How to prepare an STL for 3D printing

1. Check the size before ordering

STL files don't store units. A model designed at 50 mm but exported in inches or centimetres can arrive 25 times too big or 10 times too small. Export in millimetres, check the overall dimensions in your CAD tool, and compare them with the size the quote shows after upload.

2. Watertight (manifold) geometry

The mesh should be a closed surface with no holes, gaps, flipped faces or stray edges — “watertight” or “manifold”. Non-manifold geometry can make a slicer produce missing walls, gaps or stray infill. The quote tool flags meshes that aren't watertight, and minor holes can usually be repaired automatically at no charge. For bigger problems, most CAD and mesh tools have a “repair” or “make solid” function.

3. No unintended duplicate bodies

Check the export doesn't include hidden construction bodies, overlapping copies of the same part, or reference geometry. They print as real plastic. If you want several copies, export one and set the quantity on the quote instead.

4. Wall thickness and small features

Very thin walls may not print reliably. As a rule of thumb, keep walls at least around 1 mm (thicker for parts that need to be sturdy). Text, fine ribs and small pins narrower than about 0.5 mm are the usual casualties on a standard nozzle — see why details disappear when sliced.

5. Holes, fits and clearances

FDM parts have real-world tolerances: holes usually print a little small, and two parts modelled at exactly the same size won't fit together. Add clearance (as an illustrative starting point, a few tenths of a millimetre on a hole's diameter) rather than modelling an exact fit, and test critical fits with a single print first. Typical values are in why 3D printed holes come out too small.

6. Orientation and supports

You don't need to set up orientation or supports. Layer & Loop Store orients and supports each part when preparing the order, balancing strength, finish and reliability. Send the model the right way up in your own CAD sense, and if one face must look best or the part takes load in a particular direction, say so in the order notes. More in orientation and supports.

7. Colours, material and quantity

• Colours: single-colour prints just need a colour picked on the quote; multicolour prints need a painted 3MF (see STL vs 3MF).
• Material: PLA+ suits most indoor parts; heat, outdoor use or flexing may need another (material guide).
• Quantity: order spares together — each additional identical copy costs less.

Quick pre-upload checklist

• Exported in millimetres, and the measured size looks right.
• Fits within 250 × 250 × 250 mm, or split into pieces.
• Watertight, with no stray or duplicate bodies.
• Walls around 1 mm or thicker; small text and details big enough.
• Clearance on holes and mating faces.
• Notes ready for visible faces, load direction or intended use.
• Material, colour and quantity decided.