Convert SLDPRT to STP

Why STEP rather than STL

An STL is triangles. It is the right answer when the next thing that happens is printing, and the wrong answer for almost everything else, because the moment a curve becomes triangles the fact that it was ever a curve is gone.

STEP stores the actual geometry: a cylinder as a radius and an axis, a fillet as a real blend surface, a spline as a spline. The recipient can measure it exactly, machine from it, cut a section through it, or use its faces as references for their own design. None of that works reliably from a mesh.

It also carries an assembly tree with named components, the units, and a tolerance describing how accurately the surfaces meet. An STL carries none of those.

The one thing STEP does not carry is the feature history. The recipient gets the finished shape as exact surfaces, not your extrudes and cuts — so they cannot change a dimension and have it rebuild. That is deliberate: the feature history is specific to SolidWorks, and STEP is a format for exchanging shapes between programs that model in different ways.

AP203, AP214 and AP242

These are application protocols — subsets of the STEP standard aimed at different jobs. All three describe the same kind of geometry and any program that reads one reads the others.

AP203 is the oldest and the most conservative. Geometry and assembly structure, no colour. Choose it only if the recipient specifically asks, or if something in their pipeline is old enough to be fussy.

AP214 adds colour and a few other presentation features, and it is what most CAD programs default to. It is the safe choice for almost every situation.

AP242 is the current standard and merges AP203 and AP214, adding product manufacturing information — tolerances and annotations carried as data rather than as drawings. It is the right answer where both ends support it, and support is good but not universal.

If you do not know what the recipient uses, send AP214. If they come back and say their software will not open it, AP203 is the fallback.

What you can do with the STEP file here

Once SolidWorks has written the STEP file, the rest runs on this site, in your browser, with nothing uploaded. Reading STEP needs a CAD kernel, because the file describes surfaces mathematically rather than as triangles, and the one built into these pages is the same open kernel FreeCAD uses.

STEP to STL is a real conversion with a mesh density setting, the same decision SolidWorks asks you to make in its own STL export. STEP to OBJ, GLB, 3MF and PLY work the same way, and an assembly keeps its parts separate where the target format can hold them.

The other direction exists too, with a caveat worth stating plainly. A mesh written as STEP is a faceted solid: every flat region becomes a face, and a cylinder is still a ring of flat strips. It opens in SolidWorks and is useful to measure and reference against, and it is not the part you started with.