MMU2S - Almost got it, but blobs on the purge tower are killing me!
So after much struggling and I'm getting so close to a reliable MMU2S. Tip are looking great, no extruder clogs and filament changes seems to working ok.
The only issue left to solve are these blobs that form on the purge tower.
This is happening in the initial load after a filament change. So basically the MMU2S feed filament to the extruder, IR sensors triggers and MMU2S idler releases. So far so good. Now this next part is where I see the blob form. The extruder continues to load filament to the extruder (the extruder is still stationary at this point) then it backs filament out slightly - It is just before the filament is backed out that a little blob is pushed from the extruder and creates a bump on the purge tower. The extruder then returns to loading filament again, the print head begins to move along the purge tower and the print continues as normal.
Now I have completed 2 prints with zero intervention even tho these bumps are on the purge tower. Usually the printer can push over them them with a small bounce. However if the print requires intervention of any sort the heat is shut off. This allows the build plate cool which in turn causes my prints to release from the print bed. I'm using this Powder Coated PEI sheet from MatterHackers. I really do not have any other adhesion issues with this plate. In fact my I really love it. Both PTEG and PLA stick like glue while it's hot and almost just fall off once it cools. Normally this is perfect, except when the MMU2S fails and shuts off the heatbed.
Well OK the parts don't exactly fall off, I mean they still have some adhesion left to the plate but it's not as strong as before the cooldown. This is where the bumps on the purge block are killing me. I have only had limited success with resuming a print after the bed has cooled. I know this partially because the bed has cooled and allowed some release but every failure after this point has been because the print nozzle catches a blob on the purge tower and breaks it free from the print bed.
The first picture I took this morning. The MMU2S required intervention and had paused the print. I fixed the issue and hit resume expecting the purge tower to immediately break free BUT it did hold for another hour until another blob finally broke it free.
I almost certain there would still be enough adhesion to finish a print if I could get rid of there blobs. This was so close... It almost made it.
So as mentioned even with these blobs I have managed to complete my prints if the MMU2S does not stop for intervention and allow the heatbed cool. But still I am concerned these blobs may eventually cause a collision or a layer shift.
Are there any settings in PS I can play with to try and adjust this? I have tried changing the Filament parking position and Extra loading distance. I have tried adjusting the numbers up and down of each setting individually and also adjusting both at the same time. I can see my changes having other effects on the purge tower but nothing seems to get rid of this blob issue. Is this something that needs adjusted in the MMU2S firmware instead?
I'm getting so close to success... or throwing my MMU at the wall. It's an emotional rollercoaster. Can anyone please help me keep this on side of success?
Best Answer by vintagepc:
Bah, this forum doesn't even notify you on mentions, I stumbled on this thread.
But yes, firmware alterations are required to deal with the fact the skelestruder is 10mm shorter from gears to nozzle.
They are in mmu.cpp which is where the loading routine is handled, around line 1463.
Kinda hard to tell from your pictures, but you are running the beta IR arm, right? If so, make sure it activates reliably. If it reports 0 constantly or intermittently it'll cause the MMU to keep shoving more filament through the system and that can also create blobs.
RE: MMU2S - Almost got it, but blobs on the purge tower are killing me!
Looks like I do in fact have enough bed adhesion to complete a print even after it's cooled down and reheated. I have enough half sheep already so I decided to just this go even though the purge block has broken free.
It was a mess but the sheep have prevailed! I'll take it as a win but still it was involved luck not complete reliability.
I have some better pictures of the blobs on the purge block. You can see it happens on almost every layer.
EDIT At least I thought they were better pictures. They seem fine while I'm editing this but they get distorted when I save the post. Hopefully you can still see my issue.
Even on the bottom layer. You can see where a small blob was deposited during the first filament change.
Think other wise my purge blocks look OK. Certainly much better then where I started from.
This print is Prusament Galaxy Black and Eryone Marble PLA. I have also tried MatterHackers Builds Series PLA and the Grey PLA that comes with the MK3. I'm getting this blob with all of them. I'm using PS stock settings from MK3s/MMU2s profile (Expect for trying to adjust Filament Parking and Extra Loading distance). I've tried the Prusament PLA, Prusa PLA, and Generic PLA filament profiles.
RE: MMU2S - Almost got it, but blobs on the purge tower are killing me!
What extruder is that? Bear? How does it's distance between the gears and nozzle compare to the factory extruder? If it's shorter (which I think I've read that it is) the blob issue would be that it is feeding more filament than it really needs to. If that is the case you'd need to determine the difference and adjust settings accordingly (not sure which, sorry).
As far as cooling down while waiting on manual recovery, the bed should not cool off, only the nozzle. My bed has stayed heated for 15 hours while waiting for my attention.
RE: MMU2S - Almost got it, but blobs on the purge tower are killing me!
If you're not using a stock extruder then you'll need to adjust the printer parameters. Look under the "Single Extruder MM Setup" under the "Printer Settings" of PrusaSlicer. I think some combination of Cooling Tube Length and Cooling Tube Position will probably get you there.
But if you have the option, I'd recommend going back to the stock extruder and getting it to work with that first. Getting the MMU2 to work is still a little bit of black art, so the fewer changes from stock the better. Once you have it working with the vanilla parts then try customizing things.
As for the bed cooling down, that shouldn't happen. The printer will cool the extruder but leave the bed hot. Is it possible you're using a custom or old firmware?
RE: MMU2S - Almost got it, but blobs on the purge tower are killing me!
Thanks for the replies.
So yes, you see I am using the Skelestruder by JLTX. I could go back to the stock extruder (I have both MK3 and MK3S parts) but I'm really trying to avoid this at all costs. Mainly this will require more than just an extruder change. I'm using most upgrades JLTX has made for the MK3 so switch back to a stock extruder will also require rebuilding stock X and Z axis as well. I would also need to order the 4x1.85x45 PTFE nozzle tube again as I have needed to trime mine down to 37mm to work with the Skelestruder. I will keep this in my back pocket as a last ditch effort before giving up completely. For now I have made so much progress to get this going and I'm so close... I still some patience to muck about with different settings to get this working with the Skelestruder.
For the heatbed maybe I need to pay better attention. I usually print PTEG, I have only gone back to PLA to get the MMU going. It's possible I'm so used to a 90c bed temp that 60c setting for PLA seems barley warm in comparison. I am using a custom compiled firmware for the Skelestruder but I can show all changes that are different from stock. I don't see anything that would affect the heatbed. I will pay better attention to the temp next time the MMU needs intervention. I just assumed it was cooling with the nozzle since my purge block has only broken loose after an intervention was required. I guess this could be a coincidence?
At this point, I almost feel like it's just a lack of understanding what I should be tweaking that is preventing me from getting over this last issue with the blobs. I haven't tried mess with Cooling Tube Length and Cooling Tube Position as I figured that would affect my tips more than the blob but I will give those a try. As I have been working with the MMU, I was only using the short PTFE tubes (that came with the buffer) out the back of the MMU. I am not using any type of buffer or rewind spool holder up till now. The last 3 interventions have actually been because the filament had fallen out the back of the MMU, lol. You don't hear that problem often. Usually people are switching to bigger ID PTFE because filament tips are to big and getting jammed in places. I have gone back to the long PTFE tubes into the MMU because I needed to add some friction to prevent filament from falling out!
As for the difference in extruder length and the related settings under the "Single Extruder MM Setup".
I feel like things are thing should be able to measure or otherwise derive from things I can measure.
I have taken some other rough measurements. I can disassemble the Skelestruder if more precise numbers would have a drastic effect. For these I would say they accurate within 1-2 mm. Also I realize you can't see the tip of the nozzle in the following pictures but this will more clearly show the upper parts of the sklestruder. Other than a shorter 37mm PTFE nozzle tube shown above, the V6 is the same as stock. Measurements here are from the tip of the nozzle and up.
So from these pictures I have assumed starting measurements for 3 out 4 settings under the "Single Extruder MM Setup", leaving only "Extra Loading Distance" as a random variable I would think could affect this blob issue.
Assuming my measurements are within reason would these settings seem a good starting point? I'm taking guess as to what portion of the hotend is actually considered the "Cooling Tube". Would you measure thing differently?
Cooling Tube Position = 35
Cooling Tube Length = 30
Parking Position = 75
Thanks again
RE: MMU2S - Almost got it, but blobs on the purge tower are killing me!
So yes, you see I am using the Skelestruder by JLTX. I could go back to the stock extruder (I have both MK3 and MK3S parts) but I'm really trying to avoid this at all costs.
No need to go back, the Skele does work. Hopefully @vintagepc will chime in as he is using the MMU with a Skele. He should be able to offer his setting tweaks.
RE: MMU2S - Almost got it, but blobs on the purge tower are killing me!
Sorry about these picture guys. They look fine in edit mode but distort when I post them. I found if I right click on an image and "open in new tab" the display as intended
RE: MMU2S - Almost got it, but blobs on the purge tower are killing me!
Sorry about these picture guys. They look fine in edit mode but distort when I post them. I found if I right click on an image and "open in new tab" the display as intended
Its not you, its the forum.
The best option when posting pics is to use the Add Media option. When you select your image (only do one at a time) there will be settings on the right for how you want it included. Medium is a good option and make sure to select the option to link to the original image.
RE: MMU2S - Almost got it, but blobs on the purge tower are killing me!
Bah, this forum doesn't even notify you on mentions, I stumbled on this thread.
But yes, firmware alterations are required to deal with the fact the skelestruder is 10mm shorter from gears to nozzle.
They are in mmu.cpp which is where the loading routine is handled, around line 1463.
Kinda hard to tell from your pictures, but you are running the beta IR arm, right? If so, make sure it activates reliably. If it reports 0 constantly or intermittently it'll cause the MMU to keep shoving more filament through the system and that can also create blobs.
RE: MMU2S - Almost got it, but blobs on the purge tower are killing me!
Kinda hard to tell from your pictures, but you are running the beta IR arm, right? If so, make sure it activates reliably. If it reports 0 constantly or intermittently it'll cause the MMU to keep shoving more filament through the system and that can also create blobs.
Yes I have switched to the beta IR arm. As best I can tell watching the IR sensor value in the support menu it seems to be triggering reliably. I have some people say it actually flicker 0-1 quicker than the LCD can update so if anything it's happening super quick but not registering. As far as I can see, it's value changes 1 when filament enters the gears and remains solid unti filament is retracted for change. Then value is back to 0.
I'm gonna give those firmware changes a try next.
With regards to the under the "Single Extruder MM Setup" - Forget about my number posted above. before I make these firmware changes I am having the best results with using the MK3S/MMU2S printer profile as a starting point and these settings.
Have you switched to the "S" profiles when you added the IR sensor? Could you please share your settings for "Single Extruder MM Setup"?
Thanks
RE: MMU2S - Almost got it, but blobs on the purge tower are killing me!
@vintagepc
That's it - It worked! Where do I send the beer?!
The default retraction number was 58 in the MK3S 3.7.2 firmware but I just subtracted 10 from the values I had.
Described perfectly in the comments, this was exactly when it created the blob.
I also had to readjust the "Extra Loading Distance" after I flashed the updated firmware.
Thanks again - I'm fairly certain it's all gonna work now!
RE: MMU2S - Almost got it, but blobs on the purge tower are killing me!
Awesome!
FWIW the parameters I have on that page are:
30, 10, 75, -13
IIRC there is no difference between the S and Mk3 profiles. But I'm using Bobstro's ones currently with appropriate tweaks, so it's a moot point 🙂
RE: MMU2S - Almost got it, but blobs on the purge tower are killing me!
As far as cooling down while waiting on manual recovery, the bed should not cool off, only the nozzle. My bed has stayed heated for 15 hours while waiting for my attention.
Just as a follow up here, I have switched back to PETG and had have just a print requiring intervention. I can confirm the bed is in fact still very hot after the printer sat for several hours waiting on me