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PETG first layer blobbing and crashing  

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Odin
 Odin
(@odin-3)
Member
PETG first layer blobbing and crashing

I recently replaced the hotend of my MK3S. After two successful prints, the printer is having issues. It begins the first layer but drops a few blobs around that eventually build up and cause a crash when colliding with extruder nozzle. Images below show what I mean.

I was pausing the printer and manually snipping blobs and peelings off so that it would print properly but I cant do this for 10+ hour prints. It is dropping blobs constantly.

I've done the following:

- Dissembled and re-assembled extruder twice to make sure everything is correct and tightly bolted.

- Run Calibrate XYZ , mesh bed levelling and first layer Z calibration numerous times. The first layer calibration I have tried a range of heights.

Regardless it keeps making these blobby peely prints in random areas. Note that most of the print is fine and cleanly made, and that these occur randomly but 2-3 times per layer. What is causing this?

 

Posted : 28/01/2024 4:01 pm
Brian
(@brian-12)
Estimable Member
RE: PETG first layer blobbing and crashing

Has your petg been dried? Petg oozes a bunch already, and if it's wet it'll be worse.  

Have you measured the filament your using and entered those values into PS?  Over extruding can cause I blob of filament to build up on the nozzle and randomly drop off on the print.  This is especially prominent on the first layer since we're squeezing that layer already. 

Your print bed might not be very flat either.  Auto bed leveling will only do so much.  I recently leveled mine using the nylock method and the first layers have improved significantly. 

Posted : 28/01/2024 8:26 pm
Odin
 Odin
(@odin-3)
Member
Topic starter answered:
RE:

Im using hatchbox PETG, in fact this is my 4th spool of the exact same PETG. In the last month ive done 12+ large prints with no issue whatsoever so I dont think the filament is the issue (To be sure I tested the remains of the 2nd and 3rd spool to which blobs still occur).

I've adjusted the first layer z height and found a very good sweet spot. In terms of bed leveling, I ran the bed level correction print  and got a perfect result (no blobs). I thought the issue was resolved, low and behold trying to run another print and 20 minutes into it a blob has appeared and has caused the print to crash and fail. So they are less common now but will definitely occur in a 10 hour print that will ruin the entire thing.

 

What do you mean by over-extruding. I've been using the same extruder settings as my previous prints of the same filament which worked. How can i reduce this then to help now?

 

NOTE: I've noticed the heater block becomes loose when heated. When it is cool, it's firmly bolted with the heatbreak and rest of the hotend and doesnt move but when heated it can move around slightly and turn around the heatbreak. Could this be the issue and if so how do I fix this?

 

This post was modified 3 months ago 2 times by Odin
Posted : 28/01/2024 11:42 pm
Diem
 Diem
(@diem)
Illustrious Member

When changing, did you pay particular attention to the diagrams at the bottom of this page?

https://help.prusa3d.com/en/article/changing-or-replacing-the-nozzle-mk2-5s-mk3s-mk3s_2069

Cheerio,

Posted : 29/01/2024 1:42 am
Brian
(@brian-12)
Estimable Member
RE: PETG first layer blobbing and crashing

If it was never an issue before you changed your hot end then it's got to be something related to the install of your new one.

Over extruding is when you extrude too much plastic. But if you've changed no settings and it worked before you changed the hotend, then it's likely not a settings issue. 

Posted : 29/01/2024 10:58 pm
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