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poor print quality after cold pull & tune up  

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prolix21
(@prolix21)
Eminent Member
poor print quality after cold pull & tune up
I started having issues the other day with what seemed like under-extrusion, and then at some point the nozzle clogged and nothing would print. First layers would print ok, but then got stringy and eventually just seemed like no extrusion at all was happening. This was very sudden, and after a couple weeks of flawless printing.
I read through the forums and found a number of posts and articles about cold pulls and under-extrusion, so I did the following - 
1 - Performed a number of cold pulls until the clog was cleared and bottom of the heat break was totally clean/clear - I followed - https://help.prusa3d.com/en/guide/how-to-change-a-hotend-ptfe-tube-mini_119449&source=gmail&ust=1610328111556000&usg=AFQjCNGOIfGdLL9h6SLB542J27XrNO44h g"> https://help.prusa3d.com/en/guide/how-to-change-a-hotend-ptfe-tube-mini_119449 to make sure the heat block was correct and the hotend PFTE was compressed correctly. It did seem like the hotend PFTE was not in correctly / the heat block wasn't seated right
2 -I also took apart and cleaned the extruder pulley, as there was a lot of debris in there.
3 - Because I raised the heat block I had to reset the MINDA sensor height and re-ran the live-z which all went fine as well

I also ran one of the needles through the nozzle itself and it seemed clean, and if you purge it all comes out smoothly

All tests pass ok, re-did the live-z calibration, which prints fine, looks like any other calibration I've done.
 
When I print, the results are pretty bad compared to before I started.
 
Before, everything was smooth, no stringing, all print passes looked complete. 
After, the first layers all print ok, but subsequent layers start looking thing, stringy and a bit incomplete in spots. Just really inconsistent.
 
This happens no matter what brand of PLA I use - I've mostly been printing with prusament PLA and then the other PLA prusa sells. 

These are also using the same gcode files I used before, so I don't think its the file. They all printed fine before the first big clog

 
I've followed every KB I can find regarding clogs, cold-pulls, other posts I've seen here about the heat block and hotend PFTE and the machine itself seems like it is all setup right - extrusion gears totally clean, tension set right, everything feeds great, purges ok, can unl0ad and re-load fine without any issues (couldn't do this before).

Posted : 10/01/2021 1:30 am
Alex Hung
(@alex-hung)
Trusted Member
RE: poor print quality after cold pull & tune up

Not saying this is the cause, but how humid is your environment? I noticed that most of my failed prints are due to humidity or filament that has been left out for a few days.

Posted : 10/01/2021 4:03 am
prolix21
(@prolix21)
Eminent Member
Topic starter answered:
RE: poor print quality after cold pull & tune up

Very low humidity here - after I posted this I was reading the "Hardware, firmware and software help" section and started find a lot of similar issues with shrinking PFTE tubes, clogs and other issues which I think is still what I am running into.  I may take the entire hot end apart again and double-check it all. Seems like a lot of people in the other section are having the same issues repeatedly with their units. 
 

Posted : 10/01/2021 4:18 am
Alex Hung
(@alex-hung)
Trusted Member
RE: poor print quality after cold pull & tune up

Yes I notice too. At the same time, I am sure there plenty of owners who have no issue. I had one clog and after I pushed the heater block up against the PTFE tube, the problem went away. That was like 3 months ago and have been printing without issue until the rain season hit us 3 weeks ago and humidity went up. That caused a partial clog that was resolved quickly. And I have zero problem since then. 

Posted : 10/01/2021 4:25 am
prolix21
(@prolix21)
Eminent Member
Topic starter answered:
RE: poor print quality after cold pull & tune up

@alex-hung

That is good to know - I am going to loosen up the heater block again and replace the PTFE tube with the spare, I think I still have some sort of issue going on with that heatblock. Will post an update when I rebuild that tomorrow. 

Posted : 10/01/2021 4:37 am
prolix21
(@prolix21)
Eminent Member
Topic starter answered:
RE: poor print quality after cold pull & tune up

Just a quick update to this - did another rebuild of the hot-end and we're back in biz - I ended up replacing the heat-break, PTFE tube and nozzle just to clear any clogs I couldn't see/figure out and everything seems good. I did end up switching to the Bontech heat-break just to be safe, since I don't feel like having to take this apart again anytime soon

Posted : 16/01/2021 9:04 pm
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