How to Prepare an STL File for 3D Printing

1. Make Sure It's Watertight

A printable model needs to be a single, solid, "watertight" (manifold) shape with no holes in the mesh, no flipped faces and no stray internal geometry. Slicers struggle with open edges and overlapping shells, which can show up as missing walls or odd artefacts in the print.

Most modelling tools have a "check" or "repair mesh" option, and free tools can auto-heal common issues. If you're not sure, send it anyway, we check every file before printing and will flag anything that needs fixing.

2. Get the Scale and Units Right

STL files don't store units, so a model can arrive ten times too big or too small depending on how it was exported. Tell us the intended real-world size (in millimetres) of at least one dimension, for example "about 80 mm tall". That one number lets us scale it exactly the way you pictured it.

3. Mind the Wall Thickness

Very thin walls and fine details can come out fragile or fail to print at all. As a rough guide, keep walls and raised details at least 1 mm thick where you can, and a little more for anything that needs to take handling. Tiny text and razor-thin fins are the usual culprits, so flag them if they matter and we'll advise what will hold up.

4. Design for Fitted Parts

If your model has parts that slot together, or a hole for a screw, peg or magnet, build in a little clearance rather than making them the exact same size. FDM prints have small tolerances, so push-fits often come out tight. A margin of around 0.2 mm to 0.5 mm is a good starting point. There's more on this in our FAQ, and if fit is critical we can print a quick test piece first.

5. Think About Orientation and Supports

You don't need to add supports yourself, we set those up as part of preparing the print. It does help to know which face is the "show" side, though, because the bottom and any supported overhangs can be slightly rougher. If a particular surface needs to look its best, just mention it.

6. Choose a Material (or Ask Us)

Whether a piece should be PLA, PETG or something tougher depends on how it'll be used. If you're not sure, our PLA vs PETG guide is a good primer, or tell us what the part is for and we'll recommend one.

7. How to Send Your File

• Format: STL is ideal. STEP, OBJ or 3MF are fine too.
• Sharing: upload to Google Drive, OneDrive or Dropbox and paste the link, our contact form has a field for it.
• Include: the size you want, colours, quantity, any deadline and what the piece is for.

No file yet, just an idea? That's fine too, see how custom printing works or browse the gallery for inspiration.