MK4 PLA Stringing  

RE: MK4 PLA Stringing

Please keep us updated.

I'm waiting for the XL thermistor now, after Prusa sent me another MK4 thermistor which behaves better, but I still need to lower temp in my slicer by ~ 20degree (it was 35-40 before) so definitely thermistor issue in my case. 

RE: MK4 PLA Stringing

Hello!

I too have a problem with PLA printing with the presets. Hard stringing, no forgiveness. I measured the thermistor with the black wire. At 22-23 degrees celsius in my room it read 107.5 kilohms. I'm not sure, but at 25 degrees ambient it should read 100 kilos of resistance. In short, it might be working properly. My question is if so why is the "Prusament PLA" profile set with similar print temperatures. I've been doing tests for a few hours today and I've come to the conclusion that I need to print at 210 temperature on the first layer and 200 for the others. In addition, I also include several settings in slatzer 2.7.0 version, expert mode. So the settings that improved the quality dramatically and there is almost no stringing, 97% less (a few hairs that are microns and break with a gentle touch):

PRINTER SETTINGS/ EXTRUDER-1/

TRAVEL LIFT

Use ramping lift-On

RETRACTION

Retract on layer change- On

Wipe while retracting- On

There are no other changes. Now I'm also completing a test at 190 degrees with the same settings. H is 70% done and there is only one hair to thread! I don't post pictures because the work is clear.

  Do I need to contact support to request a new thermistor from "XL" or work on 180-200 for PLA?

No one talks about the other filaments. For example PETG, PC, ASA, ABS. How will printing with these filaments be affected with the wrong thermistor?

Please help! I gave my 5 cents on the threading thing. My printer is MK4 Kit. 🍻 

RE: MK4 PLA Stringing

Have been having loads of stringing on my MK4 kit build. Just got the replacement XL thermistor yesterday and at best it's a mild improvement but still way too much stringing. Opened a new spool of Silk PLA and left it in a dryer for 12 hours and still extremely stringy.

Tried some retraction tests with Orca slicer and looked hopeful but going back to a proper print and it still the same stringing after adjusting the retraction length. Have also tried ramping, retract on layer change and wiping and no change.

Got this kit about a month ago now and it's really quite tiring getting nowhere fast, had a faulty mainboard, replaced that and fixed that issue but no luck on the stringing.

Are there any other things with the hardware that is worth looking into regarding this?

RE: MK4 PLA Stringing

In my case all the filaments require 30-40 degrees less than the standard profile for them. For PETG I had to use ~ 200degree so it prints good... 180-185 for PLA. Looks like a bad thermistor for you as well... 

I was thinking at the resistance measurement at room temp, 100K at 25degree... That's just a rough ideea if the sensor is good or not, but can't know for sure. It may have correct resistance at 25degree, but the resistance curve may be completely wrong.... so when reaching let's say 200degree it can have wrong resistance, therefore is heating more when it shouldn't... That's what I think it happens...

RE: MK4 PLA Stringing

Still, I didn't understand once we have PLA strings, what happens with PETG printing? Do we have to lower the nozzle temperature there as well? And last question how do I contact the troubleshooting department? I also want a "Prusa XL" thermistor. I think è my warranty covers such defects.

Thank you!

RE: MK4 PLA Stringing

The prusashop page and other prusa pageshave a chat window which appears at the lower right corner of the page after a couple of seconds. That is the support team. 

RE: MK4 PLA Stringing

Posted by: @mariadumitruiulian

Please keep us updated.

I'm waiting for the XL thermistor now, after Prusa sent me another MK4 thermistor which behaves better, but I still need to lower temp in my slicer by ~ 20degree (it was 35-40 before) so definitely thermistor issue in my case. 

Did you mean me? I haven't got around to the final testing yet. I did a 20 hour print for two small detailed christmas ornaments with the 0.25 mm nozzle assembly and set temps to 180 for first layer and 170 for other layers. Then later during printing I heard some squeaking that I thought may be the extruder and increased back to 175 in the tune menu. Print came out great.

Also I had noticed some people said that the thermistors having the issues seemed to have black wires, and the ones that did not had blue wires? Did I remember that correctly? The other day I noticed the thermistor I got with my MK4 in July had blue wires. The two other thermistors I got in Nov, one of which is on the 0.25 mm nozzle assembly and had major stringing issues, both had black wires.

RE: MK4 PLA Stringing

I have just finished 6 hours of printing the elements for the bottom part of the "Ikea" Enclosure and I think there is no stringing on PETG. I haven't tested on a tower model.

   Do you lower the temperature when printing with PETG? Or do the thermistor problems only apply to the PLA filaments? I only use Prusament for now.

RE: MK4 PLA Stringing

I switched to trying PETG last night, have some Prusament Matte Black PETG, I had been holding off using until I had PLA working well. I dried the PETG in a Sunlu 2 at 65c for 12 hours, then rotated the spool and dried for another 6 hours.

Started with a temp tower and to be honest none of it looked good but at 220 bridging failed and the nozzle knocked the print over. Started another at 220 to 200 and it immediately did the same, so I figured 220 really is too low.

Did a real print on a small simple object starting at 225, it looked nice on the walls but infill had gaps/missing bits, upped temp to 230 the infill improved a bit, went up to 240 and the infill was fixed, coming out nice however first sign of stringing when retracting at layer change, dropped temp to 235 to finish and looked ok.

Started a bigger print that nearly maxed the build plate but only about 15mm tall, Prusament Matte Black PETG at 235 and it came out beautiful, a couple strands that is typical with petg that brushed off easily, consistent colour tone on the walls, the least amount of ringing I have seen on this part and I have printed this on Bambu/Anker/Elegoo printers before as comparison, this print on the MK4 is the nicest I have printed so far. Unfortunately I was asleep during this print so did not see how the inside/infill went down but I'd guess it went ok.

Used the textured plate for this, first small print it lifted in one corner but washed the plate and the overnight print had no issue.

Some more details, my original thermistor was the black one, at room temp it actually read quite normal at 101.2 I think, I have not tested the new XL thermistor with the multimeter yet though.

Now I need to sort PLA still however I think after the testing with PETG it tells me the nozzle temp is probably reading fairly correctly. I have another PETG print going and will continue to test PLA and hopefully figure that out too. The Silk PLA I use is Eryone and Gratkit brands in case anyone knows good profiles to use for those, please let me know.

RE: MK4 PLA Stringing

Been watching this thread for the last couple weeks. Just chatted with support and will be receiving a new thermistor as well. All they asked for was one photo of the hotend. Previously measured my thermistor resistance at 89.9k. Only way to print is between 170 and 175. Looking forward to the replacement and will measure it before installation.

RE: MK4 PLA Stringing

Current status: On third thermisistor (asked for XL one after the initial replacement made no difference). Printed test piece much better, then I printed https://www.printables.com/model/258049-the-benchy-cali-trailer and it looks great (see pics), so am calling this good!

RE: MK4 PLA Stringing

In my opinion, there is still a lot of stringing. I’m sure it has gotten better with the right thermistor, but there should be absolutely none.

What do you guys think about it?

RE: MK4 PLA Stringing

I can confirm that changing to XL thermistor fixed my printer, and I can now print with default profiles temperatures. I initially received another MK4 one as replacement which improved but not fixed the issue. Went back to support and they sent XL, and now it looks like my issue is fixed and I can finally print with the default temperatures ... Happy days! Btw, new thermistor measuring ~ 134kohm at 18degrees.

RE:

I think I have the same bad thermistor on my MK4 that others here have experienced, it's been causing stringing and bad bridges for months.  I tried doing a stringing test and reducing the temperature until it worked... a full 30 deg C lower than the stock prusament pla profile and stringing disappeared:

This is with the stock input shaper 0.15mm speed profile and my 0.4mm stock nozzle.  I've been printing at these lower temperatures and the parts look great with no stringing so far.  I'll try to contact support and request a new XL thermistor soon, when it arrives I'll see if I can compare temperatures to a thermocouple while heating. 

RE: MK4 PLA Stringing

Guys I finally found a fix! I returned the printer. After wasting countless hours and beyond useless support I returned it. They did not pay for return shipping but that’s better than living with a defective product; Lesson learned. I’m done with Prusa, from here on out I’m just building Vorons. To those of you past your return date I wish you luck!

RE: MK4 PLA Stringing

Those are nowhere near as "bad stringing" that other folks were getting. Here a pic of my "pre XL thermistor" tests (at 215 and 195). I do still lower the temps with the XL thermistor and my usual PLA, but then I've always found the Prusa Slicer / default settings a bit high

RE: MK4 PLA Stringing

I'm experiencing the same stringing issues as described in this thread, and after some obligatory troubleshooting with the live chat agents, they have sent me a replacement hot-end thermistor (the one from the XL as suggested earlier). Should be arriving on the 29th, so I'll fit it and share my findings.

Quick question though; after fitting the new thermistor, will I have to do any PID tuning? If so, how do I do it on the Mk4?

RE: MK4 PLA Stringing

Thermistor hasn't arrived yet, but I figured I'd do some detective work in the meantime.

Looking earlier in the thread, I can see people have taken resistance measurements from their thermistors and reported them being quite far off. I've taken a measurement, and at 19C it's reading between 70 and 80k, when it should be reading somewhere in the region of 110k.

I've just been talking to a support tech through the live chat and they sent across the specs of the thermistor:

15°C → 161.7 kOhm
20°C → 126.8 kOhm
25°C → 100 kOhm
30°C → 79.3 kOhm
60°C → 22.5 kOhm
100°C → 5.5 kOhm

So yeah, safe to say the thermistor is faulty. Fingers crossed the XL one will work for me.

RE: MK4 PLA Stringing

Been doing some more prints with the new thermistor and find PETG is not as bad, though quite a bit of blobs and strings around the seams.

Going back to PLA and it's still really bad, I did the same print with same spool of filament on Bambu A1 Mini and it was way less stringy so I do not think it's a filament moisture issue (I had dried the filament anyway)

I took some new readings with the multimeter and my original Thermistor at room temp was 105.5 and the new XL thermistor is reading 71.2, so I'm thinking the XL thermistor is not right either.

I will contact support later and see what to try next, I really want to get this sorted as beyond this issue I can see the potential in this printer.

Has anyone else had any recent success? The only somewhat success I have had was using Cura with the default MK3 profile as there is no MK4 option, although it printed the purge line in mid air it then did the print and it had quite a bit less stringing however the print quality on walls seems worse. I tried to copy over the retraction settings from Cura to Prusa but they didn't improve things.

RE: MK4 PLA Stringing

Welp, nothing-burger of the century.

Took delivery of the new thermistor today and measured it versus the one that is currently fitted. Gave the same ~70k reading. All of my readings so far have been at the 200k setting on my meter which is ostensibly the correct one to use, but switching over to the 2M setting, both were reading 110k.

Hmm.

Borrowed a multimeter from a neighbour who does his own maintenance on his car, double checked my readings, aaaaaand...

Both read ~125kOhm at ~20 degrees, pretty much exactly in line with the datasheet. So my meter is garbage and is going in the bin. Sorry for the anticlimax. Time to pursue other troubleshooting avenues.