The newer versions of Slic3r have a new button under Advanced Filament Settings for "Ramming settings."
Clicking this button brings up a scary-sounding warning dialog saying that you shouldn't mess with these settings unless you really know what you're doing. Ramming is apparently a rapid extrusion the MMU performs just before unloading a filament, in order to ensure the tip of the filament is properly shaped.
Presumably at some point some of us will need to mess with these settings, but I haven't found any information about when it might be appropriate to adjust the ramming parameters, and how to tell if the ramming is correct or not.
Any pointers? Looking at a handful of the supplied filament profiles, it appears that many all use the same ramming settings (which extrudes 20 mm3, or a little over 8mm of filament) though a few of them are different.
I'm not planning to mess with this right away, but with the wide variety of materials I have in my collection it feels like I should have a handle on how this works because eventually I'm going to need it.
Re: Ramming settings
Generally, ramming parameters are determined by the tip on unload.
Honestly, I have a job understanding Slic3r settings for this. Basically, I ram as fast as possible; the ram volume determines the shape of the tip:
Less ramming - short tip plus and more stringing
More ramming - longer and thicker tip and less stringing
13 mm^3 is about right for most PLA, 15 mm^3 seems better for BVOH
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
RE: Ramming settings
This thread is pretty old. But I am hoping someone is alerted and responds if they have an answer.
But referring to the photo, you can see I'm having trouble with fat filament ends on MMU2S prints using PLA at 210 C acquiring fat ends with a pigtail 10 hours after the print starts. I have cooling moves set to 2 but have not touched other expert settings. But its strange to me why its giving trouble so long after the print starts. What are the factors in play ? Could it be moisture ? The filament starts off dry but could it acquire enough moisture in 80% RH in 10 hours to become stringy. This IS PLA, not supposed to be so hygroscopic as other filaments.
The actual symptoms: several:
(1) Filament gets pushed out the back of the MMU so that it cannot be grabbed next time it needs to load. Eventually when it tries to load its LED just flashes red after trying lots of times. I assume that this is due to the pigtail string on the end keeping the finda at 1 as its pulled through, causing the retraction to go on a bit longer.
(2) Filament jams in the MMU between the bondtech gears and the selector.
(3) at the end of the job, filaments cannot be pulled back onto the roll through the PTFE's. I have a solution for this one which is to upsize the PTFE Inside Diameter, but I have not yet deployed it. Instead I have resorted to using the cutter on every filament at the end of every job. It is messy but it works if the filament can be coaxed into poking its head out the front to be chopped off square.
I am looking at Ramming settings, but note most people are using it for filaments like PETG, much more stringy than PLA. So is it appropriate for PLA ? And what is a good set of values to use ?
Can filament cutting be put to good use in this circumstance ? Cutting normally occurs automatically when enabled, only when there is unsuccessful attempt to load. But seems t0 be no way to enable cutting on every unload. Yes, I am awate that cutting makes the filament end square, and could cause loading issues on subsequent filament changes. But on limited sample size where I have seen it operate, did not seem to cause that to happen.
I've also noticed that there are not many recent comments that mention ramming. It went quiet some time ago, prior to launch of MMU2/S. Why ?
RE: Ramming settings
Sorry, no answer, but am on the same journey to a solution. I have always had the same problem. For years. Even gave up the main advantage of the MMU and only use printer as single spool. Am trying different ramming settings currently. Will post if improvements found.
RE: Ramming settings
There is some hope for improvement now regarding MMU2 firmware anyways. On recent Prusa podcast (#45) (YouTube) on Friday Josef Prusa responded at the 1 hour mark to somebody's question about the MMU, and his response was that the development team are presently working on "refactoring" the firmware code.
Now, I have previously looked at the firmware code and nearly threw up. It is spaghetti code only a newbie programmer would be proud of. Like they never heard of object oriented programming in C++. just a bunch of functions thrown haphazardly into files with no real structure, and deuced difficult to analyse. Dangerous even, because you could change something in one place, but break something elsewhere unwittingly.
But it has run the MMU for thousands of customers for a couple of years now. But is that what "refactoring" is to hit ? (no idea). Josef's very brief sentence on the subject gave no details. But it gives some hope because at least they are working on improvement, so its not a dead project (which some might have thought, because of XL coming on ....)