topic Re: Joining two existing STL files in Fusion Design, Validate & Document Forum

Joining two existing STL files

dhuninkUA72Q — Wed, 15 Jan 2025 20:58:06 GMT

Hi,

I'm trying two existing STL files. They are intended to be printed separately and then connected together, but I wan to print them as one.

So far I've imported both into Fusion as meshes and generated face groups. But after a lot of searching I stil havent found the correct way to align the two pieces so that they connect. How can I achieve that?

I think the image below speaks for itself.

Re: Joining two existing STL files

etfrench — Wed, 15 Jan 2025 21:34:10 GMT

There are several different ways to do that.

Measure the distance between the two and use the Move command.
Create a Mesh section sketch of the two bodies. Edit the sketch and use the Fit Curves to Mesh Section tool to create an accurate profile of each. Measure and Move.
Put each body in a separate component. Use the sketch in option 2 to create sketches on each body. Create joint origins on each. Use a rigid joint to position them.
Convert the meshes to solid bodies. Use a joint to position them.

Re: Joining two existing STL files

TheCADWhisperer — Wed, 15 Jan 2025 21:40:31 GMT

@dhuninkUA72Q

Can you File>Export your *.f3d file to your local drive and then Attach it here to a Reply?

Someone will create a video of the process.

Re: Joining two existing STL files

dhuninkUA72Q — Thu, 16 Jan 2025 20:46:00 GMT

Hi would highly appreciate that!
I've attached the .f3d file here.

Re: Joining two existing STL files

dhuninkUA72Q — Thu, 16 Jan 2025 20:55:53 GMT

Thanks for the suggestions. With option 4, I did got what I wanted. However, when one challenge is defeated, another opens 😉
I've been able to delete the faces for the left component so it becomes a single face, but when I try to do that on the richt component, Fusion says "compute failed".

Re: Joining two existing STL files

etfrench — Thu, 16 Jan 2025 22:06:26 GMT

If you are just going to 3d print this, then the facets don't matter. You can use a joint to position them even with the facets after converting them to solid:

Converting them to solid using Parametric/Prismatic also works but sometimes it doesn't remove all of the facets and sometimes it does.

Re: Joining two existing STL files

dhuninkUA72Q — Fri, 17 Jan 2025 09:31:23 GMT

Ive tried converting the parts using parametric, but if I then add a joint, the parts get oriented wrong.

What am I doing wrong here? See the attached files.

Re: Joining two existing STL files

TrippyLighting — Fri, 17 Jan 2025 11:47:41 GMT

@etfrench wrote:

Converting them to solid using Parametric/Prismatic also works but sometimes it doesn't remove all of the facets and sometimes it does.

The faces don't combine because they are not coplanar. This means the very simple geometry of this imported mesh is garbage!

Re: Joining two existing STL files

etfrench — Fri, 17 Jan 2025 18:39:30 GMT

Select the midpoints of the faces instead of the edges. This image shows the currently selected joint origin which will only allow the pieces to be rotated around that edge:

Selecting the midpoint origin allows the components to be flipped and rotated to the correct position.

Re: Joining two existing STL files

etfrench — Fri, 17 Jan 2025 18:48:25 GMT

The results aren't consistent, which one would expect given the same inputs. I think garbage may be a little strong but accurate😁 Fortunately, it probably won't show when 3d printed:

Re: Joining two existing STL files

dhuninkUA72Q — Fri, 17 Jan 2025 19:52:36 GMT

And by garbage, you mean the stl files that I have been imported?
I won't put it that way, but I do know they have been created with Blender, which to my knowledge is no CAD-software and therefore produces export files which lags correct geometry. But I might be wrong there, and if so, I'm happy to be corrected 😉

Re: Joining two existing STL files

dhuninkUA72Q — Fri, 17 Jan 2025 20:26:03 GMT

That does seem to do the trick, thanks!
I need to add a lot more existing STL files to it and I'm not yet sure if I can use this same method over and over again. Is this the the most advised method when joining two stl files?

Re: Joining two existing STL files

TrippyLighting — Fri, 17 Jan 2025 20:37:39 GMT

They are garbage from the viewpoint of CAD modeling software.

Under the hood, CAD software represents geometry in the form of analytic geometry and NURBS surfaces. In most parametric solid modeling software those are stitched into BRep. Those are mathematical representations of geometry with topology and without limited resolution.

Triangulated meshes, on the other hand, have a finite resolution. When exporting CAD geometry into a triangulated mesh, the mathematical description and precision are lost. While such meshes visually still show remnants of topology they are difficult and often impossible to turn back into real CAD geometry.

Scanned meshes lack any topology information!

The goal of most of Fusion's mesh tools is to convert a mesh into solid or NURBS surface geometry.

The prismatic conversion does a fine job in this case because this is a very simple prismatic geometry.

The faceted conversion, as the name suggests, turns every triangle into a flat face. When in the solid tab, You can try to delete individual faces. Fusion will then attempt to auto-repair and merge adjacent faces that are coplanar into one cohesive face.

It works fine with one of these mesh objects; it doesn't with the other because the mesh lacks the necessary precision.

The reason for this is NOT that it was modeled in Blender. This shape can be modeled precisely in Blender. I doubt the person modeling this in Blender wanted to convert it into a solid model in Fusion, just to turn around and convert it back into a triangulated model for 3D printing.

Making one cohesive mesh from the two objects is also very simple to do in Blender 😉

Re: Joining two existing STL files

TrippyLighting — Fri, 17 Jan 2025 20:48:43 GMT

Can you share those .stl files?

Do you have access to the original Blender file?

You might have to zip those before attaching them to a post.

Re: Joining two existing STL files

dhuninkUA72Q — Sun, 19 Jan 2025 11:19:19 GMT

I don't have the original Blender files, but here are the STl files!

Re: Joining two existing STL files

dhuninkUA72Q — Thu, 23 Jan 2025 21:19:22 GMT

Thank you very much for elaborating in such detail. That actually helped me a lot in understanding why some .stl files would and others won't be easily editable when imported in Fusion.
The files shared here, are part of a larger project. All files have been created in Blender, and the author does not have all the original blender files anymore.
For 'simple' objects like this, I might be better off just recreating them in Fusion, if I understand correctly.
But how about more complex shapes, with curves? Does Blender recognize the correct topology from stl files that originate from Blender? If so, I should start learning how to import stuff in Blender and then export it with the correct topology so I can load them into Fusion. Or am I missing something here?

Re: Joining two existing STL files

TrippyLighting — Sat, 25 Jan 2025 14:16:03 GMT

Blender is vast, and that can make it confusing and challenging to learn. However, if the input to a design process is a triangulated mesh and the output is for 3D printing, which also usually generates triangulated meshes, then I would do this in Blender, as I show in the screencast.

(view in My Videos)