Hopefully it will be available soon regards joan

Cheers,  Eric

Posted by: @dormouse

Has anyone created an updated extruder pass-through mod (like https://www.prusaprinters.org/prints/3676) for MK3S+? That one has an "R4" on it, which I think means it was designed for MK3S.

The amount of negative posts about the mmu almost turned me off to it. Figured I’ll try it myself and see.  

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.
- https://www.youtube.com/watch?v=xM6LTaYDFLQ
- 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://youtu.be/_PNEjuiiqhg
- 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.

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.