Convert SLDASM to STL
An assembly export has one decision a part export does not: whether you want the whole assembly as a single STL, or every component as its own file. For printing, that decision is usually the difference between a useful export and a useless one.
We cannot read .sldasm files. Beyond the format being closed, an assembly file holds only references to its part files — the geometry lives in the .sldprt files it points at. A .sldasm on its own is not enough even for SolidWorks, which is why sending one without its parts never works.
Exporting an assembly from SolidWorks
Open the assembly with all its components resolved
Right-click the top of the tree → Set Lightweight to Resolved
A lightweight component is loaded as a preview rather than as full geometry, and lightweight parts can export incorrectly or not at all. Resolving everything first takes a moment and avoids a silent gap in the output.
Start the export
File → Save As… → Save as type: STL (*.stl) → Options…
Same route as a part. The options dialog gains an extra section for assemblies, which is the part that matters here.
Choose one file or many
Output as → Do not translate STL output data to positive space · Save all components of an assembly in a single file
Ticked gives you one STL containing everything, in assembled positions. Unticked gives you one STL per component, each in its own coordinate system.
For printing, you almost always want them separate. A single STL of an assembly is one merged lump of triangles where the parts interpenetrate at every mate — you cannot print that, and you cannot pull it apart afterwards.
Keep the assembly coordinate system
Do not translate STL output data to positive space (tick it)
With this ticked, every exported part keeps its position in the assembly rather than being moved to sit in positive coordinates. That is what lets you reassemble them correctly at the other end if you need to.
Set the resolution and units as for a part
Resolution: Custom → Deviation 0.01 mm · Angle 5° · Unit: Millimeters
The same numbers work. Remember that these apply to every component, so a small fastener and a large housing both get the same tolerance — which is another reason separate files are easier to manage.
Save, then check each part
OK → Save
Drop the results into a converter here to confirm the sizes. It is worth checking a small component in particular, since a tolerance that suits a large housing can leave a small threaded feature visibly faceted.
Why an assembly as a single STL is usually wrong
In CAD, an assembly is a set of parts held in position by mates. The parts touch, and frequently they overlap by design — a bolt in a hole, a press fit, a component that sits in a recess. None of that is a problem because each part is a separate solid.
Merge them into one STL and all of that becomes one body of triangles with surfaces passing through each other. A slicer handed that has to guess what is inside and what is outside at every intersection, and the guesses are not always consistent. The result is usually printable-looking and wrong.
It is also, obviously, printed as one piece. An assembly that was meant to come apart does not.
So export separately, print each part, and assemble them afterwards. The one case for a single STL is when you genuinely want the assembled shape as one object — a display model, a shape study, something to show a client.
Why a .sldasm alone is never enough
A SolidWorks assembly file stores references to part files, plus the mates that position them. It does not store the geometry. Open an assembly whose parts are missing and SolidWorks tells you it cannot find them — the file genuinely does not contain the shapes.
This is why emailing somebody a .sldasm achieves nothing, and it is also why no converter could ever help even if the format were open. There would be nothing inside to convert.
If you are sending an assembly to someone, use Pack and Go — File, Pack and Go — which gathers the assembly and every part it references into one folder or zip. Or, far simpler, export a STEP file: STEP stores an assembly tree with the real geometry of every part inside it, in one file that anyone can open.
If you do not have SolidWorks
Ask for a STEP file. For an assembly this is even more clearly the right request than for a part, because STEP carries the whole assembly — every component, its geometry and its position — in a single file that FreeCAD, Fusion 360, Onshape and every free viewer will open.
The alternative, asking for STLs, means asking for a folder of files and then working out how they fit together. STEP keeps that information.
Pack and Go is what you want if the other person insists on sending native files and you do have SolidWorks. It is not a conversion, just a gathering, but it is the difference between a file that opens and one that does not.
Where we can actually help
Once you have STLs of the individual parts, converting them to 3MF here records the units in each file — useful when you are handing a set of parts to somebody else to print.
Questions
- Should I export one STL or one per part?
- One per part, for anything you intend to print. A single merged STL has every mated surface passing through another, which a slicer cannot interpret reliably, and it cannot be taken apart afterwards.
- Someone sent me a .sldasm and it will not open.
- An assembly file holds only references to its part files, not the geometry. Without the parts there is nothing to open. Ask them for a STEP file, or for a Pack and Go archive if you have SolidWorks.
- How do I keep the parts in their assembled positions?
- Tick "Do not translate STL output data to positive space" in the STL options. Each exported part then keeps its assembly coordinates instead of being moved to the origin.
- What are lightweight components and why do they matter?
- SolidWorks loads large assemblies with some components as previews rather than full geometry, to save memory. Lightweight parts can export incorrectly. Right-click the top of the tree and choose Set Lightweight to Resolved before exporting.
Where to go next
Related guides
Tools that do part of this here
About these formats
Checked against current software versions on 2026-09-11