Best way to convert a .stl fileinto a .step file?

I’ve found various models that I want to remix. The few that come with .step files I can easily work with in fusion360. Not so for the .stl files. Unfortunately, fusion360 wants me to pay for a license for it to allow me to use the .stl to .step file conversion that’s built into it. So, is there some other way to do it?

Or is this the point where I give up on fusion360 and move to onshape or some other cad?

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When I import a stl mesh into F360.

I bring in the mesh, then place at 0,0.

I convert the mesh to a body.

Then I export it as a .step file to my preferred location on my server.

I hope this is what your looking for information wise.


Are you using the prismatic conversion? I find that’s where it wants the $$$.

Well, OK, apparently it is just barely possible to accomplish it using faceted conversion instead (still free), but it’s a lot more work:

That said, even this hamstrung method looks to still be better than what onshape currently has. :roll_eyes: Maybe some other form of free cad has something like the prismatic conversion? If so, that in itself would be a good reason to switch.

There are some stl to stp online conversion for free. I never used them because my 3D software has no issue with stls but you may want to give them a try. Just google for online stl to stp.

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Aha. Which one do you use?

Yes It’s a work around that has many steps but it is the free way. :blush:

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OK, I just tried the first 6 of them on the list that google found, and–no surprise–all but one (?) of them failed. The one that said it did the conversion would only provide the file if I downloaded their executable to get it. No mention of that requirement beforehand. Uh, sure… And then what demands come after that? Sounds like a honey trap to me, with ransomware as the payload. Anyhow, I’m not willing to risk it. Frankly, even if it were legit, you’d have to be stupid to accept an offer like that from a random, unknown website. And the people running it should know that.

I’m guessing that if it truly could be done automatically, then at least one of the CAD packages would have a tool to do it. QED that most likely all the “free conversion websites” are fake. On the other hand, if someone can recommend one in particular that really does work, I’d be happy to try it.

The one whose legitimacy I question is:

I probably convert 1-2 online STL models to STEP each week. I do this mainly because I need to modify something in CAD and STL files are a lot more difficult to work with.

I’ve been searching for the holy grail of conversion utilities, some very expensive. NEWS FLASH: THEY ALL SUCK!!!

Among the one’s that I found to be the least suckiest :yum: is this one. It has been my go-to for a long time now and I still go back to the other online services to see if they have improved and they have not.

A tip

None of the online tools work well if you exceed the maximum number of vertices. Unfortunately, that is not a hard rule as the complexity of the object(the number of surfaces and angle) will greatly reduce the max vertices that the tool can translate.

So here a tip. Bring the model into either Bambu Studio or Microsoft’s 3D builder. Both have the ability to simplify any model. Then re-export the simplified 3D model and upload that into the online converter. This does not come without a cost. A simplified model achieves it’s simplification by removing surfaces. Have you ever wondered how they do those simple Low-Poly models? Well… that how. The fewer the number of vertices, the less work the translator has to perform but at the expense of a “faceted” looking model.

Here’s an example of a high resolution sphere. Note that this level of resolution cannot be achieved in Bambu Studio but rather in CAD and then exported. I’m deliberately using a very small 10mm sphere.

Now let’s take the high res sphere and use the simplify tool to reduce the number of polygons in order to show an extreme example. In this case, it went from 5040 triangles to 196. Don’t be fooled by the squares, those are actually two triangles.

Ugly? Right?



FreeCad also permits the conversion of .stl to .step using a simple procedure.
However, it is prone to fail and F360 to freeze for complex geometries. In that case, I only succeeded by manually simplifying the mesh, if necessary, further simplifying using, e.g. F360, and afterwards trying to convert. The success rate is low, and it demands a significant effort.
Another option is meshmixer, but with additional complexity (at least for me).

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Just my five cents:

STL is great if YOU design things and if you do it right.
They not for smooth, organic shapes or such…
Converting a STL to STEP in order to work with it is (for me) like cutting 3mm plywood with a a chainsaw to create xmas ornaments…
The result just sucks…

When I started with 3D printing there was only STL files to use, OBJ came later but still wasn’t good for 3D printing.
No one cared though as the actual hardware and firmware was on par with the low quality.
Today though any printer and slicer is able to use arcs properly, to reduce the resolution of a model where the details get too fine and so on…
If you want something round in your model than you need a format that supports it - STL only supports straight lines when it comes to printing.

The change came with the machines and even more so thanks to more slicers supporting more formats.
The thing we still don’t have is a universal 3D software created for the purpose of 3D printing and not design or modelling.
Fusion360 is very hard to keep active as the free version and for most users just overwhelming.
But it supports all vital file formats and design options anyone could ever ask for.
At a hefty price if you need it for more than pure private use.
Below that and despite all those years there isn’t really much…

We have things like Sktechup, Blender, Tinkercad, Scad and what not…
All good for something, all with a certain learning curve and they all suck if you want it all.
Take something as basic as creating a threaded bolt - to DIN specs or such, not a fanatasy one…
A nightmare in things like Sketchup, next to impossible using Blender and the rest, while able to with a few clicks fails to consider that a printed thread and nut never fit together - unless you tweak things…

What I really would love to see and even be willing to pay for is this:
A modular 3D sketching and design software capable or organic/sandbox modelling when required.
Different tool bars, customisable to a user’s needs…
Like for the beginner just some basic solids with the usual trimming, cutting and merging options.
For the more advanced users a parametric approach or a fully fetched toolbar setup.
Most important thing however would be the inclusion of 3D printing on a design level.
For example:
A pin and hole of 10mm diameter would never fit is designed like this.
For a decent laser cutting ‘slicer’ I can set a kerf - which provides an offset to ensure that what the laser left WILL fit.
If we know our printer needs a hole to be 0.12mm larger than the pin we could just click on holes or pins and other things that need to fit together to apply this 0.12mm extra or less…
Yes, we can do this ‘offset’ in any half decent slicer these days - but did you actually ever check it for different diameters or square fits :wink:
It is like a fuzzy factor added that only too often won’t produce the same ‘gap’ with largely different object sizes.
I do wonder for a few years though if this lack of dedicated software IS intentional…



It’s not entirely true though, it happens sometimes that the stl is so buggy that solidworks only accepts import as feature rather than solid body and the model is then almost impossible to modify or takes too long to repair. In this case unless I need to modify it a lot, I find it easier to just use modifiers, add parts or negatives or cut parts and combine in bambu studio, perform a boolean mesh and save the modified stl for later use (when boolean mesh does not work, I export the project).


I love that analogy, it is so spot-on. :+1: