Counter-intuitive way to reduce stringing
When you have stringing/oozing, everybody tells you two things: 1) add more retraction (it reduces the pressure) and 2) reduce the nozzle temperature (it adds viscosity). Is this really the way to go? My MINI is proving the opposite.
After a regular maintenance, I fine tuned my MINI to print using a two years old PLA prusament (mystic brown). The result is that it prints the better quality using 210°C for the nozzle, and 1mm for the retraction length: with more retraction, it gives more strings; idem using a lower nozzle temperature. I used to print at a lower temperature when this filament was new, which gave my preferred color and finish. A lower retraction (0.8mm) gives the expected stringing and oozing nightmare.
The only upgrade from stock is the ptfe tubing: the long tube & the heatbreak tube are capricorn XS. The extruder steps and the linear advance are both calibrated. The heatbreak tube was quite tricky to make (using tools from printables): it requires a literally razor sharp blade to chamfer and remove any blur. By the way, it is easy to over-compress it: in this case the filament does not move freely (it requires some force) which leads to under-extrusion during small perimeters and start of infill, so be extremely careful when you replace it!
I have printed a lot with these settings and the only strings produced are when arachne uses a large perimeter width (~0.6mm). I guess it adds pressure in the nozzle that linear advance cannot compensate. And the filament is probably not that dry (two years old), even if it was stored in a vacuum sealed bag when not used for a long time. Using the same settings (except LA) and a cheaper but drier filament, there is almost no strings at all and the nozzle does not leak at the end of the print. I can even pause the print for minutes without any leak, and print at a higher speed. If the classic perimeters generator is used instead of arachne, it is a stringing nightmare!
The linear advance calibration shows also something interesting: it is quite constant for this prusament (K=0.36) for each temperature and layer height tried. That is not the case for the cheaper filament.
Can someone explain these settings?
I think that by adding more retraction, it stretches the filament which leaves some place for air (or water from the moist inside the filament) to expand and add pressure. And with a lower temperature, there is more viscosity and the small strings do not break as easily and are stretched on a visible distance when the nozzle moves.
What are your experiences to reduce stringing?
Obviously, it is to dry the filament. But what is your well proven way to do it? I am looking at the filadryer S2, but it is quite pricey and I don't know it's worth it. Thanks for sharing tips!
RE: Counter-intuitive way to reduce stringing
The MINI is doing a long print since this morning, with a lot of 0.6mm filling at every layer, producing some small strings. I've augmented the nozzle temperature to 215°C mid-print and it is way better... this is really weird.
Is this really the way to go?
The *first* thing to try with stringing and oozing is - drying the filament.
It can take only a few hours to begin stringing in humid atmospheres.
Cheerio,
RE: Counter-intuitive way to reduce stringing
You're so wright about this! But I don't have a drier for the moment and I need to print something... I have to print... I must print!
I've printed some big things to use all the external layer of the spool, hopping the core layers are driers. It looks like it was effectively the case: the MINI is now printing a lot of small parts with a lot of retractions, and it is looking great (still using 1mm of retraction, and 215°C for the nozzle; the colour is actually really nice!).
I've found out that it is even better (and so much quieter!) by setting the print fan at 20% in prusaslicer (except for bridging). Why is it set at 100% by default? I think I'm missing something.
By the way Diem, do you have a dryer system to recommend? Thanks!
RE:
People have been able to get food dryers to do the job. I for one am a happy multi-year customer of the PrintDry Pro system. I've not heard anything bad about it (aside from the $$&), unlike the Sunlu dryers where opinions seem mixed.
do you have a dryer system to recommend?
I just use a modified food dehydrator:
I didn't do much research - just picked one that used up the remaining credit on a gift-card.
You can either snip out the bottom of a couple of trays to make room for a filament roll or do what I did and print a tall spacer. A translucent PETG spacer has worked OK for me so far...
Attached are files for the spacer.
dryerinsert should fit a Mini, print three and glue together to make a spacer.
dryerinsert1 fits an i3, print two and glue together.
Cheerio,
RE: Counter-intuitive way to reduce stringing
Thanks for your answers, both of you! I've finally bought a filadryer S2: it is ready to use out of the box, dead silent, and does the job well!
Using it, I 've been able to revive a two years old PETG spool. Two years ago, I gave up on this one just after very few prints, because the quality was quite horrible, even if it was a brand new prusament. After one day and half in the drier, the RH have gone from 48% to 18%. After the LA calibration, the prints are perfect, and printing PETG is so easy that I think I'll buy more spools now. But from this experience two years ago, it looks like the spools have to be dried even when new (or was it a bad batch?).
Anyway, the drier makes the prints so easier that I wonder why there's not already a `prusa drier' in the prusa family.
RE: Counter-intuitive way to reduce stringing
it looks like the spools have to be dried even when new
Just because it's new doesn't mean it didn't sit on the shelves of a distributor for many months. And I for one don't think these vacuum sealed bags hold up too well. I don't routinely dry new spools but I have seen enough that after the first print clearly showed me they wanted to go into the filament dryer.
RE: Counter-intuitive way to reduce stringing
Just because it's new doesn't mean it didn't sit on the shelves of a distributor for many months.
For prusament, there is the fabrication date on the box (and a dessicant in the vacuum sealed box). But it means nothing if bad things happened beforehand. From what I know, only Overture communicates on selling dried fillaments, which makes me thinks the initial RH is quite variable for the other brands.