i've started printing in petg with pla supports since the support surface finish is so good, but whenever i print round things with tree supports i see what looks like layer shifts. since my printer is a corexy toolchanger and not a bedslinger this behaviour has confounded me until today, when i happened to look at the right time. it seems that the layers of the perimeter are not adhering properly, and as the filament cools it contracts, catches on support material, and pulls the entire ring off of the pla supports. meanwhile on the middle part i see no issues at all.
i don't even know what to call this problem. it's not stringing, it's already extruded plastic that does it. layer adhesion issues maybe? the photo up top is a reconstruction of how this print looked on the bed, since it fell apart the moment i flexed the buildplate.
printer settings
printer: Snapmaker u1, 0.4mm hacdened steel nozzles
filament: eSun PETG Basic black, Snapspeed PLA yellow
print settings: snapmaker orca "optimal" preset with some minor changes (0.16mm layer height, 15% grid infill (meant to change that), automatic tree supports on build plate only, 2 layer raft, and support interface ironing enabled)
petg settings: orcaslicer's "generic petg" preset with some minor modifications (12mm² max volumetric speed, 265°C nozzle temperature, 10mm retraction, pressure advance disabsed to use the calibration value from the machine)
here's a look at the underside of the pieces:
and a closeup of the round part:
as far as i can tell, that's pretty much perfect before it falls apart.
i can still print with the "normal" supports because they come up the sides of the circle, but it feels like a waste of filament. any ideas?
I mean, like you know PETG doesn't bond at all to PLA, so you're almost trying to extrude PETG in a circle mid-air. There's so little friction/adhesion to PLA that the nozzle simply drags the extruded PETG along with it, it's like trying to extrude first layer but with Z-offset set way too high so the extrusion barely squishes against the plate.
My best guess is to try and turn the speed way down and see if it will help...like <50mm/s
Also you could try classic supports. They have more surface area.
well it does bind, just not hard. the surface area of the central piece is enough to make it stick pretty well. it's just these thin parts that are giving me trouble. but yeah, slowing down probably helps.
I would think the perimeter would have a lot of leverage on the center. I have a Snapmaker on the way but haven't printed with different materials yet. There's like 50 trees around the perimeter. Is it possible to make, say, 2 or 4 of the trees in PETG? Maybe that would be enough to keep it anchored.
i was thinking something along those lines too, but i'd have to build them into the model. petg is a bitch to clean off of the pei plate.