Closed geometry
The model must be a watertight solid, not an open collection of surfaces. Holes, duplicate faces and reversed faces cause preparation errors. Most CAD and modelling applications can inspect and repair a mesh. Use that function before exporting.
Units and size
STL does not store a unit. Export in millimetres and check the size in the preview after upload. A model that suddenly appears ten times too large or too small was usually exported in the wrong unit. You can correct it with scaling in the configurator.
Wall thickness
Very thin walls cannot be printed reliably. As a guide, structural walls should be at least 1.2 mm thick, while freestanding details should generally be thicker. Delicate points and extremely thin edges may break or fail to print.
Overhangs and supports
Steep overhangs require support structures in FDM printing. We remove them and include them in the print time. If you can orient or split the model to need fewer supports, the print will generally be cleaner and less expensive.
Details that may disappear
Raised or recessed text less than roughly 1 mm deep with strokes under 0.8 mm often becomes unclear in FDM printing. Make text and fine patterns more generous or choose a finer layer height.