Convert CATPart to STL
CATIA V5 writes STL from Save As, and the dialog asks you nothing. The quality of the mesh is decided somewhere else entirely — by a display setting in the options — which is why CATIA exports so often come out faceted, and why the fix takes ten seconds once you know where it is.
We cannot read .CATPart or .CATProduct files. The format belongs to Dassault Systèmes and is closed, so no browser tool opens one. The export has to happen in CATIA, or the sender has to give you a STEP file, which we can convert.
Saving a CATPart as STL in CATIA V5
Written for CATIA V5. The 3DEXPERIENCE platform, sometimes called V6, exports through its own Export command and keeps its files in a database rather than on disk.
Set the accuracy before you export
Tools → Options… → General → Display → Performance → 3D Accuracy
This is the setting that decides the mesh. CATIA writes the STL from the same tessellation it uses to draw the part on screen, so a display tuned for speed produces a coarse file.
Choose Fixed and set the value to 0.01. That is the finest the slider goes, and it means no triangle sits more than a hundredth of a millimetre off the true surface. Proportional scales the accuracy with the size of the part, which is why a large part exported on the default looks faceted.
Show only what you want in the file
Right-click a body → Hide/Show
The export takes what is visible. Construction surfaces, reference bodies and anything else left showing can end up in the STL beside the part, so hide them first.
Save As, and choose stl
File → Save As… → Save as type: stl
There is no options button and no further dialog. CATIA writes the file as soon as you press Save, using the accuracy you set in the first step.
Put the display accuracy back
Tools → Options… → General → Display → Performance → 3D Accuracy
A fixed accuracy of 0.01 makes large assemblies slow to rotate. If CATIA felt quicker before, return the setting to what it was once the file is written.
Check the result
(in the STL checker on this site)
Drop the STL in and compare the measured size with the part. CATIA works in millimetres unless somebody changed the document, so the numbers should match the model exactly.
Why a CATProduct cannot be saved as STL
Open an assembly, go to Save As, and stl is not in the list. That is not a licence problem. A .CATProduct holds positions and references to part files rather than geometry, and the STL export is only offered for a document that holds a shape.
The way through is to turn the assembly into a single part first. With the product open, use Tools, Generate CATPart from Product. CATIA builds a new CATPart containing one body per component, in their assembled positions. Save that as STL in the usual way.
The dialog offers to merge all the bodies of each part into one, which keeps the result tidy. What it does not do is fuse touching components into a single solid — the STL holds each one as a separate closed shell, overlapping wherever the parts overlapped. For printing an assembly as separate pieces, export each part on its own instead.
The other route: the STL Rapid Prototyping workbench
CATIA has a workbench made for this job, under Start, Machining, STL Rapid Prototyping. It needs its own licence, which many seats do not have, and where it is available it is the better tool.
Its Tessellation command asks for a sag value directly — the same deviation the display setting controls, but set for this one export instead of for the whole session — and lets you inspect and repair the mesh before writing it with the Export command.
If the workbench is greyed out on your seat, the display accuracy route above gives the same geometry. It is simply less convenient, because it changes how everything on screen is drawn while it is switched on.
If you do not have CATIA
This is the usual case. CATIA is expensive, there is no free edition, and nothing outside it reads a CATPart except commercial translators that cost real money themselves.
So ask for STEP. In CATIA it is File, Save As, with the type set to stp, and it works for assemblies as well as parts. Every company that uses CATIA sends STEP files to suppliers as a matter of routine, so it is a normal request and not an awkward one.
A STEP file from CATIA carries the exact surfaces, the assembly structure and the part names. It converts to STL on this site, in your browser, with a setting for how fine the mesh should be — which puts the decision CATIA hides in its display options in front of you. IGES, the older exchange format CATIA also writes, converts here too.
Where we can actually help
Ask for STEP and the rest runs here: STEP or IGES to STL at a mesh density you choose, with nothing uploaded — which matters for parts that are under a supplier agreement.
Questions
- Why is my STL from CATIA so faceted?
- The export uses the on-screen tessellation. Go to Tools, Options, General, Display, Performance, set 3D Accuracy to Fixed at 0.01, and save the STL again.
- How do I convert a CATProduct to STL?
- Not directly. Use Tools, Generate CATPart from Product to make a single part from the assembly, then save that part as STL. Or export each component part separately.
- Can I open a CATPart without CATIA?
- Not with free software. The format is closed and only commercial translators read it. Ask the sender for a STEP file, which CATIA writes from Save As and which opens everywhere.
- Is there an online CATPart to STL converter?
- Not one that runs in your browser, and we do not offer one. Converting STEP to STL does run in the browser, so the practical route is a STEP export from CATIA followed by a conversion here.
Where to go next
Related guides
Tools that do part of this here
About these formats
Checked against current software versions on 2026-10-09