Most failed props are not a bad STL. They are a first-layer problem. Do these five before you throw more filament at it.

1. Wash the bed. IPA is not enough.

Dish soap and water. Finger oil on PEI is the usual reason the first layer lets go at hour two.

2. Dry filament before you touch temperature.

PETG and even "sealed" PLA pick up moisture. If the first layer looks fuzzy or will not stick, dry 4–6 hours. New temperature profiles will not fix wet filament.

3. Print a 25 mm square, not the whole model.

0.2 mm, one square. If that fails, the prop will fail. Fix adhesion on the square first.

4. Elephant foot is not under-extrusion.

Fat first layer, clean walls after that: drop bed temp 5°C, or a tiny negative initial-layer expansion. Do not crank flow.

5. Know when it is the printer, not the file.

If every STL fails the same way — clogs, skipped layers, homing errors — that is hardware. A clean STL will not clear a nozzle.

Print-ready prop files and a live hour on the printer are two different products. Buy the one you actually need.

Questions on a specific fail: comment with printer, filament, and a photo of the first layer.