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Cold pull eval after giant blob clog  

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surfman49
(@surfman49)
Active Member
Cold pull eval after giant blob clog

All,

I'm trying to evaluate a cold pull on my MK3S+ in order to diagnose issues with my recent prints.

Yesterday, I had a bad clog, the type with a giant blob. I monitored the print for the first thirty minutes, but unfortunately the printer ran a while after before I noticed the problem. Luckily, the E3D silicone sock on my hot end helped to contain the mess on the extruder, but the clog stopped the printer from extruding and the gear wore a notch into the filament.

I don't know the exact reason, but I have a feeling that there might have been a partial internal clog that was restricting the filament flow. On recent prints, there seemed to be some sparser areas on the first layers and the bottom of the prints were not completely smooth. Additionally, the blob print also detached from a fresh side of the smooth sheet (almost new).

At the moment, I'm trying to make sure that the extruder is clear after several rounds of cold pulls. I noticed that the notch in my cold pull (marked in red) is common in examples of OK cold pulls that I found online. However, I'm not sure if mine is normal or not because the notch seems kind of rough.

Does this cold pull look OK?

 

Posted : 16/01/2022 6:21 pm
Diem
 Diem
(@diem)
Noble Member

a bad clog, the type with a giant blob

Almost certain to be a first layer adhesion problem.

Show us your first layer Z calibration print and make sure the print-sheet is clean.

Cheerio,

Posted : 16/01/2022 6:33 pm
surfman49
(@surfman49)
Active Member
Topic starter answered:
RE: Cold pull eval after giant blob clog

Thanks for the suggestion, below are a range of Z calibrations trials. These are done on the fresh side of a steel sheet (that has been printed a lot on the reverse). Cleaned with acetone and IPA.

From what I can tell, the calibrations on the left that are closer to the sheet look better (eg. trials 6 through 8).

I'm plan to continue with some additional trials, going closer to the sheet. Curious know if I'm on the right track and how to tell when it's too low.

Posted : 17/01/2022 10:05 pm
surfman49
(@surfman49)
Active Member
Topic starter answered:
RE: Cold pull eval after giant blob clog

So far, I've tested 17 different Z-offset values (progressively lower and closer to the plate). As the nozzle has gone down, I've seen the gaps between the strokes decrease and the surface has become more uniform.

Unless I'm missing something, I haven't noticed any areas where the nozzle has been dragging along the surface yet. When that happens, then I will probably go higher with slightly more precision until the nozzle no longer interferes with the printed surface.

Posted : 18/01/2022 11:03 pm
Bob
 Bob
(@bob-2)
Reputable Member
RE: Cold pull eval after giant blob clog

If I understand your photos you were doing a live z adjust on the rectangle and was going lower and lower as the print printed to the left?

If that's so looking at #12 you have ridges between the lines instead of gaps, this is an indication you've over shot and are a bit too low.  The sheet shouldn't have any gaps or any ridges when you're at the right level.

-Bob

Prusa I3 Mk2 kit upgraded to Mk2.5s, Ender3 with many mods, Prusa Mini kit

Posted : 20/01/2022 11:51 pm
surfman49
(@surfman49)
Active Member
Topic starter answered:
RE: Cold pull eval after giant blob clog

Thanks, actually this reply really helped me. By the time I read it, I was already even lower on test #30. Then, I went back and re-printed #12 and looked closer for the ridges. If you hadn't replied, then I wouldn't have known to do that. From there, I went higher with finer precision and settled on a Z where I didn't notice any gaps or ridges. Not sure if it's perfect, but my failed print has now succeeded with the new Z-value and I'm not seeing corners lifting that happened in past prints. Thanks again!

Posted : 24/01/2022 12:09 am
Bob
 Bob
(@bob-2)
Reputable Member
RE: Cold pull eval after giant blob clog

If you have what seems like a smooth sheet of plastic then you should be good.  It should be durable when you pull against the grain, if you can separate it easily where the lines are parallel to each other then you need to go a little lower.  The back of the sheet should be a mirror of the bed surface, satiny smooth or textured depending on the bed with no obvious lines.

Cheers

-Bob

Prusa I3 Mk2 kit upgraded to Mk2.5s, Ender3 with many mods, Prusa Mini kit

Posted : 24/01/2022 3:41 am
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