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?
265C is cooking the PETG. I never go above 230C.
the datasheet for this one recommends 255, which is also within range of the preset in orcaslicer. common wisdom on the web seems to be to go above the specified temps for petg, rather than below, with some people recommending 280 degrees.
265°C is reasonable for a fast CoreXY printer.
230 is on the low range for PETG, the reason many manufacturers recommend it is because of people with PTFE-lined hotends who don't want cancer. 250 is what I tend to do. As always, do what works for you!