MK4 PLA Stringing  

RE: MK4 PLA Stringing

Checked the resistance ... 75. Contacted support they are sending me a new thermistor. Didn't mention anything about the XL one. 

Let's see how it goes. 

RE: MK4 PLA Stringing

I'm having the exact same issue sadly. I've already ordered another thermistor in the hopes of fixing it. I did measure the resistance at room temperature and it seems to be around 112 kOhms at room temperature.

Interestingly enough, the heater self test does fail and I can't get it to succeed. Since this is my first printer, I have nothing to compare it to sadly except the results shared in here.

RE: MK4 PLA Stringing

hello everyone,

I also received the new thermistor.

I immediately printed a temperature tower and it was perfect, but then I tried to print a string test with the default values for the pla prusament and the result was not perfect... better than with the first thermistor but not perfect.

So I tried lowering the temperature and noticed that around 200 degrees the strings disappeared completely, also with other string tests. (see the photos, the prints without strings are printed at 200 degrees)

I also enabled "use ramping lift" and "wipe while retracting" in the printer setting and they seem to help.

RE: MK4 PLA Stringing

I got my new thermistor on Friday. 
It looks as well like an XL thermistor (115mm and black wires with the orange shrinking tube).

I compared resistance it with my old one (blue wires) before changing (17.5 degrees room temperature):
Old: 142.9 kOhms
New: 144.5 kOhms

I did a testprint before and after the change. There was almost no change.

Before:

After:

I tried then with some new filament (Galaxy Black) with my old stringing test and it turned out almost perfect:

So I really don't know for the moment if it was just the Marble Prusament or if the first stringing test was to hard to handle. 
I'll investigate it further or does anybody have an idea?

RE: MK4 PLA Stringing

In your case looks like moisture or filament itself may be the problem...

I see most people with thermistor problem are reading well below 100Kohm, like 70-80 , and will have this problem with any filament. Your printing turns out OK after filament change, so try to dry your filament and see how it goes...

RE: MK4 PLA Stringing

Can someone give me a brief description of how to measure the resistance associated with the thermistor? Do I have to remove it to make this test, or can it be done in-place? Really appreciate your help on this - thanks!

RE: MK4 PLA Stringing

Ideally we should disconnect it from the breakout board. It should read 100k ohms at 25centigrade.

Slightly higher at lower temperature.

RE: MK4 PLA Stringing

For me the problem is almost gone after installing the XL thermistor.

Wrong batch, shame it took so long.

RE: MK4 PLA Stringing

Hi everyone,

I've experienced the exact same problem: thin stringing on every prints with my new Mk4 (kit). It was independant of the nozzle temperature, retraction speed and distance, wiping, dried or not filament (new or old), no stringing on my Mini+ (with input Shapers) with the same filaments and the same parts. I measure the thermistor and the value is ok (~103Ω at 20°C), so it seems it's not a temperature relative problem.

But there is hope! I enable Ramping lift on PrusaSlicer 2.7.0 (settings - Extruder - Travel lift - Use ramping lift), set Both height and angle to 0 (original values). And the stringing is gone !

You can improve even more by activating wiping. And with stock speed and retraction settings. I don't know why Ramping Lift is not activated by default, it's the case on the XL.

I hope this will work for some with thin stringing issue and recomand to try this setting first before investigate the thermistor side !

Enjoy

RE: MK4 PLA Stringing

*Correction: 123Ω at ~20°C

RE: MK4 PLA Stringing

Got my XL thermistor (blue wires with orange heat shrink) and tested resistance at 98 kOhms, so it should be good to go. I'm in the middle of print but will swap it out after and see what happens. 🤞

RE: MK4 PLA Stringing

Got my XL thermistor (blue wires with orange heat shrink) and tested resistance at 98 kOhms, so it should be good to go. I'm in the middle of print but will swap it out after and see what happens. 🤞

RE: MK4 PLA Stringing

Just got my thermistor today, it's a MK4 one, with black wires (not the XL with orange heat shrink), measured at room temp at about 18 degrees shows 134Kohm... In the middle of a print right now, will change later on and test... Fingers crossed ... 

RE: MK4 PLA Stringing

Stringing is 90-95% gone at 210° with the new thermistor! I wish I would have done a temp tower with the MK3 so I could really do a before and after comparison...

RE: MK4 PLA Stringing

Actual image:

RE: MK4 PLA Stringing

Support sent me a new thermistor and I just received it and check both the old and new one at room temperature, old one was 112K Ohms, while the new one was 107.5 K Ohms.  The thermistor they sent me looked just like the old, black wires and same length but the bag was labeled Hotend thermistor NTC 100K - 90 mm. What I did find interesting is when I went back to the stock PLA profile which uses 230 for 1st layer and 220 after that, while on the 1st layer it was calling for 230 but it only got to around 220.

Thanks Ray

RE: MK4 PLA Stringing

I got and replaced the new thermistor as well, I received the same MK4 one, not the blue with orange heatshrink. When I changed I measured both at room temperature and both showed 125-130 kohm(new one few kohms higher)(not 70-80 like other ones I've seen here.). However I changed it and print looks better,

I wonder if my problem is solved. See image below, with old thermistor vs new. Also the keychain that is already on the usb stick, with default settings (IS 230 first layer and 220 after) looks pretty decent, first layer looks good, printing has small bit stringing.

What do you think?

RE: MK4 PLA Stringing

With the results other are getting with the XL thermistor, I contacted Prusa to get a replacement for mine. The last straw for me is when I ejected some filament and smoke poured out the nozzle. This was not steam since I dry my filament. It was a filament the I was having to go down to 180c to print with and still had some stringing and the 215c was much too hot to eject it. I am hoping this will finally fix this problem, if not I still have a couple of Triangle Lab thermistors in the mail here that I can try.

RE:

@mariadumitruiulian

Exactly the same with me. Got the replacement thermistors which definitely measure correctly at 20°C and 220°C according to the data sheet of the sensor which is specified in the Firmware (104NT-4-R025H42G). Still a lot of fine stringing. Both of my other printers (X1C and Neptune 3 Pro) are printing perfectly fine at the same temperatures with the same filament. I'm not willing to accept this for a 1000€ printer. My MK4 is currently on its way back to Prusa for further investigations.

RE: MK4 PLA Stringing

Hey all. I had a printer I had in July, no stringing issues. Occasionally some wisps and such. Then I got a 0.25 and 0.8 mm nozzles last month. I got heater blocks and thermistors too, to have entire assemblies and swap the nozzle assemblies rather than the nozzles.

Tried printing a mini with the 0.25 mm nozzle and it was…terrible. So much stringing. Like the stringing tests here.

I did some testing and it seemed the thermistor was ~100 k at 25 °C. Hot side I didn’t have a data sheet but found a spreadsheet and it seemed close, but I really need a data sheet. 331 ohms at 209 °C:

Meter on right is reading temp with a thermocouple on the side of the heaterblock, meter on left is reading thermistor resistance. Power supply was used for hot test to power the heater. Hot test current on supply was limited until the temp change was minimal (steady state, or very close to).

I found this thread and that spurred the testing above. When nothing obvious jumped out, I downloaded a stringing test and ran that. I think it shows a thermistor issue:

On the left is printed with IS defaults, 0.4 mm nozzle, 0.2 mm layer height, STRUCTURAL preset. On the right is IS defaults, 0.25 mm nozzle, 0.12 mm layer height, STRUCTURAL. Middle is same as right only bottom is 220 °C, then it goes 210, 200, 190, 180, 170, changing at each notch.

Seems pretty clear the issue has to be the thermistor in my 0.25 mm nozzle assembly, which again was bought about a month ago.

One last test I’d like to do is put the 0.25 mm nozzle in the 0.4 mm nozzle assembly, since this assembly had been printing 0.4 mm nozzle since I got the printer in July. If the stringing test is good, then that conclusively shows the thermistor I got for the 0.25 mm nozzle assembly is bad. Which also lines up with the timeframe of posters here getting bad thermistors with their printers, which makes sense.

My 0.8 mm nozzle prints okay, but if this has an issue I suspect that thermistor also has an issue. It did seem like it had a lot of oozing when I printed with the 0.8, but I thought it was just the bigger nozzle. Now I think it’s the thermistor.