To MMU2s or Not to MMU2s?  

RE: To MMU2s or Not to MMU2s?

Different materials are challenging with the MMU, different colours, especially if you want to print PLA should work fine, once you've dialed in the MMU. There are people without any replacement parts who got it working pretty much straight away, others had to invest more effort.

I think here in this forum the negative experiences are overrepresented, makes sense, after all why should you post if everything works fine? That doesn't mean that the MMU isn't finicky, or can need some tweeking if you are out of luck.

RE: To MMU2s or Not to MMU2s?

@jiral

Ok, that makes a lot of sense. While I love the idea of trying to print say, an enclosure out of PLA with bumpers made of TPU, I don't think I'll be trying that. I've never even gotten the nerve to print TPU without the MMU!

Thank you!

RE: To MMU2s or Not to MMU2s?

The MMU2s works perfectly if:

1) You follow the build directions exsctly and use common sense, and

2) you have a perfectly working MK3s.

@jiral is spot on - the only posts you usually see are from people having issues. And in trying to help many of them what I realized is they didn't do #1 and/or #2 above. The list of things people do is astounding - they crack a part and instead of printing a new one they glue it; use the wrong screws because they think the directions are wrong; use a "better" part they found on Thingiverse before they have even finished the build, etc. 

I have an MK2 that has run for 4 years flawlessly. I have an MK3s that has run for 2 years flawlessly  I have a Mini that has run for 4 months flawlessly. And I have a MMU2s that worked out of the box and has run 3 months flawlessly.  Go slow, follow the directions exactly. If things don't fit then stop and figure out what you're doing wrong, don't be in a hurry and don't mod anything. Use the latest software and firmware with standard settings. If you follow these guidelines you'll be happily printing with 5 filaments in no time.

Good luck.

RE: To MMU2s or Not to MMU2s?

@steve-e3

Thank you for the confidence boost! I took my time building my MK3s mostly because I was having such a good time I didn't want to finish! It's been working amazingly, such an upgrade from my last printer.

What's the feeling on MMU2 clones? I'd prefer to buy original but they are hard to come by at the moment. I've been watching this one:

https://www.aliexpress.com/item/4000117685175.html

The only part I don't understand is why it doesn't come with the M5 insert nut for the pneumatic fittings. I don't see how it would be usable without them.

Thank you!

RE: To MMU2s or Not to MMU2s?

Posted by: @jkoffman

Hi all,

 

I'm considering starting the search for an MMU2s for my MK3s. I have been watching the forum, and there seem to be a lot of people happy with theirs, but also a lot of people....less pleased.

 

I'm looking to use the MMU to get multi colour printing on enclosures I make for various things I build. I am not looking to print different materials, just different colours.

 

Is it reasonable to expect that with some tweaking, printing of replacement parts, etc I should be able to get the unit working smoothly?

 

Thank you!

Mine actually worked fairly well when first assembled.  It does, however, have its shortcomings, and I worked around some of them and I'm going to do some more extensive mods (MMU2S switch, tube quick release) as soon as I have some down time and some breathing room.

One suggestion I might make for the initial tests of it is to simply use some short coils of various color filaments instead of loading up the buffer and such.

For everyday stuff, I plan to continue to use the printer with the MMU2S disconnected, and connect it for multi-color prints and when I want to do soluble supports.

RE: To MMU2s or Not to MMU2s?

"What's the feeling on MMU2 clones?"

I don't have any experience with the clones. But realize if you go down that path, you'll essentially lose all the support this forum provides as their feedback and experience will be based on the Prusa hardware, not what you have. You need to find a forum on Alibaba and brush up on your Madarin. 😧 

"Is it reasonable to expect that with some tweaking, printing of replacement parts, etc I should be able to get the unit working smoothly?"

Now why do you think you need to tweak it to get it working properly? Re-read my previous post - the MMU2s, like any Prusa product, has been through hundreds of hours of engineering design and thousands and thousands of hours of testing and works for thousands and thousands of users. Why do you think you need to mod it to get it working?

If you want to know why there appears to be so many people with issues, consider these actual quotes I captured from the MMU2s online assembly manual:

"I tightened mine too much as I didn’t read all the way down the instructions before proceeding. I cracked it and tried to glue it, but I believe the crack was exacerbated by tightening the two tension spring screws down too far on the idler assembly. Because the screws were loose on the extruder motor shaft due to the crack, the idler was shifting off the filament and not allowing the gears to grab it sufficiently to either load or eject properly" [Using a cracked/glued part instead of printing a new one]

"M3x10 screws didnt work for me for the top two holes, I had to use M3x14 screws for them." [Didn't realize the nuts were missing so wrong screws used instead to compensate, may interfere with other attached parts and he will again use the wrong screws later where it requires the now missing M3x14 screws]

"I flared the ptfe tubes behind the selector on all 2 parts and now it's much better. I don't understand why you insist on saying that they are flared only on the outside" [Absolutely no need to flare the PTFE tubes that Prusa supplies...modding the design before it's even working and not even knowing why, discounts the engineering behind the design]

"After some jams during assembly I also had to use superglue." [No directions anywhere ever call for gluing components together]

"The thermistor I got is a cartridge with a short “pigtail” connector" [Using after-market non-Prusa parts and complaining it doesn't have the correct connector.]

(The last one was one of my favorites - he said it would take to long to get a new thermistor from Prusa so he ordered it from Amazon and it came with a connector different than Prusa's wiring. He then proceeded to tell Prusa they should change their wiring on their printers LOL.)

In another post there is a user that while building his MMU2s he just threw out Prusa's FINDA sensor housing (which is a critical part for proper operation) because he found a "better" one on Thingiverse which looked like some Rube Goldberg contraption with a magnet. That was bad enough, but he also didn't read the user comments from the people that reported it didn't work for them.

And you figure for every 1 person that leaves a comment on the online assembly manual, there's a hundred more doing something stupid but that don't comment. Now you can see why there are so many posts of people having issues, they aren't following directions and paying attention to detail.

If you go ahead with the MMU2s I would recommend:

• Make sure your MK3s is printing perfectly with default slicer settings before you begin.
• Check the rev of the printed Prusa parts you receive against the latest rev posted on Github and print any newer posted versions.
• Clean up the printer parts. Where there is a hole in the part, take a drill bit and clean it out. Use an Exacto knife to clean grooves. If parts don't fit together correctly STOP, figure out why and fix it. For filament paths take a piece of filament and make sure it smoothly and easily follows the path.
• After completing the MMU2s, use the MMU2s in single filament mode, no buffer. Do this with each of the 5 ports. Make sure you can load/unload filament with no issues. Make sure it works perfectly.
• Install the buffer and 2 filaments (PLA). Download the gcode for the Prusa test model (LINK) for 2 cubes and make sure you can print these.
• Work your way up to 5 filaments using Prusa gcode (to eliminate any Slicer issues).

Don't do this (which many are tempted to) until it's working reliably and then you feel like possibly breaking your new MMU2s:

• Mod the buffer or use a completely different buffer design.
• Mod parts on the MMU2s.
• Change the PTFE tubes (diameter, length)
• Add PC4-M10 Fittings anywhere in the filament path
• Use filament auto-retractors
• Screw around with Slicer settings like RAM speeds, cooling moves, etc. The MMU2s works perfectly with the default Prusaslicer settings.

Again - there is no reason to mod the design to make it work - tens-of-thousands of people are using it successfully unmodified. When folks mod their unit in order to make it work properly they are band-aiding over some other fundamental problem with either their printer or their MMu2s.

Good Luck.

RE: To MMU2s or Not to MMU2s?

@steve-e3

Fair points! I appreciate the in depth response. I'll see if I can find an original, it's how I'd prefer to go anyway.

Thank you for the confidence boost!

RE: To MMU2s or Not to MMU2s?

Posted by: @steve-e3

The MMU2s works perfectly if:

 

1) You follow the build directions exsctly and use common sense, and

2) you have a perfectly working MK3s.

@jiral is spot on - the only posts you usually see are from people having issues. And in trying to help many of them what I realized is they didn't do #1 and/or #2 above. The list of things people do is astounding - they crack a part and instead of printing a new one they glue it; use the wrong screws because they think the directions are wrong; use a "better" part they found on Thingiverse before they have even finished the build, etc. 

 

I have an MK2 that has run for 4 years flawlessly. I have an MK3s that has run for 2 years flawlessly  I have a Mini that has run for 4 months flawlessly. And I have a MMU2s that worked out of the box and has run 3 months flawlessly.  Go slow, follow the directions exactly. If things don't fit then stop and figure out what you're doing wrong, don't be in a hurry and don't mod anything. Use the latest software and firmware with standard settings. If you follow these guidelines you'll be happily printing with 5 filaments in no time.

 

Good luck.

 

I partially disagree. There is also a number 3: You've got luck.

While my previous main problem were loosened screws on the MMU idler, I also had issues with the tolerances of the extruder idler triggering the IR sensor. The latch was just a tiny bit too short, triggering but not 100% reliably, and not triggering when filament was too soft. Making that latch merely a tiny bit longer resolved that issue and made the sensor completely reliable. I don't think I made any assembling mistake there, it was simply a problem of tolerances.

That said, if it had not taken me that long to identify the MMU idler screws as culprit, I would have had almost instant, reliable success, I suppose. Others with malformed MMU idler bodies out of the box might not have been so lucky without printing a replacement.

PS: I think also the location of spools and the way you feed into the MMU has a big impact on reliability. I have settled with coming from below which bends the filament the least from spool to extruder and maintains a downward drill at the MMU which helps finding the path (upwards drill at that location can cause issues every once in a while but I think that is also mentioned somewhere in the manual)

PPS: I would recommend clone MMUs, not that I tried out any but given how delicate the original is I would not want to risk a clone with potentially additional problems. But in the end, its anyone's decision, it might work just as well, or not.

RE: To MMU2s or Not to MMU2s?

Posted by: @steve-e3

...

Don't do this (which many are tempted to) until it's working reliably and then you feel like possibly breaking your new MMU2s:

...

• Screw around with Slicer settings like RAM speeds, cooling moves, etc. The MMU2s works perfectly with the default Prusaslicer settings.

 

You are contradicting Prusa's own manual there. Depending on the filament behaviour they actually do recommend testing an additional cooling move, if reducing print temperature is not enough to get a proper filament tip. This might not be necessary for most filaments and indeed, it can cause major proplems itself if it is done when not necessary but it is an officially recommended optimisation possibility which one can test for.

Regarding mods, every one of them can cause more troubles than improvements, that is true of course and it is something one has to be aware of and accept. I have installed some mods myself and while they might not be necessary I found that they can make the product better or more comfortable to use. If further down the road I should come to the conclusion that they created new troubles, the'll get thrown out again. For example a not fully closed FINDA probe housing, offering access to the ball, is not necessary if everything works fine, but if you do work with filaments that simply are challenging to get completely string free, it is a great comfort plus if you can simply visually check the proper functioning of the FINDA probe and if need be also clean up the channels just as is recommended to do with the Extruder housing and the MMU housing once in a while.

I also use a larger diameter PTFE tube from MMU to Extruder (2.5 mm ID instead of 2 mm). I am aware that this might cause issues, but so far the only thing that changed was to make the whole system more robust if filament tips are once in a while not 100% perfect.

PS: I don't use flexible materials with the MMU so far. If I should use them, I would change the tubing again of course.

RE: To MMU2s or Not to MMU2s?

This thread started with the question - should I consider an MMU even though I've read you need to mod them to get them to work? I stand by all my points: 1) the MMU as designed and properly built works perfectly, 2) start with a perfectly working MK3s and 3) build the MMU2s properly and without any mods until at least it works perfectly.

It's not a matter of "You've got luck". A 3D printer is a mechanical machine, it's not based on luck, it's based on properly working parts. Take a look at the quotes above of how people have assembled their MMU and you'll understand why so many people have problems. If you receive a part from Prusa and during that assembly step you realize it's not quite right then certainly stop and print another part, that's common sense.

Once the combination is fully working for hours on end you'll have the confidence to make modifications and I totally agree can be useful. But for a new builder this just simply adds risk and complexity and usually ends in frustration.

With a complex mechanical device keep in mind the laws of unintended consequences - a simple mod may seem harmless but affect something else. The MK3s and MMU both have a lot of moving pieces and have to work perfectly together for the whole thing to work. As an example and to your point it seems like larger PTFE tubes should be better, but 1) many people start experiencing reliability issues after installing larger tubes and 2) don't you think if larger tubes were needed or made it more reliable Prusa would have designed it with larger tubes? Of course. Again to my point, Prusa (and thousands of users) successfully print on the stock equipment. If you are new to the MMU2s you should baseline your build by getting a completely stock and default MK3s+MMU2s working perfectly before considering any mods.

P.S. my standard Prusa buffer, with their recommended spool locations works perfectly, I have yet to have any reliability issues with their setup & Prusa has Q/A'd thousands and thousands of print hours with this setup.

Cheers!

RE: To MMU2s or Not to MMU2s?

Posted by: @steve-e3

It's not a matter of "You've got luck". A 3D printer is a mechanical machine, it's not based on luck, it's based on properly working parts. Take a look at the quotes above of how people have assembled their MMU and you'll understand why so many people have problems. If you receive a part from Prusa and during that assembly step you realize it's not quite right then certainly stop and print another part, that's common sense.

Mechanical parts have tolerances, those are higher with well produced 3D printed parts than with well produced injection molded parts. It is a matter of luck what kind of parts within those tolerances you receive. These precise measurements might have an impact on how robustly it works. Prusa itself acknowledges that in the MMU manual indirectly. Many of those cases can be addressed by post processing the parts, in some cases however, a reprint will be needed.

A reprint might be common sense, but it is in my books not simply part of a regular assembly process. It is not a mod either though, you are right in that regard.

I do agree with you however. One should definitely try getting the machine working properly first, before engaging with mods.

Using the standard buffer might have been a good idea, but that was my only 0 hour mod and I stand to it. That said, getting the rewinding spool to work reliably was also some work however, the exchanging of filaments is as far as I have seen more comfortable with them and from a purely aesthetic viewpoint I find it great to watch them un- and rewind. It also gives more feeback than the buffer by clearly showing back movements during loading and unloading. But yes, if I had tried the buffer first I could make a better founded comparison of those two systems. 

PS: I do not really care if Prusa saw a need for larger diameter tubes or not to be honest. I do see the benefit of a more robust system with them so far but my usage is not as broad as what Prusa intended the sytem for, so I do not necessarily think me or them need to be wrong, we might have simply different requirements.

RE: To MMU2s or Not to MMU2s?

Awesome - I'm glad it works for you!

For @jkoffman, you won't find a better deal than to be able to print not just 2 but 5 filaments for $299 USD. If you decide to take the plunge just follow my guidance above and you'll be fine. Good luck!

RE: To MMU2s or Not to MMU2s?

@steve-e3 Thank you! I hope I can find one!

RE: To MMU2s or Not to MMU2s?

@jkoffman

Finding an MMU2S is easy, just go here: https://shop.prusa3d.com/en/upgrades/183-original-prusa-i3-mk25smk3s-multi-material-2s-upgrade-kit-mmu2s.html#

Getting it delivered is already a bit harder in these current times. The shop shows a delivery time of 3-4 weeks but it also can take a little bit longer from my experience than what they list at the date of purchase. It's a bit of waiting time but not outrageous I think. It is not a Prusa Mini after all.

RE: To MMU2s or Not to MMU2s?

@jiral

I have a retailer in Canada that gets them. They're hoping to have some in July...so I'm holding off for now. We shall see!

RE: To MMU2s or Not to MMU2s?

@jkoffman

As far as I know Prusa does not have an official retail channel, if that's incorrect I'd like to know. (I've never seen a list of authorized resellers on their web site either)

Of course that would not stop a retailer from re-selling units, but then you may not be getting a 100% Prusa kit. I have seen many posts of people that bought from a reseller and the kit had different parts in it - obvious only after Prusa tech support tried to help them with an issue and a part was different, electrical cabling was different, etc 

If you don't buy directly from Prusa its Buyer Beware.

RE: To MMU2s or Not to MMU2s?

I got mine from someone here in the States who decided he did not want it.  It was a one-of-a-kind at a fair price and not a profiteer.  It was 'open box', never assembled, never used.  When I took inventory, everything was sealed and in there, except for the gummy bears.  😉

I would love for Prusa to have some official North American distributors, and I recall answering a query to that effect some time ago.  I checked, and I could not find any evidence of any.  Even the Stateside Filament PM firm, which sells what is included with every Prusa printer, does not use the Prusa brand name for it, even though they say it is from the Czech Republic.

RE: To MMU2s or Not to MMU2s?

Yup they would not be able to use the Prusa name without permission, it would be a trademark violation 

I don't think they have resellers for a few reasons, the first is that they don't need them - they're selling everything they make. The next is they would have to raise their direct price to meet the markup of the reseller,  which would raise the overall cost to the consumer. (You can't undercut your channel partners otherwise you won't have channel partners). And having a reseller isn't much help if they can't get any more product any faster than someone ordering direct from Prusa.

And 3D printing doesn't lend itself to VARs, there's just not that much value someone can add to a 3D printer, at least to most customers that enjoy tinkering and understand the machinery. 

What we need is more Prusa capacity!

RE: To MMU2s or Not to MMU2s?

@steve-e3

I thought that too, but there are many retailers in Canada that have relationships with Prusa. I don't know what the details are, but they are ordering in bulk and reselling. Prusa even drop ships for them if needed. They seem to deal closely with the company, and the pricing is consistent roughly with conversion plus duty. Close enough that they certainly aren't marking it up. The product is genuine, or someone is investing a hell of a lot of time to counterfeit this good.

I have no idea why this doesn't happen in the US. I find it all quite strange to be honest.