The upload page checks your file the moment it lands — size, wall thickness, overhangs, whether the mesh is closed. Here is what it is looking for, and how to get a clean pass on the first go.
1. Close the mesh
A printable model is watertight: every edge belongs to exactly two faces. Holes and stray faces confuse the slicer, which then guesses — and guesses badly. Most CAD tools have a mesh-repair or “make solid” step. Run it before exporting.
2. Give the walls something to be
Anything thinner than about 1.2 mm is thinner than two passes of our nozzle, and prints as a fragile single line or not at all. Text, fins, spokes and lettering are the usual casualties.
3. Look at your overhangs
A surface leaning more than roughly 45° from vertical needs support underneath it while it prints. We add that automatically and it costs a little material and time — but a model designed to avoid the worst of it comes out cleaner and cheaper.
4. Check the units
STL files carry no units. A model exported in inches arrives looking 25 times too small. The preview shows real millimetres the moment you upload, so glance at the dimensions before you go further.
STL, 3MF and OBJ all work. 3MF is the one we prefer — it carries units and colour, so there is less to guess.