Sudden issue printing with 0.8mm nozzle

[JonGregory 0]

Hello all - I've been happily printing stuff for a while now and wanted to print some larger things so swapped the 0.4mm nozzle for a new 0.8mm one. And whilst I expected the print quality to suffer a little, I didn't expect it to dive off a cliff and leave the building. It seems as though the nozzle is over-extruding or over running and pushing the outer wall which then frills out and causes a ridge which is higher than the next layer resulting in a progressively worse clash between the nozzle and part. The only other thing that has changed in my process is the version of Cura (now 4.6) - I've tried resetting all of the profile tweaks I've made over the months in case something I've set has caused it - but with no change. I've also tried a range of temperatures and initial layer heights. Noting seems to fix the problem.

 

So, has anyone seen this / have any suggestions?

 

Cheers

[JonGregory 0]

Well, I've made some progress and got much better results - not great, but much better. When I was printing with 0.4mm nozzles (PETG) I often turned the cooling down to zero to get the material to flow together a bit better - it seems that this isn't a great idea when printing with 0.8mm nozzles. Maybe the thermal mass of the fresh layer is a bit greater (although it's the same thickness) anyway, it seems that the nozzle picks up on the layer too easily and causes that frilling effect. Turning up the cooling flow to 75% cured most of the problems. Slowing down the print from 60 to 50mm/s also helped (it is laying down four times the volume than 0.4mm nozzles at the same speed after all). I also reverted to a hotter baseplate (85DegC) and my preferred setting of a super-slow initial layer or two (10mm/s). I then switched to 40% infill (Gyroid for a laugh) and increased the outer wall thickness to 2.4mm or 3 wall passes - the overhangs are still a bit rough and the surface feels more like paper than the silky smooth plastic feel I usually get - put the part is functional at least.