I wanted to share my findings with others having the same, or similar, issues with the MMU2. Before reading any further, just know that my hardware upgrade path has been as follows: MK2S
. And I have a Micro Swiss .04 hardened nozzle. No other mods/tweaks.
My solution was a combination of the following:
1. Switch out the heatbreak to the MK3 version: https://www.printedsolid.com/products/e3d-mk3-heatbreak
2. Definitely follow the advice in Chris Warkocki's video: https://www.youtube.com/watch?v=v1h-S7bxPEE
3. The only changes I've made to the default Slic3r Prusament PLA configuration are: "Loading Speed at Start" = 19, "Loading Speed" = 22
Please consider reading the rest of this post, as I'm sure many of you will benefit.
My Journey in Detail
Probably not unlike you, I have spent about a month trying to get my MMU2 to print reliably. I tried every combination of Slic3r settings. I watched Chris Warkocki's great Troubleshooting 101 video numerous times, and followed his advice exactly. I tried different brands of filament, including Prusament. I tried lowering the temperature as far down as 180 c., and as high as 220 c. I've read, and re-read, posts from this forum. I've monitored the MMU Github repo issues. Sound familiar?
I was at a point where I was confident that my filament path was clear of obstruction and any excess friction. And I felt I had done everything I could think of on the software side of things. I was left with the conclusion that Ramming and Cooling Steps seemed to have the most meaningful effect on the filament tips. But this is where I was stuck, and thoroughly frustrated. When I lowered the Ramming, the filament would get too stringy and inevitably jam during a load. When I raised the Ramming, the tips would come out better, but they'd be too fat causing it to jam on unload.
I was damned either way.
Not wanting to give up, I recalled someone on these forums mentioning that the heatbreak on the MK2S/2.5 is slightly different than that of the MK3. Neither my MK2.5, nor MMU2 upgrade kits came with any new heatbreaks. So whatever heatbreak came with my MK2S originally is the one I had.
Whoever mentioned the heatbreak difference said they were going to try the MK3 version, and report back. I could be wrong, but I don't recall ever seeing their conclusion. Did it work for them??
What Worked for Me
Having no other option myself, I decided to give the MK3 heatbreak a try. After all, nothing else had worked. So I placed my order on Printed Solid, and it arrived the other day. I promptly installed it: https://www.printedsolid.com/products/e3d-mk3-heatbreak
I wanted to eliminate as many variables as possible with the new heatbreak. So in Slic3r I did the following:
1. Reset my copy of the Prusament PLA settings back to its defaults.
2. Changed the "Loading Speed on Start" to 19, and the "Loading Speed" to 20. (These seem to be universally accepted as the correct
values to use).
3. Loaded up 4 rolls of Prusament PLA.
I have a simple model that allows me to print out a row of small blocks, each being a different color. It's what I've been using to quickly iterate on configuration changes, and seeing how it affects things. I kicked off this print, and studied it. As the MMU2 would switch colors, I'd push the recently-unloaded filament out and look at the tip. It seemed good, but I wasn't convinced yet.
I let this print finish, and to my surprise I didn't have any issues with loading/unloading. I once again pushed out each filament tip to inspect it. There was absolutely no stringing. And the tips no longer had the large bulge, which had previously been a tell-tail sign of inevitable jamming. The tips, to my surprise, actually looked... perfect.
Still not convinced, I loaded up the multi color version of the Kobayashi Fidget Cube. This is a print that I've never successfully printed before. It would typically jam during load/unload within 10 color changes. That wasn't the case this time. I monitored the tips during the print for the first couple of hours, and everything seemed to be working fine. Gaining confidence, I let it run for a couple more hours and checked again. Still fine!
I finally went to sleep and woke up this morning to a perfect print! This was two prints in a row where I didn't have a single jam or skipped layer!
I did seemed to resolve the issues. And I am 100% convinced that one winning change, is in fact the MK3 heatbreak.
Will this fix your issues?
Possibly. In fact, I'd venture to say "probably, yes" if my troubleshooting experience sounds anything like your own.
How can I be so confident after only a couple of prints?
To that, I say, I was at the point with my troubleshooting/iterating that I could quickly tell from the shape of the tips whether or not I was going to have issues. That, and I've never had more than about 20 color changes before encountering a jam. There is a noticeable improvement in the shape of the tips after swapping in the MK3 heatbreak. No stringing, just perfectly shaped tips.
I feel like I'm FINALLY experiencing the MMU2 the way Prusa intended it!
If you are at your wits end, and haven't tried this change yet, I strongly suggest doing so. It's a $20 part. And it would be great to get further confirmation from others.
This also begs the question: Why didn't Prusa include the MK3 heatbreak in our upgrade kits? If I'm right, in this being a fundamental reason why so many of us MK2S/2.5 users are having issues, they could have really saved a lot of people from the headaches.
I hope this helps someone else out there. This forum has been of tremendous value to me. And without it, I probably wouldn't have even through to try the MK3 heatbreak.
Does anyone have a specific model they'd like me to try printing? Maybe one that you personally have had trouble with? I'm just thinking it could help validate my findings, while simultaneously showing what could be possible for those in the same boat as I was