What an assembly file actually contains
A SLDASM is a document about arrangement. It records which components belong to the assembly, where each one sits, how they are mated and constrained, and the structure of any sub-assemblies. What it holds about the components themselves is a reference: a pointer to the SLDPRT file where that shape lives.
So an assembly on its own is a set of instructions for putting together parts you do not have. Opening it produces an empty or broken assembly, and converting it produces nothing, because there is nothing there to convert. Both are correct behaviour for the file you were given.
The person who sent it almost certainly does not know. On their machine the parts sit in the same folder or in the same PDM vault, so the assembly opens perfectly and looks like a complete file. This is a genuinely easy mistake, and worth being gracious about.
How to tell before you waste time
- One small file arrived on its own
- An assembly of any real size that is only a few hundred kilobytes is almost certainly references and no geometry.
- You got a .sldasm and no .sldprt files
- Not decisive on its own. Some assemblies keep their components’ shapes inside the assembly file, and those convert here with every component in place; the rest have nothing to show without the parts. Uploading it is the quickest way to find out.
- The viewer shows a tree with names but nothing in the window
- The structure loaded and the components did not resolve. Classic missing-references symptom.
- A conversion returns an empty or near-empty file
- Same cause. The converter faithfully converted nothing.
The counter-case is worth knowing too: assemblies sometimes do arrive complete, as a zip or folder containing the assembly alongside every part it references, or as a pack-and-go bundle. Those convert as a whole, and the component names are worth preserving so the result still reads as a product rather than one fused shell.
What to ask for instead
Ranked by how much it helps and how little it asks of the sender.
- A STEP of the whole assembly. One file, all the geometry, opens everywhere, thirty seconds of their time. This is almost always the right request and it ends the conversation.
- A pack-and-go zip, if you specifically need the native files. SOLIDWORKS has a built-in command for exactly this, which gathers the assembly and every referenced part into one folder.
- The parts folder as it stands, if they are willing to send the lot. Keep the folder structure — the references are paths.
- A STEP per part, if you need them separately. More work for them, so only ask if you actually need it.
Wording that avoids a second round trip: "The assembly references its part files, so it arrived without any geometry. Could you send a STEP export of the whole assembly instead? File, Save As, choose STEP." That gives them the reason and the click path, and it is hard to get wrong.
If the parts did arrive
Keep the assembly and its parts in one folder, then convert the assembly. Components keep their names, so the output remains legible as a product.
On our servers. No account: deleted within 24 hours. Signed in: kept until you delete them. Never shared or used for training.
Two practical limits. Assemblies over five components need a free account, because an assembly is one upload but many parts of geometry to process. And the size cap depends on what you convert TO: a free account converts up to 300 MB to a mesh format like STL, or 140 MB to STEP, Parasolid or SLDPRT, which cost about twice the memory to rebuild as a solid. Maker and Studio raise those to 830 MB and 380 MB, and will keep a file up to 1536 MB even when it is too big to convert.