PETG Corners Lifting After 6–7 Hours Despite Good First Layer
Printer is an Ender 3 V2 with a PEI spring steel sheet. I'm slicing in Simplify3D v5.1.2. Material is Overture PETG (1.75 mm), nozzle 240°C, bed 80°C. Layer height is 0.2 mm with a 0.4 mm nozzle, print speed around 45 mm/s and cooling fan at 20% after layer 5. The part is a mounting bracket that's roughly 230 × 140 mm and takes about 9 hours to print. The first layer always looks excellent with good adhesion across the entire bed. For the first 5–6 hours everything stays flat, but around hour 7 one rear corner starts lifting a couple of millimeters. Once that happens the nozzle lightly hits the raised corner on every pass, leaving small scars on the top layers. The print usually finishes, but the bottom is no longer flat enough for the part to bolt onto an aluminum plate. I've already tried increasing the brim from 5 mm to 12 mm, cleaning the PEI with IPA before every print, lowering the cooling fan from 40% to 20%, and printing inside a simple enclosure to keep drafts away. None of those changes completely solved the problem. Are there any process settings you've found that help reduce internal stress on larger PETG parts? For example, changing outline order, infill overlap, infill pattern, or reducing print speed after a certain height? I'm trying to avoid redesigning the part if there's something in the slicer I'm overlooking.
