PETG large print disaster  

The warp pattern on the top is a giveaway.

Either the first layer has partially detached in which case all the usual advice about adhesion applies or the adhesion was good but the print sheet itself lifted off the magnets under strong tension.

Most of the tension comes from thermal contraction as the longer extrusions cool. 

The Core One should have protected the print surface from drafts but if you had the door open try again closed ... and perhaps raise the bed temperature by 5° - 10°.

but the underlying problem is better addressed by breaking the long extrusion runs: 

    Use a fill that does not have long extrusions, honeycomb, gyroid or similar.

    Reduce the number of horizontal layers on the top, perhaps put some 'decorative' grooves in the top.

In extremes even clamp the print-sheet down to prevent lifting.

The breaking filament is unusual for PETG although a known issue for damp PLA.

Remove the lid, open the extruder idler,  detach the PTFE filament tube and heat the hotend to the printing temperature of the filament plus 5° then take a length of scrap filament and, bypassing the extruder gear, push it down through the nozzle tube by hand — push slowly at first then as fast as it will go finishing by pulling it out as fast as you can.

You may need to temporarily disable some sensors while you do this.

Cheerio,

RE: PETG large print disaster

Hi Diem

Thanks for your answer. I will go with a different fill and fewer top layers. I had extra top layers for strength, so that's a good candidate for the issue.

I've taken the hotend out and am using a craft hot gun - and an oven mitt. What you propose would 'glue' the stuck bit to the extra filament I guess, I will give that a go. Wish me luck.

Thanks again for your reply.

(btw. just for reference if anybody is interested: what I forgot to mention  in my 'state of frustration' was that I am using the Core One - which you already mentioned- with the slicer v2.9.3RC1)

RE:

When clearing the stuck filament, don't be afraid to use higher temps. 25c over the print temp may help get the cooked gunk out of the nozzle. And, the printer comes with a needle to insert up the nozzle. That can also dislodge stuck filament. Not sure how well they work in a CHT nozzle, but worth a try. PETG isn't as abrasive as some filaments, but probably a good idea to check the nozzle for sandpaper damage ... compare it to a new nozzle and ensure the tip isn't too abraded.

Since you mentioned the sheet was pulled off the magnets, and not the PETG was separated from the sheet ... not much to do there but manage part warp with the heated chamber and infill selection. Let the printer go through the full heat absorption phase and perhaps even raise the temperature of the chamber requirements for your filament. 

Otherwise, +1 to Diem's comments and suggestions.

RE: PETG large print disaster

Hi Tim

Thanks for your reaction. I tried increasing the temp, but I suppose the bit was stuck too far up the nozzle to get hot enough. It did get a bit soft. The solution for me was to remove the nozzle completely, using the craft gun to heat the part wher the stuck bit was and use the 'glue-and-pull' method. Worked like a charm ! 

Nozzle is working again properly. I also chose a different infill (honeycomb), but the model still warped, off the sheet this time. I kept a close eye on things so I could prevent a mess like last time. As for the chamber heating etc., I just let  the Core-one do its thing.