Uniform Stringy Prints
All of a sudden my prints started coming out stringy. I’ve printed some calibration tests but they all come out stringy as well. This is on a Prusa MK2S using PLA with Prusa Slicer and previously Slic3r
I’ve tried: Temperatures ranging from 175 - 215. Retraction lengths up to 5mm. Retraction speeds up to 100 mm/s. Lowering the max print speed. I've replaced the nozzle and diameter settings are correct. The extruder thermistor has been replaced. Tried a different brand of PLA as well as a fresh spool. Reassembled the extruder to check for any major issues.
The issue also seems to affect objects printed from the preloaded SD card. Any help would be great. Thank you.
RE: Uniform Stringy Prints
[...] The issue also seems to affect objects printed from the preloaded SD card. Any help would be great. Thank you.
That's an important bit of information. You've eliminated any slicer settings. I had a similar, although less dramatic problem some months back. I'm understanding you had no problems until recently. Did you experience a jam or any other problems? I did eventually realize that my original brass nozzle had been damaged. I'd experienced a clog and dug around using the acupuncture needle. I've read a number of sources indicating that damage to the edge of the nozzle opening can cause a bit of excess oozing that can cause a similar problem. A swap cleaned up the worst of my oozing problems. That might explain both the sudden change and previously-fine gcode prints showing this stringing. Can you swap the nozzle for a fresh one?
If you haven't done it before, read up on the procedure. Be sure to brace the heater block, ideally using a 16mm open wrench/spanner and use a 6mm socket on the nozzle. Do the change at 285C. Don't over-tighten but be sure the new nozzle is firmly pressed against the heatbreak. There should be a small < 1mm gap between the nozzle and heater block when you're done. Let us know if this is your 1st time doing this and we can provide more info.
As for retraction settings, ignore 90% of the web tips about retraction distances. The Mk3 has a direct drive extruder, and retraction distances over 2mm will make things significantly worse as you'll be pulling molten filament up past the transition zone and into the cool zone of the hotend. After replacing my nozzle and doing some calibration, I'm getting good results with 0.2-0.4mm retraction.
RE: Uniform Stringy Prints
@bobstro
Thank you for the reply. I don't recall a jam right before the issue, but it is possible. I have replaced the nozzle with a brand new one since then and it did not seem to fix the problem. I could always try another just in case. I've wondered that since the stringing seems to be uniform and not random spurts, could it be due to over extrusion? I've had trouble tracking down exactly how to fix that.
RE: Uniform Stringy Prints
There is another thing to check as I found out and it depends on what firmware you are using and does it use Linear Advance 1.5
The models on the SD card were more than likely created using LA 1.0 so would have a K value of about 45.0.
LA1.5 uses K values closer to 1.0 for the same result, using a K of 45.o results in massive stringing problems.
I did exactly the same, used a previously sliced model and got a hairy monster for a print.
Resliced the model with the K value set correctly for my firmware and it came out perfectly.
https://help.prusa3d.com/article/t5w9VsdVai-linear-advanced
Normal people believe that if it ain’t broke, don’t fix it. Engineers believe that if it ain’t broke, it doesn’t have enough features yet.
RE: Uniform Stringy Prints
I replaced the nozzle with a fresh .6mm (what I had on hand) and am still having the same issue. I use the Prusa guide on how to change the nozzle and it seems pretty straight forward (unless I'm just awful at it and don't notice). Both new slices and old slices are having the same issue, but I checked the K value just to be sure. "M900 K{if printer_notes=~/.*PRINTER_HAS_BOWDEN.*/}200{elsif nozzle_diameter[0]==0.6}18{else}30{endif} " I tried one print with that, and one set just as K30. All with stringing.