Additional layer height and nozzle profiles?
Before I start messing with things that I have no understanding of, does any one have profiles for the MMU in multi-filament mode to cover the additional layer heights and nozzles that are supported in Single mode?
RE: Additional layer height and nozzle profiles?
There may be some who have created these profiles but please bare in mind that the ones supplied are the only ones supported by PR for very good reasons.
Going lower with layer height or using smaller nozzle diameters will cause issue with ramming and purging, where you really do need the high volumetric feed rates which cannot be obtained when going lower/smaller.
Peter
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: Additional layer height and nozzle profiles?
Yeah that is what I've heard and how to go about tweaking all that is what I don't understand and will need to hunt and peck through while wasting filament. That's why I'm hoping someone has profiles to share that we can work from.
RE: Additional layer height and nozzle profiles?
It's not the tweaking that's a problem, it's the limits of the printer.
Say you are using a 0.25mm nozzle, you can't really extrude a line much more than 0.32mm and that's less than half the volume you extrude with a 0.4mm nozzle at 0.5mm line width. That means your X and Y movements need to be significantly more than twice as fast (about 2.35 times) - about 235mm/s, and that is simply not going to happen on the purge tower when you take into account acceleration 🙁
Peter
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: Additional layer height and nozzle profiles?
If you are laying down less volume through the nozzle, wouldn't you need to slow down the movement to match the result of a larger nozzle (assuming the same layer height)?
Honestly the .1 and .05 layer heights on the .4 nozzle are more interesting to me than a smaller nozzle (I do have .25, but haven't used it beyond early test prints).
RE: Additional layer height and nozzle profiles?
Maybe using a 2nd wipe-tower and then alternating between them could be a quick hack to cut the printed layer height in half. (e.g. 0.2 layer height for the wipe towers and 0.1 layer height for the printed parts)...
Another issue might also be the temperature. The MMU profiles seem to like low temperatures - at 0.05 layer height most of my filaments will most likely clog my extruder at these temperatures.
Still, I wonder if the wipe-tower would work with 0.25 nozzle using a really large layer height.
RE: Additional layer height and nozzle profiles?
If you are laying down less volume through the nozzle, wouldn't you need to slow down the movement to match the result of a larger nozzle (assuming the same layer height)?
Honestly the .1 and .05 layer heights on the .4 nozzle are more interesting to me than a smaller nozzle (I do have .25, but haven't used it beyond early test prints).
For ramming in particular and to a lesser extent the purging, there is a requirement for a high volumetric speed.
For ramming, you need to extrude between 12 and 20 (depending on filament) mm^3 quickly in order to cool the nozzle and have fresh filament in there in order to retract without stringing. So, smaller nozzles and lower layer heights need the XY travel to be faster to maintain the volumetric extrusion rate. The less you extrude, the faster you have to move.
Basically, your ramming time should be (say) 2.5 seconds, and in that time, you have to extrude 6 linear mm of 1.75mm diameter filament.
Peter
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: Additional layer height and nozzle profiles?
Still, I wonder if the wipe-tower would work with 0.25 nozzle using a really large layer height.
You really should not use layer heights > 80% of nozzle diameter, so 0.2mm at maximum. And as mentioned previously, that's less than half the volumetric extrusion of a 0.4mm nozzle, so 2.3 times the XY speed.
Peter
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: Additional layer height and nozzle profiles?
Thanks for the details @pjr. I only understood the basic purpose of ramming, not how it actually works. My assumption was that it retracted the filament outside the hotzone to let it cool slightly, then rammed it back in at high speed to crush and fuse any tail, and finally retracted it quickly to prevent another tail from forming.
I'm familiar with the concept of high flow rates having a cooling effect (e.g. compressed gas escaping), but I would not have expected that the extruder could push enough filament through to have any cooling effect on the nozzle.
Based on this I get that a .25 nozzle might be a tough nut to crack, but wouldn't a .1 or .05 layer height with a .4 nozzle be easier? Seems like @andreas-d10's idea of multiple towers (or a single larger where a single tower layer accounts for multiple part layers) has some merit. I guess that is a bit beyond simple profile tweaks though as that would be some fundamental changes to how the towers are created and utilized.