Blender is a fantastic software for modelling, animation and sculpting; however importing geometries from a .step file can be a pain. This can be useful if you have a CAD file built in Fusion 360, Solidworks, FreeCAD, if you download a CAD file online from GrabCAD https://grabcad.com/library or you want to control the density and quality of the STL mesh. Many geometries are available as .STEP format and not importing directly from the interface can be a problem. Another issue is that many times you don’t control the type of mesh present in a STL format, which can generate a heavy model due to a very large amount of nodes or incorrect refinement zones. In this article I will try to list the options you have available for performance, speed and easiness.
INTRODUCTION TO BLENDER, STL AND STEP
APPROACHES TO CONVERT from STEP TO STL
EASY FREECAD OR OPEN CASCADE STL EXPORT
ADVANCED GMESH STL MESH EXPORT
1. INTRODUCTION TO BLENDER, STL AND STEP
Blender is a free and open 3D creation software. I simply love this software and with it I create fantastic product images and animations, but it’s possibilities are endless. Take a look at https://www.blender.org
Blender imports many formats but doesn’t import a typical and very open format like .STEP. This format is very common on CAD software like Fusion360 and FreeCAD. Blender however allows to import an .STL file and so for that reason it is needed to convert our geometry to STL.
An STL file is defined in wikipedia in detail in https://en.wikipedia.org/wiki/STL_(file_format) where basically it is a surface triangular mesh of an object. The smaller the mesh (size of triangles) the better it will represent the object but also it will be more heavy to deal with it (increase CPU load to manipulate or view it).
A STEP file is defined in wikipedia in detail in https://en.wikipedia.org/wiki/ISO_10303-21 where it basically is an ISO 10303-21 rule set to represent 3D objects. Almost all 3D modellers provide conversion to this data format.
For those who like to create their geometries on CAD specific software makes it relevant to be able to use these geometries with Blender to create 3D renderings or animations.
2. APPROACHES TO CONVERT from STEP TO STL
A. EASY FREECAD OR OPEN CASCADE STL EXPORT
The process of conversion in FreeCAD is actually very simple. Open the .STEP geometry.
After opening the .STEP file we need to select the geometry we opened. To select the geometry you will need to click on the geometry name in the left tree view. The geometry will get highlighted. Then Click export.
In the export menu you should have the option to convert to .STL. This task is pretty straightforward with FreeCAD.
An alternative way is to use OPEN CASCADE – CAD assistant which is a free tool that can be downloaded for free.
B. ADVANCED GMESH STL MESH EXPORT
For the Hardcore user a standard autogenerated mesh might not be enough. Here let’s explore an option that gives us more control of the final generated mesh. It is important to note that when we import the .stl mesh on certain software the mesh isn’t visible by default. With gmsh we can control how the mesh is generated. We can even build a mesh out of Hex elements and then convert to STL for a triangular surface mesh. The main idea to retain is that you gain control over what is done in this process.
The resulting Blender imported file can be viewed importing an stl file in blender.
The amount of detail to include in the Blender model is now in your hands as it should be.
FreeCAD and OPENCASCADE CAD assistant are very easy to use and the conversion process to .STL has no complications.
Gmsh advance mesh creation is also very simple to use and with it you gain an extra control layer to generate the model conversion you require. More quality, or more detail is now an option to explore.
Today creating an .STL file is very simple, comparing to an attempt I made 3 years ago. At that point in time the solutions proposed weren’t as mature and as they are today.
Things I would like to see improved in gmsh.
A more point and click interface. What I think is the only point missing in gmsh to become a standard software for simulation, modelling, and more… is a point and click interface. The ability to select lines, faces and volumes with the mouse. This is useful if you wan’t to improve the mesh on that specific edge or face.
The ability to slice the solids. Slicing the solid to be able to create zone that can be more refined than others, instead of applying a single rule to the whole geometry.