Technical guide · 7 min read

How to prepare your 3D file for printing

A good 3D file is where every successful print starts: this guide shows you, step by step, how to check, repair and export your STL, OBJ, STEP or 3MF model. And if you have no file at all, we'll make one for you.

Accepted 3D file formats

STL: the universal standard (recommended)

The most widely used format in 3D printing. The model is described as a mesh of triangles. Simple, and compatible with every slicer and print service.

OBJ: with textures and colours

Similar to STL but supports UV textures and per-vertex colours. Useful for artistic models or colour renders, rarely needed for single-colour FDM printing.

STEP: maximum CAD precision

A CAD exchange format that keeps the exact geometry (NURBS curves, no triangulation). Ideal for precision mechanical parts, and the one we recommend for technical parts.

3MF: modern and compact

Developed by Microsoft and the 3MF Consortium. Holds geometry, colours, materials and metadata in one compressed file, and more and more modern software uses it.

Have another format (IGES, Fusion 360, SolidWorks)? Contact us: we can convert most formats.

Check your STL file before sending it

Run through this checklist first: a clean file means a faster, cheaper and better print.

1
A watertight (closed) model
Your model must be a closed volume, with no holes or missing faces (manifold). Imagine filling it with water: if the water could leak out, the model isn't watertight and the slicer can't tell inside from outside.
2
No inverted faces (normals)
Every face of the model has an inside and an outside, and all of them must point outwards. If some are flipped, the slicer can produce inconsistent results. Most software shows inverted faces in red or as transparent.
3
The right scale, in millimetres
3D printing works in millimetres: a 100 mm part must not measure 100 metres in the file. A common mistake is exporting in inches instead of millimetres, which makes the part 25.4 times too small or too large.
4
Walls at least 1.2 mm thick
Walls that are too thin can't be printed properly. With a standard 0.4 mm nozzle, the minimum is about 0.8 mm (2 perimeters), but we recommend 1.2 mm (3 perimeters) for good strength.
5
No details smaller than 0.4 mm
Details finer than the nozzle diameter (0.4 mm) won't be reproduced. Engraved text, logos and fine patterns should be at least 0.5 mm wide and 0.3 mm deep.
6
No hidden internal geometry, a sensible mesh
Remove faces hidden inside the model. Aim for a mesh resolution that is neither too low (visible facets) nor too high (a very heavy file): 50,000 to 500,000 triangles is a good target.

Free software to model and repair a 3D file

No 3D modelling software? These four free tools cover every need, from beginner to professional.

Blender: organic and artistic

Powerful open-source software for organic modelling, digital sculpting and animation. Ideal for figurines, characters and artistic shapes. It takes longer to learn, but there's very little it can't do.

FreeCAD: mechanical and technical

Open-source parametric CAD software for mechanical and technical parts. Ideal for replacement parts, enclosures and assemblies with precise dimensions. Exports STEP and STL.

TinkerCAD: beginners, quick jobs

A free web app from Autodesk, perfect to get started, with an intuitive drag-and-drop interface built on basic shapes. Great for simple geometric parts, limited for complex models.

Meshmixer: repair and supports

A free Autodesk tool for repairing meshes, analysing STL files and generating supports. Very useful for checking and fixing a file before printing.

Other free options for checking a file: 3D Builder (built into Windows) for a quick check and one-click repair, the 3D Print Toolbox add-on in Blender to analyse whether a model is manifold, and slicers such as PrusaSlicer or Cura, which flag mesh problems themselves.

Common STL file errors and how to fix them

Problem	Solution
My file is far too small or too large	Almost always a units problem. If your 5 cm part shows up as 5 mm, your software probably exported in centimetres instead of millimetres. Check the document units (mm) in your CAD software before exporting. In Meshmixer, resize with Edit > Transform.
The faces of my model are inverted (normals)	Some faces look transparent or a different colour in the viewer. In Blender, select everything (A), then Mesh > Normals > Recalculate Outside. Meshmixer's Inspector detects and fixes this automatically.
My model has holes in the mesh	Missing faces leave openings, so the slicer can no longer tell inside from outside. In Meshmixer, Analysis > Inspector finds the holes (blue markers) and fills them automatically. In Blender, select the edges of the hole and use Face > Fill (F).
Faces overlap or intersect	When two parts of the model pass through each other without being merged, the slicer can produce artefacts. In Blender, use the Boolean modifier (Union) to merge the volumes. In Meshmixer, Edit > Make Solid rebuilds a clean mesh from the visible volume.
The STL file is too heavy (over 100 MB)	Too much detail slows slicing without improving the print. When exporting, raise the angular tolerance (for example 15° instead of 5°). In Meshmixer, Edit > Reduce lowers the triangle count while keeping the shape.
Overhangs without support	Beyond 45°, supports are needed. Design your part to keep overhangs to a minimum.
Corrupt file	Export it again from your CAD software as a binary STL.

No 3D file? We'll model it for you

Don't want to learn modelling software? Send us what you have and our CAD modelling service creates the 3D file.

Detailed photos

Several angles, with a ruler for scale. The more photos, the better.

Dimensioned sketches

A freehand drawing with the key dimensions is enough for simple geometric parts.

The existing part

Send us the part, even broken, and we take precise measurements to model it.

Modelling is charged on top of printing. The price depends on how complex the part is: a simple geometric part costs less than a detailed figurine or an articulated mechanism. Contact us with your project for a quote covering modelling and printing.

You can write to us in English through the contact form (photos and files welcome as attachments), on WhatsApp or by phone at +33 7 59 72 51 81, or by email at contact@toulouse3dprint.fr. Is your file ready? Upload it on our order page for an instant quote: we check the quality of your file for free before printing.

Frequently asked questions

Which file format is best for 3D printing?

STL is still the most universal and widely supported format. For precision mechanical parts, STEP is better because it keeps the exact curves (no triangulation). 3MF is the most modern format, with colours, materials and metadata in a compact file. In practice, we accept all these formats at no extra cost.

How do I check that my file is printable?

Import it into Meshmixer (free) and run the Inspector tool (Analysis > Inspector). It automatically detects holes, inverted faces and intersections, marks them with coloured dots and can often repair them in one click. If in doubt, send us your file and we'll check it for free.

What resolution should my STL file be?

A file between 5 and 50 MB is a good balance. Too light (under 1 MB for a medium-sized part) and curved surfaces look faceted; too heavy (over 100 MB) and the file is hard to handle with no visible gain. In most software, an export tolerance of 0.01 to 0.05 mm gives an excellent result.

Do you accept Fusion 360 or SolidWorks files?

Yes. We accept native Fusion 360 (.f3d) and SolidWorks (.sldprt, .sldasm) files and most professional CAD formats; send them by email or through the contact form and we convert them in-house to the best format for printing. Sending the native file lets us control the quality of the export better.

Do you check my file before printing?

Yes, for free. If the file has a problem (holes, inverted faces, wrong scale), we let you know before printing.

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