Remesh Tool: How to remesh / convert a CAD file into a better STL
Difficulty: Intermediate
Overview: If are trying to edit a model made in a CAD program (CAD in the sense of being an engineering 3D modeling software) in another program such as Blender and have found that the model has horrible topology, this post is for you.
What is an .stl?
3D printing can take a file in a few formats, the most common format being an .stl. This is the typical format that all programs will export a file as in order to be 3D printed. Imagine it like a .pdf format. A file that everyone can access, but is a pain in the butt to edit and modify. If you designed your file with good topology then you won’t have a problem. If you don’t know what good topology is then you most likely used a CAD program. And there are two reasons why I hate when CAD programs export a file as an .stl.
Problems With CAD to STL Conversion
The conversion is almost always horrible. The geometry is often crazy and the model is changed in the conversion. For example a smooth edge gets changed so that multiple edges make a smooth edge.
If you wanted a smooth edge you will have to manually correct the conversion by adding more geometry. Furthermore the conversion creates a non-uniform mesh. One face of the mesh might be 1000 times larger than another face. Triangles, squares, and polygons appear. The non-uniform geometry makes it almost impossible to edit and deform.
Basically it looks something like this. This is bad because the geometry is not uniform.
If you wanted a smooth edge you will have to manually correct the conversion by adding more geometry. Furthermore the conversion creates a non-uniform mesh. One face of the mesh might be 1000 times larger than another face. Triangles, squares, and polygons appear. The non-uniform geometry makes it almost impossible to edit and deform.
Basically it looks something like this. This is bad because the geometry is not uniform.
How to make a better stl conversion? (Via Blender )
Basically our goals in doing this are:
- Make the geometry uniform
- Keep our geometry count low
- Keep the original Shape (note that the shape may slightly alter)
As you can see there is little changes to the cars below. We want to find a point where our geometry is low, but we still have a good shape. And as
1.) Remesh Modifier
This is probably the easiest for people with little blender experience, however it often creates an excessive amount of faces. If you are wanting to add something with fine detail such as a texture the excessive geometry will most likely be needed. This can be done with the DEFORM MODIFIER. The following are the most important aspect of the tool.Sharp / Smooth / Blocks
If the model has a sharp edge use sharp. If it doesn’t then use smooth. Or if you want like an 8-bit looking thing use blocks.Octree
This is similar to subdivide, the higher the number the better the result, but the slower the program will run.Then you will get something better like this. This has more uniform geometry but perhaps overkill. If your computer can handle this, then it is okay to stop here. Otherwise see the next steps.
2.) Decimate or MeshLab
If your model is simple enough you can use blender's decimate modifier to reduce the geometry. and get something like this. Which is far from ideal, however somewhat better that when we started.
However the better option is to export your remeshed model into a program called Meshlab that can handle the decimation better. Under Flilters -->Meshing, Simplification, and Reconstruction you can apply filters such as Surface Reconstruction Poisson, Quadratic Edge Collapse, Uniform mesh resampling, tri to quad, etc. until you are happy with your results. And you will get something like this:
From here you can work easily with your model. Not that the model will change
OR...
Manually
Depending on how bad the conversion is and what you want to modify you may be able to simply change the model by rearranging the geometry and using the KNIFE TOOL to add more geometry. Depending on the situation this can be the easiest method as the other methods often may not work without a lot of geometry.However there is a more time consuming way called Retopology. Here is a good video on how to do this:
http://www.youtube.com/watch?v=icqPZnD_3lA
Shrink Wrap Modifier
This tool takes the geometry of one mesh and then places it in the for of the second mesh. This method is fairly simply however it seems to work on simple shapes and not well on more complex shapes.Can you convert from an stl to a CAD format?
Now if you try to go the other way, from an .stl to a CAD format such as an .iges, it is impossible. I have searched a great many hours for a program that can convert an .stl into a format that can be used in a CAD program and all I have found is dead ends. If you find something that can and you have personally done it, please inform me.The reason why you would want to do this is because most files downloaded from the internet are in stl format. If I wanted to add something of a specific size such as screw holes, it would be easiest in a CAD program. A person could then take any model and easily design it.
Please leave a comment.
And as always, thanks for visiting
3D Printing Ninja
3DNinjaneer@gmail.com
Category: Basics, Blender, Decimate, Design, File Conversion, Intermediate, Meshlab, Remesh, Surface Reconstruction, Tools, Tricks & Tips, Trouble Shooting
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