Terrible Stringing Problem
I've been printing with my Mk2S for well over 2 years and have created some great prints. But lately stringing has become increasingly worse. The attached photo shows my latest attempt to print an enclosure. I've tried this with 2 different brands of PLA filament. I've always printed PLA at about 215 - 225, but I've been reducing that to help solve the stringing problem. This enclosure was printed at 195, with 1.5mm retraction, 0.2mm layer height, 3 perimeters. Most other settings are at their defaults. I dried the filament in the oven at about 135 for about 4 hours before printing. I'm wondering if the thermistor is bad and giving false readings, so the hot end is hotter than it should be. Any suggestions?
Thanks,
Rich
RE: Terrible Stringing Problem
If you put PLA in an oven at 135c you have annealed it. PLA seldom needs drying but when it does 45c is a normal drying temperature. Try with a new fresh roll of PLA and do a temperature tower for the new filament before you start printing.
Bill
Tagaytay City, Philippines
Founder member of Philippines Prusa Printer Owners FB Group
Sponsor Pillars of God Academy in Bacoor
RE: Terrible Stringing Problem
Seems like way too much retraction. Try something closer to 0.4 mm ... with a touch faster retract speed.
RE: Terrible Stringing Problem
Thanks for the input guys...I appreciate it! I should have been more thorough with my original post. I dried the PLA at 135F, not 135C, so that's about 57C. That's just an estimate, but the oven won't go much lower than that.
I tried 1.5mm retraction to try to solve the retraction problem. I was having problems with the default setting of 0.8mm, so after doing some research I learned that increasing retraction can improve stringing so I went to 1.5mm.
Actually, I have had some success lowering the temperature even farther. I just printed the same box at 180 and had just a little stringing. And I've found that different filaments string differently. But up until recently I could print at 215 - 225 with no stringing problems at all, so I think there is something wrong with the extruder. I'm really thinking that the thermistor is giving false readings and the hot end is considerably hatter than it thinks it is. I'm considering ordering the Mk2S to Mk2.5S upgrade kit, partially to try to solve this stringing problem, but also because there are some cool new features included. Thoughts?
Thanks!
Rich
RE: Terrible Stringing Problem
I did some experimentation and found I got identical results with retraction distance set to 0.3-4mm as going higher. Try reducing retraction and z-lift distances. Filaments do vary, but if you're seeing a big change from prior results, consider swapping your nozzle. I stoically stuck with my original brass nozzle until I realized I got much cleaner results after swapping it out. Does the Mk2 offer the PID and bed temp calibration routines? Might be worth repeating those.
RE: Terrible Stringing Problem
I don't have this resolved yet, but I have found that drying the PLA for several hours does practically eliminate the stringing. I know this shouldn't be necessary for PLA so I'm still searching for an answer. I bought a new nozzle but have not yet replaced it.
But now there is another symptom...the hot end won't cool down (according to the display). I didn't know if this was related to the stringing problem so I started a new thread: https://forum.prusa3d.com/forum/original-prusa-i3-mk2-s-general-discussion-announcements-and-releases/hot-end-wont-cool-down/
Rich