2STEP-Converter - v2.0.0 - Last but not least
TL;DR - I built a free, open-source tool that batch-converts STL/3MF/OBJ/AMF/IGES files into editable STEP solids, because I was tired of doing it manually in FreeCAD every time I downloaded a model.
Hey everyone,
If you're into 3D modelling you've probably grabbed free STL models online and then wanted to tweak them - change a dimension, cut something out, adjust a feature. STL is a dead-end mesh format though, so to edit it properly in a solid modeller like Plasticity you need a STEP file first.
Every single time I found a model I liked and wanted to modify, I had to go through the same manual ritual in FreeCAD: open STL, "Create Shape from Mesh", "Refine Shape", export STP. Over and over. It's only a few clicks but it gets old fast, especially when you have a handful of files to process.
The thing that actually wore me down wasn't the clicking itself, it was the rhythm of it. FreeCAD has to load the file. Then "Create Shape from Mesh" takes a few seconds to think. Then "Refine Shape" thinks again. Then you save, close, open the next file. You can't really do anything else during it because each step needs you to confirm something, but you can't really focus either, because you're just waiting in 10-second bursts. After half an hour of that on a folder of free downloads, you start questioning your life choices.
I looked around for a proper solution but couldn't find anything that just worked - the only reliable option was FreeCAD, and even then it was a manual step-by-step process for every single file. There are a bunch of online converters but most of them just wrap the mesh as-is, so what you get is a STEP file made of thousands of flat triangular faces. Technically a STEP file, but completely useless for actually modifying anything.
So I automated it. This was a fun little project built purely to fill my own need, so there might be some rough edges or edge cases I haven't hit yet - but it works well for me and hopefully for you too.
What it does
You drop your STL / 3MF / OBJ / AMF / IGES files into a folder, run a launcher, and editable STEP files come out the other side. Each result also gets a small preview image so you can glance at a folder of outputs without opening a CAD app for every one.
The bulk of what I use it for is printable models - phone holders, brackets, replacement parts, enclosures, that kind of thing. Stuff that started life in someone's CAD tool and got exported as STL for sharing. Those convert almost perfectly because the source mesh is just a thin tessellated skin over real geometry, and the tool effectively rebuilds that geometry. You import the result into Plasticity (or whatever you use) and it's just there as a proper editable solid, with faces and edges you can select and modify.
Scanned models work too, but you'll get a more approximate solid. Usually good enough to use as a reference body to model on top of, not always good enough to use as the final part. That's not really a tool problem, that's just the nature of going from a noisy point cloud to clean CAD topology.
A few honest caveats
- If your source mesh has holes in it (common with scans or sloppy exports), the result won't be a perfectly closed solid. A quick pass through Blender or MeshLab to patch it tends to fix that.
- Color, materials, and textures aren't preserved. Just the geometry.
- Clean, dense exports come out beautifully editable. Sketchier meshes need a bit of experimentation with the reduction setting, but it's forgiving once you find a sweet spot.
- It doesn't replace your CAD tool. It just removes one annoying step at the front. You'll still do the actual editing wherever you normally would; this just gets you from "STL on Thingiverse/Printables/MakerWorld" to "thing I can work with" without the conversion ritual in between.
Practical stuff
Works on Windows, macOS, and Linux. Free, open source, and there's nothing to install beforehand - the launcher sorts itself out on first run. The first launch takes a little while because it downloads everything it needs, but after that it's instant.
All the actual CAD heavy lifting is done by the OpenCASCADE team - the same engine that powers FreeCAD. I didn't write any of the conversion math; I just made it easier to run on a folder of files and added a few quality-of-life things like previews and ETA estimates. Genuine thanks to that whole ecosystem - without them this would've been a years-long project instead of a weekend one.
Everything else (install steps, options, troubleshooting) is on the GitHub page:
github.com/yaneony/2STEP-Converter
One last thing
I'm treating this as the final stable release. I've been working on it solidly for about a week and it's at the point where it does everything I set out for. There won't be big new features from here on, just bugfixes if someone runs into something that breaks. I'd rather ship a small finished tool than a sprawling half-finished one, and this comfortably falls into the "small and finished" category. Last release, but not a least one - it's done because it works, not because I'm walking away from it.
That said, if you do try it, I'd genuinely love to hear how it went - especially if you find a mesh that breaks it, because that's exactly the kind of thing a bugfix patch could address. Even just a "this saved me an hour" comment goes a long way when you've spent a week on something for your own use and put it out there hoping it helps someone else too.
And if it ends up genuinely useful to you and you feel like throwing a coffee my way, I have a Ko-fi here: ko-fi.com/yaneony. Any support is hugely appreciated, but absolutely zero pressure - the tool is free and always will be, and a comment in this thread means just as much.
