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Mathieu
(@mathieu)
Active Member
Successful MMU2S Modifications (re-upload)

Hi there! I'm Mathieu. This was supposed to be posted earlier but I pressed the Enter button too early by accident and uploaded an incomplete thread that didn't have all I had to say. Last time someone notified me that I sounded a little snarky about people's attempted solutions to the MMU2 and that was not my intention, so I'll try to reword a little bit this time. So, this might be a little redundant at first but I have some good news!

I am the lone reviewer of the MMU2S on the Prusa e-shop website, with 3 stars. I was in a bad mood that day but I rated it high because the actual structural integrity and concept of the upgrade was great but the actual use and learning curve was difficult to master. However, I can gladly say that, for the first time in over 6 months of owning the MMU2, I have finally gotten my first print with no jams, layer skips, or user intervention! In fact, not just one print, but four! With a combined layer change count of nearly 1000 I will show some physical and in-slicer tips that will get you on your way to MMU enlightenment.

Many people have set off to find the elusive flawless MMU settings that have escaped our grasps since the beginning of time. Sadly, the results I am posting are not guaranteed for all, as I understand that not everyone lives in the exact temperature and humidity as I do. That would be nice, though! Without the hardworking community working together to share the best ways to cope with the finnicky MMU2 I would not be writing these posts. So, here's a list of three links to important modifications that miraculously stopped my prints from failing. I'm sure there are more that can do the job just as well but these are the only ones I used.

https://www.prusaprinters.org/prints/1829 (better MMU selector with wider filament holes = more tip tolerance)

https://www.prusaprinters.org/prints/3417 (slightly changed extruder idler door) I'm not sure if this one is nearly as important but it works.

https://www.prusaprinters.org/prints/3676 (this one is BY FAR the most important. It uses a pass-through coupling to feed filament through the PTFE tube right up to the Bondtech gears)

The last of these models uses a redesigned extruder body to allow for a pass-through coupling that bypasses any resistance a filament tip would encounter by the stock (default) extruder body. This was the deciding factor that really helped me the most. You might have to buy a new PTFE tube for this purpose but the ones on the Prusa e-shop work just fine! If you are buying from somewhere else, the creator says to use a 3mm ID 4mm OD tube but I think having an inner diameter of 2mm works just as well or better, having better accuracy when the filament is exiting the tube on the other side. The creator kindly left a link to a set of pass-through couplings on Amazon (USA) that I bought and have used. You only need 1 and the regular Festo stays on the MMU end. The mod is complete with a window to view the Bondtech gears do their magic (or not do what they're supposed to do, but hopefully not).

My pass-through setup. I have a ziptie under the black collar of the coupling to keep it in place.

There are two other physical problems that I had to solve and one was easily solved by the pass-through coupling modification. The first was about load timing. When the filament successfully makes its way down the long PTFE tube from the MMU unit to the extruder there are two options, from what I've seen: the successful option is when the printer pauses for half of a second and then continues to push the filament down to the hotend, and the unsuccessful option is when there is no pause, causing the filament to jam, strip, and attempt to reload again (for some reason it almost always works the second time despite nothing changing). This is heavily-dependent on the IR sensor's location, but after disassembling the entire MK3S extruder to install the pass-through coupling mod and randomly putting the IR sensor in place, I have not had this issue ever since. With the normal-length PTFE tube provided by Prusa with the default extruder setup, the unsuccessful option happened to me a lot. I'm not sure if anyone else has had this problem (I'm sure people have had problems with jams but I don't know if it's in the same way as I'm trying to describe). However, even when using the same length of tube as before, the pass-through coupling modification decreased the time it takes for the filament to get to the Bondtech gears so the printer had to take a pause because the filament reached the Bondtech gears earlier than expected. This is key in preventing the "zero wait" jams that I had had since I upgraded to the MMU2S.

The second physical issue was about the tip size. Of course, the end of the tip, stringy, bulbous, or otherwise, greatly depends on the filament but the creator of the pass-through coupling modification claims it can feed any tip. The thing is, it's not so much the shape of the tip that matters but rather the width. The number 1 factor for a filament load jam (from what I've seen) is when the filament tip is shaped in a way so that it can't enter the extruder's PTFE tube; it's too wide, gets stuck, and gets stripped by the Bondtechs. Make sure that you are using the updated MMU2S PTFE tube that Prusa has. It is the perfect length and has a perfect inner diameter that is much closer to 2mm than 3mm (the one I got when I upgraded to the MMU2 in November 2018 was much wider on the inside and was too long). This is important because it shapes filament tips in a way so that the tip width is almost exactly the same as the normal filament, reducing the chance for fails. The inner diameter of the long PTFE tube doesn't really affect the problem but definitely consider checking to see if you have the right PTFE tube.

Of course every picture I take is blurry when I need detail (facepalm). However, without changing any PrusaSlicer settings, I repeated the same print and got a much thinner and much more tolerable filament tip (the top one in the picture). This is key for preventing jams. In combination with the pass-through coupling mod I have never had a filament jam.

Now, here's the tricky part: the slicer settings. Since I got the MMU2 upgrade in November 2018 I have seen countless YouTube videos about slicer settings that you need to get it juuust right. I didn't succeed with them, but that's not the fault of whoever found the settings, because it worked for them but not for me. My belief is that the biggest problem for me in particular is that thick ends of filament after the unload get caught when they are loaded later on during a print. If the filament tip is too big upon reinsertion, it will get jammed and you will have an unhappy printer and a headache. Below I am sharing a list of changes to the stock "Prusament PLA MMU2" settings in PrusaSlicer, which have been accomodated specifically to work with any Prusament PLA but have worked for other brands such as 3D Solutech and Filamentum. Everything under "filament settings" is the same as normal except under "Advanced", where the changed settings are below:

Loading speed: 21 mm/s

Unloading speed at the start: 125 mm/s

Number of cooling moves: 3 (I will elaborate on this in a bit)

under Ramming settings, the total ramming time is 3.50 seconds.

 

Everything else is the same as the generic Prusament PLA MMU2 settings. Much of my reasoning for these changes are from other users here, saying that increasing the load speed is beneficial for the start of a filament load. I increased the initial loading speed from 100 to 125 because the increased speed, as I've seen, greatly decreases the stringing on each filament tip as it unloads; most people use 120 instead of my 125 but anywhere between 120-140 should yield better results without having long-term effects on the extruder motor (I'm pretty sure using 200 mm/s would have some negative effect). Many people say that a higher amount of cooling moves results in a thinner point/tip but I have not seen a major correlation. Using 2 or 3 filament moves, as I've seen, yields similar results but I use 3 just in case; 4 and beyond is just not worth the time it adds. From a few YouTube videos from people who got the MMU2 early, they say that increasing ramming time until there is a spike in the rammed volume (you'll be able to tell from the graph) is important because it irons out the bulbous end of the filament. I would recommend using a ramming time of rather 3.5 or 4 seconds.

Those are all my tips for now! I really hope this helps as I understand it is definitely annoying to get the MMU2 to work and I still don't know how Prusa got all those prints so easily. Best of luck!

Mathieu

Hi! I'm Mathieu!
Thingiverse: https://www.thingiverse.com/BramForReal/about
YouTube: https://www.youtube.com/channel/UCh-2bXtfv-nLwgwO7H7IJxA
I have an Original Prusa i3 MK3 with MMU 2.0. Nice meeting ya! :D...
Posted : 23/06/2019 3:10 am
JSmith, CybrSage and gnat liked
CybrSage
(@cybrsage)
Honorable Member
RE: Successful MMU2S Modifications (re-upload)

I have been collecting thingiverse items that have helped me, though admittedly it is still a work in process (slowly testing one change at a time).  

https://www.thingiverse.com/cybrsage/collections/mmu2-mods

Posted : 26/06/2019 2:28 am
MikiCab
(@mikicab)
Estimable Member
RE: Successful MMU2S Modifications (re-upload)

I am getting tired of all these upgrades to get this thing to work.  I got one set of successful prints so far.

Posted : 07/07/2019 9:20 pm
Thunderhead
(@thunderhead)
Active Member
RE: Successful MMU2S Modifications (re-upload)

@makermathieu, I think that you're the lone reviewer of the MMU2S on the store because they've disabled the submit button because this is essentially a failed product.  The store title should reflect the alpha nature of this product.  IE:  Don't buy this unless you've got tons of time and patience to print new parts and mess around with settings.

To add to @mikicab's post above, how could Josef Prusa release such an amazing piece of garbage after designing such a wonderful printer? It baffles the mind. Maybe that's why the Prusa name doesn't appear anywhere on the MMU2S?

Before the 'upgrade', the Prusa MK3S printer was a reliable workhorse that could be counted on to finish prints overnight with a very low frustration level. We loved it and used it all the time... we had jobs queued to run so that there was never a moment of available print time wasted.

After the installation and tuning of the MMU2S, my beloved MK3S has turned into the most frustrating piece of equipment in my shop. It's actually become something of a running joke in my shop: "How far can we get into a print before the MMU2S screws up and causes us to waste another batch of filament?"

I've put 60+ hours into tuning and troubleshooting the MMU2S and I'm ready to pitch the whole thing into the trash can! In fact, I'd like a refund.

If you're reading this prior to purchasing an MMU2S, do yourself a favour and pass on this 'upgrade' and wait for a real solution to multi-material printing from Prusa.

Posted : 08/07/2019 5:49 pm
ssill2 and rmorgansd liked
CybrSage
(@cybrsage)
Honorable Member
RE: Successful MMU2S Modifications (re-upload)

Hyperbole does not help anything, but it often causes others to ignore the complaint.

Posted : 08/07/2019 5:57 pm
JSmith and gnat liked
Thunderhead
(@thunderhead)
Active Member
RE: Successful MMU2S Modifications (re-upload)
Posted by: CybrSage

Hyperbole does not help anything, but it often causes others to ignore the complaint.

Perhaps my frustration level is overriding my hyperbole detection.  Or maybe it's the garbage can filled with wasted prints and filament.  Hard to say at this point.

Posted : 08/07/2019 6:14 pm
CybrSage
(@cybrsage)
Honorable Member
RE: Successful MMU2S Modifications (re-upload)
Posted by: Thunderhead
Posted by: CybrSage

Hyperbole does not help anything, but it often causes others to ignore the complaint.

Perhaps my frustration level is overriding my hyperbole detection...

This is almost always the case.

Posted : 08/07/2019 6:30 pm
gnat
 gnat
(@gnat)
Noble Member
RE: Successful MMU2S Modifications (re-upload)
Posted by: MikiCab

I am getting tired of all these upgrades to get this thing to work.  I got one set of successful prints so far.

Actually no modifications (beyond possibly dealing with a misprinted part) are required. 

Anytime one of us makes a modification it is because we are trying to address our configuration not being that which was designed/tested. The reasons for those differences are irrelevant though as all that matters to us is getting it to work. 

The first step in that process, however, is to understand how the whole system works so that you can identify where your particular issues are. If you don't get that first step, then you will just be blindly throwing solutions at the problem and many never find the answer. 

The thing you have to remember (and tolerance for such is where I think Prusa needs to improve) is that every configuration is different. This means that what works for me is not likely to work for you without adjustments. It also means that there isn't likely to be one thing that fixes it and it will instead be a combination of things. 

This is by no means a perfect product and there are plenty of things for Prusa to improve, but for this point in it's development it is actually pretty solid. 

MMU tips and troubleshooting
Stop SL1 tank leaks with a simple o-ring...
Posted : 09/07/2019 1:31 pm
gnat
 gnat
(@gnat)
Noble Member
RE: Successful MMU2S Modifications (re-upload)
Posted by: Thunderhead
Posted by: CybrSage

Hyperbole does not help anything, but it often causes others to ignore the complaint.

Perhaps my frustration level is overriding my hyperbole detection.  Or maybe it's the garbage can filled with wasted prints and filament.  Hard to say at this point.

How about comparing it to the current i3 printers for starters? Not only is that an unfair comparison, it's inaccurate too. The MMU is a much younger product with far less time in development and in user hands. The i3 was no walk in the park at this stage of its life either. 

What is clear, however, is that Prusa is working on it and improving the design. I have little doubt that it will be as user friendly as the MK3S in time, but in the mean time people that want to play with it now have to understand and accept that they are playing with something new.

MMU tips and troubleshooting
Stop SL1 tank leaks with a simple o-ring...
Posted : 09/07/2019 1:36 pm
CybrSage and JSmith liked
Mathieu
(@mathieu)
Active Member
Topic starter answered:
RE: Successful MMU2S Modifications (re-upload)

I just looked at this for the first time since posting this thread. And, I would have to agree. The MMU2, although I don't hold it in as low of a regard as you do, is indeed not a creation that I would see Prusa showing off with pride. Like I mentioned in the post the hardware is pretty solid, but the design is slightly flawed and the main problem is just that no matter what settings you use the tip will always be different for everyone. Even the settings I posted here, even though I have still not gotten a print failure, often still results in stringy filament tips. I worked late on school nights (a little younger than I picture most users here are) to troubleshoot the MMU2 (before they added the S which saved me much time), often just sitting in my chair in awe at how such a successful printer like the MK3 could have such an evil twin.

I understand it is very, very hard to stay positive about issues with the MMU's, and my post is only so cheery because shortly before posting it I had a "boo-yah, in your face!" moment upon installing the hardware modifications.

I'm not sure what issues you might be having but I guess the $300 wasted on the MMU2 can give you easy access to having 5 colors on demand instead of 1, even if that's the only thing the MMU2 can do.

I wish you the best in your forever troubleshooting, and hey, if all else fails, just take it off and you have a perfectly capable MK3(S)!
Mathieu

EDIT: I thought this would show up as a direct reply, but it didn't. This was meant for @Thunderhead.

This post was modified 2 years ago by Mathieu
Hi! I'm Mathieu!
Thingiverse: https://www.thingiverse.com/BramForReal/about
YouTube: https://www.youtube.com/channel/UCh-2bXtfv-nLwgwO7H7IJxA
I have an Original Prusa i3 MK3 with MMU 2.0. Nice meeting ya! :D...
Posted : 11/07/2019 9:31 pm
CybrSage liked
shilbert
(@shilbert)
Active Member
RE: Successful MMU2S Modifications (re-upload)
Posted by: MakerMathieu

Many people have set off to find the elusive flawless MMU settings that have escaped our grasps since the beginning of time. Sadly, the results I am posting are not guaranteed for all, as I understand that not everyone lives in the exact temperature and humidity as I do. That would be nice, though! Without the hardworking community working together to share the best ways to cope with the finnicky MMU2 I would not be writing these posts. So, here's a list of three links to important modifications that miraculously stopped my prints from failing. I'm sure there are more that can do the job just as well but these are the only ones I used.

https://www.prusaprinters.org/prints/1829 (better MMU selector with wider filament holes = more tip tolerance)

https://www.prusaprinters.org/prints/3417 (slightly changed extruder idler door) I'm not sure if this one is nearly as important but it works.

https://www.prusaprinters.org/prints/3676 (this one is BY FAR the most important. It uses a pass-through coupling to feed filament through the PTFE tube right up to the Bondtech gears)

Mathieu

I read this post over and over and should have gone for the better MMU selector and changed idler door immediately. In the end I did not have to go for the pass-through coupling nor exchanged ptfe tubing.

I did experience hours of unloading and loading (to the extruder) problems but that went away with the exchanged selector.

Very likely the Universal Auto-Rewind Spool Holder also helped.

After a 2,5h two color print with 2 MMU load failures (no manual interaction) I have started a 1d18h print now 🙂

One last thing. My ramming settings are different from what is described above. Differences from Prusa PLA settings:

Loading speed : 22

Unloading speed at start: 80

Cooling moves: 2

Speed of first cooling move: 2

Speed of last cooling move: 1

Ramming settings

This post was modified 2 years ago 2 times by shilbert
Posted : 29/07/2019 8:27 am
CybrSage and liked
CybrSage
(@cybrsage)
Honorable Member
RE: Successful MMU2S Modifications (re-upload)
Posted by: sebastian.h10

 

Very likely the Universal Auto-Rewind Spool Holder also helped.

I have read this same thing on many forums.  I use a slightly different version, with gravity rewind instead of using a plastic spring.  You can find it (designed for a 22 cup Rubbermaid connector) and a desiccant holder to attach to the lid in the link to my collection, above.  There is also a larger sized gravity rewinder if you do not need it for a small container like I did.

Posted : 30/07/2019 12:35 am
CybrSage
(@cybrsage)
Honorable Member
RE: Successful MMU2S Modifications (re-upload)

I found the original sized gravity feed rewinder for anyone who wants it:

https://www.thingiverse.com/thing:3691892

Posted : 30/07/2019 12:46 am
hartpa@volny.cz
(@hartpavolny-cz)
Active Member
RE: Successful MMU2S Modifications (re-upload)

I successfully use gravity-controlled unwinding spool 

https://www.thingiverse.com/thing:3766912

 

Attachment removed
Posted : 06/08/2019 11:55 am
vintagepc
(@vintagepc)
RE: Successful MMU2S Modifications (re-upload)

The buffer also gave me no end of trouble with AB PLA, which has a rough surface finish. Just too much friction in the path to get it to work, even when "normal" PLA is fine. But I get beautiful tips with it if I use an auto-rewinder. 

Posted : 06/08/2019 12:24 pm
CybrSage liked
Iamjorgensen
(@iamjorgensen)
Active Member
RE: Successful MMU2S Modifications (re-upload)

Thank you, thank you thank you for the tips!!

Finally I am there - my first successful print with hundreds of filament changes! The extruder change & ptfe tube change did the magic. I have not changed the MMU selector yet - I had to intervene three times without understanding why exactly, but this was in the last step when flament goes into the MMU unit....could be I will try that last mod as well. 

Here is my machine in action - also with my own filament feed system. Have not published this yet as I would like to test it some more first. 

 

Posted : 10/07/2020 6:44 pm
Mattia
(@mattia)
New Member
RISPONDI: Successful MMU2S Modifications (re-upload)

@iamjorgensen

Today they will deliver me my MMU2S and im very excited about it 🙂 so.. im following all the mods that can be helpfull 🙂
may i ask you about the feeding sistem? thank you so much 🙂

Posted : 17/05/2021 7:22 am
FlashTech
(@flashtech)
New Member
RE: Successful MMU2S Modifications (re-upload)

I was thinking about trying these specific mods as well as investigating the Prusa "+" upgrade MK3S+ and MMUS+. I couldn't find any Prusa MMU2S+ documentation except for on github https://github.com/prusa3d/Original-Prusa-i3/releases/tag/R6

I did previously stumble on "vertex3d MMU2S+" but I figured it might not have the "Prusa +" updates from 6 months ago and wasn't sure about reprinting everything.

Before I decided what mod to print first today, I stumbled on vertex3d MMU2S+ prusaprinters post and it looks like they have taken in to account Prusa's "+" update from 6 months ago. https://www.prusaprinters.org/prints/69054-vertex3dorg-mmu2s-extruder-unit

I did some rough stl comparisons between Prusa's "+" upgrades, the mods posted above by MakerMathieu, and the latest "vertex3d MMU2S+" from my previous link. I have decided to go with vertex3d. I figure I'd mention this here just in case someone else is looking around for options.

I'll try to follow up with my results. My biggest issue right now is I get filament load failures often in single & multi filament mode with a sharp filament tip and a freshly replaced extruder ptfe tube didn't seem to help.

I have a "Prusa MK3S MMU2S" that I will be modifying.

Posted : 14/06/2021 4:08 pm
Baklin
(@baklin)
Reputable Member
RE: Successful MMU2S Modifications (re-upload)

@steven-6

 

I had seen that vertex3d mod on PrusaPrinters but not really looked at it. I like the way they trigger the filament sensor.

But there are a few others that do something like that in a little different way.

 

TZB MK3S+:MK2.5S+/MMU2S Extruder (MMU2S NO TOWER!) V3 This is the one that I use at the moment. And like a lot.

 

ESTRUSORE MK3S+ > MMU2S SENZA TORRETTA ESTERNA DEL SENSORE DI FILAMENTO This one was posted two days ago. I'm going to print this one and have a look at the parts before I maybe install it.

 

But I have to say that I didn't have much problems with the MK3s+ and MMU2s. Two reasons I wanted to remove the chimney. Adjusting it is tricky to get right and it got in the way of my PTFE tube when printing close to max Z height.

Let us know what you think of the vertex3d version when you have it installed.

 

 

Posted : 14/06/2021 9:20 pm
PrintingD
(@printingd)
Active Member
RE: Successful MMU2S Modifications (re-upload)

Hello. I don't know the best place to post this, so I'll try here for starters.

Like others, I wanted to make an MMU actually work. I actually finally did. I wanted to share what I learned.

Things I learned along the way.
If you do ALL the stuff I mention here, you too will be able to print a 33 hour print in 5 colors with >700 tool changes and NO intervention at all. My MMU2s finally works now!

BUILDING i3 MKS
1. Read the comments in the assembly instructions online. Some of the comments are better than the instructions.
2. READ THE ASSEMBLY INSTRUCTIONS very carefully.

BUILDING MMU
1. Patience. And read the instructions and comments on everything. A few steps are clunky but they do work.

CHANGING NOZZLES:
- changing to different nozzle size is a cool idea. BUT you must have the proper numbers for your filament and proper z calibration or you are cooked.
- MISTAKE I MADE: I used a 0.6mm nozzle but did not have proper settings for filament, did not have perfect Z axis calibration AND did not perfectly screw in the nozzle. All these conspired against me
- Changing the nozzle with a socket wrench is a good idea. Touching the metal part of said wrench after touching a nozzle at 285C is a bad idea!
- If a nozzle is not fully screwed in, filament will leak around the sides and up the heated box around the nozzle. This problem is not immediately obvious, but after several hours of print there will be lots of filament in places that it shouldn’t be around the nozzle, which then drips on to the model and fails prints

Z CALIBRATION
- There is a great video I watched on this on youtube. It show that gentle pushing fingers across the filament causes no movement. Before watching the video, I was certainly doing inaccurate Z calibration.
-
- Also of course the picture here is very helpful from Prusa guides:
- https://help.prusa3d.com/en/article/first-layer-calibration_112364/

TEMPERATURE OF FILAMENTS
- I have played with this a bit. When a filament temp is too low, it will make a sickening sound and nothing comes out. When it is too high, there are more drips of stray filament. Sometimes I use the tune command to change things around a bit. It turns out that I played with this stuff TOO much, assuming everything else was correct, when in reality I was compensating for problems with the nozzle or poor bed leveling, and it was rarely needed.
- There is a thing called a temperature tower which I have not tried but seems very helpful for experts
-
- https://www.thingiverse.com/thing:2729076
- The room ambient temperature fluctuations can impair adhesion and other things! Window open with wind vs closed gives me different results. Direct fan wind blowing at a printer from across the room affects prints. Watch out for this stuff!

MODIFCATIONS TO MMU
1. The buffer replacement - NEEDED!
- The buffer, after carefully building and setting it up, is total junk. I used it, found it was very difficult to load up with each new filament, and realized that it works very poorly. I disconnected it and tossed it.
- Tried the auto-rewind, the gravity auto rewind, the linear auto rewind. They either failed immediately, or not long after trying them out for a short time. They are REALLY COOL, but not designed to last.
- VERY HELPFUL - I like this and printed 5: from Michael Fanto - gravity spoolholder - more robust, worked much more often https://www.prusaprinters.org/prints/10370-gravity-spoolholder-for-mmu2s

2. Friction and blockage:
- VERY HELPFUL - The 5 ports in the back of the MMU2s have a kink in the angle, which increases friction, and was a place where filament would get stuck but would be hard to service. Therefore, I added this mod: PFTE passthrough M10 holder adaptor to decrease friction IMMEDIATELY helped resolve some filaments getting stuck issues: https://www.thingiverse.com/thing:3233579
- OPTIONAL SLIGHTLY HELPFUL - Replacing the PTFE in the back of the MMU2 as well as the PTFE between the MMU and the extruder with a wider diameter - I used inner diameter 3mm and outer 4mm, clear PTFE from amazon. This was not required, but it dramatically reduced friction, made it easier to load and unload filament manually, easier to see exactly what was happening everywhere, and provided more room IN CASE of bad tips. (see tips below) https://www.amazon.com/gp/product/B07F5Y284C/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
- OPTIONAL SLIGHTLY HELPFUL: Simple improvement to allow a passthrough PC4-M10 at the top of the extruder. NOT required, but makes things easier because I would often I was taking this part on and off. https://www.thingiverse.com/thing:4850222/comments. The PC4-M10s can be found here https://www.amazon.com/gp/product/B01IB81IHG/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

3. The IR sensor
- Many people complain about problems with the IR sensor at the level of the extruder. I did not realize for quite a long time that this was my problem too until I sorted out the above issues. Then I found that the IR sensor was a disaster - at first it worked sometimes, then it became unstable after not too many test prints and finally was unusable. What I mean here is that the sensor must detect the filament in between the gears. There is a very incomplete document here from Prusa https://help.prusa3d.com/en/article/ir-filament-sensor-calibration-mmu2s_2245/ which I thought should solve everything. It did not. I reached out to Prusa via email, and was told to follow those instructions. They failed. I reprinted the relevant part in PETG, that failed too.
- Then I finally started to understand what this stuff actually does. It turns out, that the filament getting between the gears actually pushes the idler a little bit to the side, since things are held together with a giant screw that has a spring on it. When it moves, the tower is supposed to move too, but thanks to the level formed by a different long screw, it more like rotates. That is all in theory. In practice it is not well designed and failed to work for me after many attempts and support helping.
- EXTREMELY HELPFUL MOD - At this point I tried this mod and within minutes the IR sensor became stable as a rock: https://www.thingiverse.com/thing:3554066. My only issue was I printed it flat instead of standing up as recommended, so I had a lot of support material and I needed to sand it down a little to reduce friction. Once done, PERFECT!

4. Tips
- As I was fixing things, I would find that sometimes the filament would fuse two different colors together, and have either a blob or stringy hairy bit at the tip that was being ejected from the printer. These bad “tips” are a common thing that is discussed on Prusa message board and all kinds of ideas are out there what to do about them, including very fancy post-processing python scripts for GCODE. I was going to do that, and I was also going to print a mod for the selector that many people seem to swear by, specifically because of the misery with the tips that kept on clogging up everything and causing numerous problem. BUT! There were two secret things I found.
- EXTREMELY HELPFUL MOD: The following settings change my tips from being terrible constantly to being perfect ALWAYS. Go to prusslicer, filament settings (for EACH filament type you use with MMU!)—>Advanced —>Number of cooling moves CHANGE THIS TO 3. Then click RAMMING SETTINGS, and change Ramming time to 3.0s. The former was recommended deep in some support document from Prusa, and the latter was recommended by a Prusa support agent via email. Therefore these are not HACKS, these are suggestions from Prusa. They are so incredibly helpful, they should have been default.
- I wanted to print a modified selector to help with the tips issue, but I decided against it because as soon as I did the software change above, I no longer had ANY problems with tips. At all.

5. Other stuff
- horizontal low profile frame holder https://www.thingiverse.com/thing:3418267C - tried this for a while, seemed nice but then realized the big problem was that when small filament bits are cut by the selector, they can end up anywhere, including in the direct path of the selector and then jamming the whole mechanism. I uninstalled this.
- The positioning of a rewinding system relative to the MMU2s is a non-trivial issue. Everyone’s setup will be different here, but my gravity rewinders worked better after I changed around the positions of things.
- The gravity rewinder from Michael Fanta mentioned above sometimes has a side piece that pops off. Superglue solves that.

 

Posted : 08/07/2021 5:12 pm
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