away from the short tube, allowing the filament to coil between the ends of the tubes. 
Nextt ime that filament is neede the mmu first pulls in the free filament then when the ends of the ptfe touch again, it continues to pull filament off the roll

I have nine rolls of filament on my shelf, four for the MMU1 and five for the MMU3.
the mmu1 has 4x3mm  ptfe and I believe the mmu3 has 4x2.5 mm ptfe tubes.

RE:

If you keep getting issues with "fat tips", ie filament tips that show high or very high friction in the tubing between MMU and Extruder, you can buy a PTFE tubing with 2.5 mm inner diameter instead of the default 2.0 mm. I have had no issues arising from that slightly larger inner diameter but at the same time I halso did not have any friction problems due to "fat tips" anymore either. I only have to make sure now that my tips are not stringy but fit tips are now a non-issue. 

EDIT: Does the MMU3 come now wiht 2.5 mm inner diameter by default already?

Or did I initially mess something up by having 2.0 mm inner diamter tubing in place?

RE: MMu2s MK3S+ Problems with material forwarding

Fat tips? Just the opposite - flayed and half extruded ends. I'm getting to be an expert in reloading the MMU2 after cutting the bad/destroyed part of the filament off after prints.

Posted by: @thejiral

If you keep getting issues with "fat tips", ie filament tips that show high or very high friction in the tubing between MMU and Extruder, you can buy a PTFE tubing with 2.5 mm inner diameter instead of the default 2.0 mm. I have had no issues arising from that slightly larger inner diameter but at the same time I halso did not have any friction problems due to "fat tips" anymore either. I only have to make sure now that my tips are not stringy but fit tips are now a non-issue. 

EDIT: Does the MMU3 come now wiht 2.5 mm inner diameter by default already?

Or did I initially mess something up by having 2.0 mm inner diamter tubing in place?

RE: MMu2s MK3S+ Problems with material forwarding

I get both fat tips and a tail on the end. The tail folds back on itself when feeding making it impossible to feed.

I don't get this all the time as I have about a 95% success rate.

I haven't tried the 2.5mm i.d. tubing. Wouldn't I have to replace all but the short piece in the extruder with 2.5mm?

RE: MMu2s MK3S+ Problems with material forwarding

No, you don't have to replace all that tubing, it is enough to replace the one tubing between selector and extruder. That is where you pull the tips back and forth. 
Just check that you don't actually have an 2.5 mm i.d. tubing there already. 

It does not help against stringy tips of course, they are the arch enemy of reliable printing. But it gives you headroom in the settings to avoid stringing as you don't have to worry about that other extreme as much. If you get stringing, make sure your filament is dry. Some brands also work better with the MMU than others. Prusament is a safe bet. I recommend to figure things out with a Prusament PLA roll and when you manage to print without stringy tips, you can try something more challenging. Somewhere hidden in this forum you can find alternative settings for filament change which are much better at preventing strings than the default ones, even though the tips tend to look less perfect. 

RE: MMu2s MK3S+ Problems with material forwarding

Let me describe tonight's MMU "adventure" - talk about becoming an expert in taking things apart and putting it back together.  I have graduately added filament to all 5 feeders - each load takes FOREVER to do, I still haven't found a real good way to do it fast, without breaking/bending the filament in the process - using the provided buffer (it's going to get the boot!). I found a print that used 4 colors and would please my grandson if I could print it. Getting it sliced was quite an adventure as it was created for a different printer and that required to convert part of the format/data to something slightly different than gcode - well, I don't have that and didn't think it should be required. I fixed prusaslicer so it generated "proper" gcode - after about 1 hour of trial and error in the slicer. It finally was able to upload to octoprint and I thought I was about done. But no - I had about 3 hours of more "fixing" to do.

First - let me admit I need to learn about the "tower" for wiping filament when changing colors. It pretty much wanted to use half the print plate for it - a huge waste, and I finally succeeded making it a bit smaller so it would only take 10% of the room. As I hit print "the fun" began. Here's the process I see on the printer: Potential warning I have to acknowledge that the print is for a different printer (seems to happen if the gcode was made for MK3S+ which I thought was the format/model when using the MMU). Next, the printer will heat the extruder and bed, and I swear it takes it longer post upgrade staying at the temperatures "waiting" for things to fall down a few degrees. Mean while the MMU does NOTHING.  Then we do the level calibration (one of my favorite features of the MK3) - still no MMU activity - and then it heads to the first 0,0 point puts the head ALL the way down to the print plate and THEN it tries to load filament.  Well, in this case the MMU "reset" several times, and everything comes to a halt. I find the selector head on the MMU is stuck, some filament didn't restract properly and there's no way to get to it. I couldn't remove the PTFE tube with filament in it going from the MMU to the extruder - only after finding a way to pull the filament from the backside of the printer could I remove the tube, and I found a small piece of filament left from an earlier test print. Removing that, got me to the point where the filament started to go down the PTFE  to stop about 1/3 down, and then retract. This would happen over and over again, even when I forced another filament. A very slow attempt to load and then "reverse". I took the SuperPinda sensor out and rechecked nothing was stuck, and finally I powered down the printer and took the extruder apart (the door with the gear off) and voila I found more filament pieces in there from a previous print.  Now I had to do the sensor calibration and on my printer it's within 1/4 turn of the screw to make it work properly. Takes forever and lots of tweaking to get right.  Then I restarted the attempt again, and this time one of the filaments bend around the filament feeder on the MMU - it was somehow not going through but still being feed through. To get it clear, I had to remove the selector motor, take off the cartridge to remove the filament now stuck inside the selector. It got stuck because trying to pull it out on the back just broke the filament so a piece just long enough to hit the sensor but too short to grab even with the PTFE tube mount off.  Getting that selector off is not fun.

At this point I dropped all ideas of printing - I was more than 2 hours in "fixing the printer/MMU" - I took the printer through filament load, load to extruder, unload manually feed after feed. After having reset the MMU a few times, I finally could load and unload all filament. More so, it was feeding the filament a lot faster than it did before all these issues showed. In the mean time I'd had most tubes dismounted from the back of the MMU so I could pull it out and feed it in for proper loading.  Why? Because somehow the printer puts the bed all the way back, which means it covers the buffer and my access to some of the filament to push it in manually. With the tube's off the MMU I could grab the filament up there and eject/insert it properly. Several times I had to cut the filament to make a clean edge - and then I found the firmware setting to enable automatic cutting - YAY. It even works.

So it worked when there were no little bends, left over "extrusion" on the edge of the filament when it was ejected from the printer. And because "cutting" wasn't on by default, it would insert filament with all kinds of crazy half-melted stuff on it, and some of it would fall off and block the printer.  To make that worse, there's really no error indicate what's causing the error. Ie. if there's a rule in the firmware that the extruder's sensor has to say "no filament" but gcode wants to load new filament, write that error out - write that the printer refuses to load new filament when there's already some present in the extruder.  I wish there was an easier way to get to the filament inside the tubes particular the one going into the extruder - it's very firm when it's loaded with filament, which means helping getting filament out of the extruder is hard. And on the MMU, it feels really odd to have to remove the motor, rotate the threaded rod to get the cartridge off - given the design, it feels wrong that you cannot open the cartridge and easily clear any blockage. And I found the extruder is in the same situation. I had to break my calibration to remove that small piece of filament that had broken off.

Another error that seems to happen a lot is that filament isn't properly pulled back, which means it is still present in the cartridge, not just all the way. This provides enough resistance that the motor will not move - you get the red flashing on one LED or all 5 LEDs and again no error message saying "hey, cartridge is stuck" - you have to look at all possibilities before you find the cause.

By now I can probably assemble the extruder and the MMU by hear. The positive thing is that I got to understand much better how much work post-upgrade so "yay that". But I wasted an evening trying to print a simple 8 layer print with an action figure my grandson loves.

As to the "wipe tower" - so far the few test prints I've done with multi-color seems to have issues with it. From not sticking to getting very rough. Printing the Prusa Whistle with a few color layers looked GREAT until just before the first color change. The last layer done with the first color pretty much destroyed the whistle with what looked like an explosion of plastic on top of it. It was done smooth and to spec until then. And then the wipe tower got the same characteristics, very rough surface as each color filament was added to it. In all my years of 3d printing I've never seen a failure like that. Layer shifts, over/under heating etc. yes - but going from very very smooth printing to a disaster - not talking about underextrusion - it looked like the whistle had exploded and filament was going out of it.

The last comment is that the motor on the MMU responsible for loading the filament into the MMU is constantly hot. Even when no filament change has been done for an hour, it's still warm to the touch as if it's on. I suspect it may be sensing filament use so it uses the motor to calculate the rate - but even if the printer is idle does the motor feel warm to the touch. Either way, I wonder if the feed/forwarding is having an issue. Right now I hope the printer is ready to print "real stuff" because of my last hour of manually testing every aspect of loading, and the whistle print did the filament change correctly - ignoring the mess that was done on the hotplate.

So perhaps this may help others. I've taking these things part to clean them quite a few times over the last week, and somehow I expect that I'll keep having to do that particular if some unexpected error happens - like powerfailures. They're VERY hard to recovery from as the MMU doesn't understand it has filament stuck inside of it, and you cannot just remove the PTFE tube going into the printer so you can pull out the filament. I had to remove the PTFE tubes in the back of the MMU and pull from there which definitely can end up badly if you aren't careful. Before the MMU if filament was stuck I could pull it out once the hotend was at the right temperature, but not with the MMU.  What I have learned is that a failed print can leave "stuff" behind that will prevent the extruder and MMU from working, and it isn't visible from the outside. You have to take things apart to find/correct the error. And with the extruder you then have to calibrate the sensor again. The super PINDA too btw. - the ball will fall out when you remove the cartridge (ask me how I know) but at least it's calibration is easier - hit ball with filament inserted, pull up one click, lock.  I "love" the guide talking about the green light that's on top of the Super PINDA and NOT visible even when I'm standing up by the printer. But there's the support/status screen instead, and I've come to rely on that to see if everything is put back together properly.

So in my case I think the material forwarding issues were caused by "debree" in the unit. The load/unload is a lot faster now than it ever was.

RE:

At the current state I think you shouldn't try to print anything elaborate but stick to MMU calibration prints to trouble shoot your underlying issues. The alarm sign was already when the MMU "reset" during initial filament loading. It shouldn't do that and I am not surprised everything is messed up afterwards. 

I assume you prepared all channels beforehand and loaded filament into the MMU? I always use the cryptic buttons directly on the MMU as that is way more direct. 
After starting the printer, press the right MMU button for a few seconds, that should make the MMU calibrate (move the selector to the right side, hit the side a few times and then back to whatever position). Once that is done you can actually freely move the selector with left and right button (always press for a few seconds). By pressing the central button you can either load a filament into the currently selected channel or, check the currently loaded filament if the MMU can correctly grab it.

If that all works out fine and all filaments are correctly loaded I would pre-heat the nozzle to your filament conditions and then select a filament channel to load into nozzle. Does that work fine? loading issues or motor clicking, clogging etc? Once the filament is loaded subsequently choose to to unload the filament and observe if the filament is correctly unloaded too. Before you start an MMU print, always make sure the filament is actually unloaded. Starting a print when filament is already loaded manually beforehand can mess everything up. 

If all of that works, start a test print (I like the one with the cubes next to each other, you can choose how many channels you want to test, for a start, two colours suffices ), does the start up still causes issues (any reset, no proper initial loading etc), do you encounter any oddities during the print? Remember, any resetting in between a print, if done by the MMU itself or by you, by pressing the recessed reset button is most likely going to mess up your print terminally. At that point you can just as well terminate your print and you need to find the underlying issue. But I would suggest you try out the basic tests I mentioned above to check how deeply rooted your issues are. Unless you have done all of that already, in that case you can ignore my post 😉

RE: MMu2s MK3S+ Problems with material forwarding

Once those basic things work well and calibration cubes work well too, the key for getting successful prints is to tune the MMU with the chosen filament so that the tips are not stringy. The stringiness is also a feature that can take time to build up. So you need to print for at least an hour with lots of colour changes to see if you have an issue with stringy tips at the current combination of settings and filament. Strings create all sorts of problems and mess up everything along the path over time. If you want reliable multicolour printing you need to achieve settings without stringy tips even after longer operation times. 

RE: MMu2s MK3S+ Problems with material forwarding

First thanks for a quick response; I wrote it mostly out of frustrating of what I would consider a wasted evening of 3D printing.

I did leave out a lot though. I absolutely have been using the mystery buttons on the MMU - granted I've used the LEFT button not the RIGHT one to get it to calibrate itself, however it doesn't really help the situation. The MMU will absolutely reset itself and I cannot tell why that happens - all I see is an error on the printer that the MMU failed. It doesn't even fail with all the red LEDs blinking - at least not all the time.  It seem to reset when it cannot push/pull the filament due to the type of blockages I talked about. But there's no way to tell why it fails when it does - which makes it more frustrating.

Using the buttons you cannot load the filament through the selector and into the extruder. Using the buttons it will not grab filament that's been pushed out too far (the MMU has done that too - probably because the filament wasn't cut cleanly after use).  In other words, things seemed to work fine just using the buttons and didn't start failing until the filament had been used by the extruder.

The hidden (to me) options to enable the clean cut of the filament post use most likely the root cause of a lot of my frustration. I'd been removing the filament, cutting it manually, and inserting it again not realizing that a few small pieces had fallen off and blocked extruder and MMU from working.

But regardless, my frustration is not knowing what the failure is and having to disassemble the printer/MMU to just clean out where filament goes - which is brittle and over my many years of printing I've had it break at all kinds of places (lesson learned - cheap filament is not worth the price!). Being able to easily access the channels where filament goes has been a way of life as a 3D-printing hobbyist.

But to your good points - the last test print with the whistle worked after (on the printer) loading to extruder, unloading every filament feed successfully. Seeing the filament come out of the extruder, saying "yes I see the right color" and watching it properly exit (and be cut to a clean edge) by the MMU.  I did this a couple of time with one feed just to test I could reload a filament a second time with no problems. And I found the GCode generated only try to load a filament once - doing exactly what I'd tested with.

As to motor noise - I don't have that, but the MMU is very very noisy particular when it engages to pull filament into the extruder. Clicking sounds that to me sounds like pushing filament too hard are heard as the filament is forwarded into the extruder. On poweron it rumbles LOUDLY as it initializes. Ie. the motors are going to the extreme, finding resistance, the motor is then either released or given a few steps to reverse, and then tries again.  It's the same noise you hear when the MK3 aligns X, Y and Z axis during calibration. But the MMU keeps up the noise much longer than the printer does (3-4 seconds).  Ie. I see this is "normal" - am I wrong?

Thanks again for your feedback. Yes, I'm very new to MMU stuff and I know I'll make more mistakes going forward. I just wish the MMU and the new (to me) extruder design didn't make trouble-shooting/fixing so hard.

RE:

Ok, so the loading of filament into the MMU seems to work fine for you. Good, so we can go to the next steps.

Your issue is further down the line. Does the filament sensor in the extruder work reliably and stably? You can check that somewhere dug in the menu where you can find the sensor values. Open that menu and then trigger the filament sensor manually with a piece of filament, back and forth and also leave it in there for a while. The 0 and 1 should be reacting to your actions accordingly and if filament is in there it should never jump back to zero in between for a short while. If it does that messes the MMUs behaviour in all sorts of ways.

I never ever use the filament cutting, I am not even sure if the blade is even still inserted. It just caused more problems than it did good. If you don't have stringy tips you don't need any cutting and if you have stringy tips, the cutter won't help you against slowly messing up your system anyway.

Never use cheap filament or random filament with an MMU, if you experience trouble. You can get any kind of challenging filament if you like, but only once you have your MMU perfectly dialed in and know that you don't have any MMU related issues anymore. Then you can have fun with tackling filament related issues.

The MMU is not a silent machine but there are various sounds you should be careful about as they indicate issues. If you have repetitive stepper motor clicking there is definitely something wrong. With badly shaped tips, there can be a single sort of click when the filament hits the internal PTFE tube in the extruder (below the extruder gears), that isn't optimal but if not too violent doesn't prevent successful prints usually. However if you have a lot of that, you might damage the top of the tube. If you open the extruder by removing side "door" you can get a glimpse at the top of that PTFE tube. Does the camfer still look neat and nice or is it mutilated in all sorts of ways? If the latter ist he case maybe you want to replace it. That can cause issues during loading and you can't really see it, only hear it.

The rather harsh homing when you the printer on and also when you either press the button the first time or during startup of the print before loading the first filament is normal. It takes a few hits to the wall and all in all a few seconds.

I would recommend to you to go through general trouble shooting, as much as you can without resorting to disassembling the MMU or even doing some mods (other than maybe exchanging the tubing to 2.5 mm i.d.). If you go through all of that and random restarts or shutdowns still persist you might have an electronic issue. There is a whole thread on that here somewhere, it can have something to do with voltage that isn't high enough on the board. I don't have that issue apparently and honestly that is a bit too steep for me too but just that you know if things persist. I wouldn't venture down there right away as long as you haven't checked everything else. Often it is just one or two issues and when you finally resolve them suddenly everything works fine (as long as you evade stringy tips that is ;))

RE: MMu2s MK3S+ Problems with material forwarding

It's how I've been validating/testing the extruder (using the menu). It's very finicly - my own print of the door for the extruder worked, the one I got from Prusa didn't. But I have very little wiggle-room. Ie. a quarter maybe half a turn of the tension screw and it goes to constant 1 (contact) or never showing contact. I've used the trouble shooting guides because initially I kept getting 1 with and without filaments, so I had to figure out what my options where.  I know I need to print more spare "doors" because I do not trust this fragile part (the long arm that goes into the sensor) will stay crispy. Definitely not a fan of that design, but I understand why it's better than some other alternatives.

If I could SEE inside the extruder and/or MMU during operation I would be able to say what is causing the sounds. For now I don't hear/see issues on the extruder once the tension screw is set - I had a lot of noise on the first test after assembling the MMU, but now it's relatively noiseless and no indication that the gears are not grabbing the filament well. First layer prints are very smooth with also indicates a good/calibrated extruder.  My concern is the MMU itself.   And how I've organized the buffer and spools. I know I need to optimize it, and I have seen a great example on this thread of what I can do; even found a great model to mount filament under my shelf that I'll make a test go for and completely avoid the Prusa provided buffer.  I have plenty of PTFE around to test with, particular if the existing tubes fail. If/when that happens I will definitely know where to look for a solution.  Although it sounds like the best solution is the MMU3.

I tend to buy filament in bulk and from known sources.  I learned that lesson many years ago - I've trashed spools where the filament isn't a constant diameter; heck some spools have the filament pulled in a way it gets stuck when you unwind it during printing.  For now I hope to find a quality filament that does NOT come in plastic spools. I have a bunch of empty ones and I either have to make a breakdown/recycle project of those, find a place to donate them to be recycled - and/or just stop using/wasting plastic like that!  But getting 1 or 2KG spools that aren't plastic is a bit scary - not sure paper/carbon will hold. We'll see.

Dumb question - I have a bunch of flexible filaments that I used to print tires for RC models I've created; from what I've read it's not going to be successful on the MMU (haven't tried yet). Can I bypass the MMU completely and just feed it straight into the extruder like I used to do or will the firmware and extruder misbehave this way? From what I did printing spare parts for my enclosure I think I can do that successfully - I'm definitely going to give it a try, but if you have any advice using it WITH the MMU I would definitely like to know.

Thanks again for feedback. A day passed and I'm over my frustration and back to my happy self 😀  I'm still not 100% sold on keeping the MMU but it's definitely working even though it takes a lot more care than the old printing style did. And working is pretty much the key aspect here. So I'm cautiously optimistic - and seeing so many old posts from folks going through the same frustrations and seeing their solutions is making me think I can make it work with the proper setup.

RE:

My recommendation for protecting your own sanity: don‘t use flex materials on a printer with MMU. Some have apparently managed somehow but the MMU really hates flexibles. Some people have installed a mod with a switch that can turn off the MMU, but I have successfully printed with MMU in single colour mode by removing the entire starting g-code except for the heating up. With some dummy first layer object at the bottom. With that change the printer obviously starts printing without filament loaded. I then fully manually guide the flex filament to the extruder until it hits the extruder gears (no menu action, simply by hand) and in the movement menu I then move the extruder forward until som material extrudes and let it flush for a while. It moves very slowly with this option and that is the whole point of doing it that way. Once done I press resume and it prints just fine. I am sure with more g-code skills one could do it more elegantly but my rough method worked for me and isn‘t that much of a hassle.

Regarding the extruder door. I wouldn‘t be worried about durability. If it is working correctly the long arm isn‘t bent by anything, why should it break? It won‘t hurt to have a spare though. If you have a second printer you can simply need a replacement when needed though. I would make sure if I were you that the sensor works spotless. I personally had some real trouble there initially as the tolerances were just a bit too large for reliable signals. What I did after making sure that the sensor itself was fixated well was to print doors with modified sensor arms. I forgot which way I went, either one or two hundred micrometers (maybe more) higher or lower at the end where it hits the light path of the sensor. Just test with which door you get reliable readings without needing to bend anything or something. I did this once and never had any sensor issues ever since.