Originally Posted by
DrDucati
Yes, STL files are composed of triangular meshes. But that is currently the only way to describe complex organic shapes for the purpose of fabrication, whether stereolithography, 3D printing or CNC milling.
There are two worlds of 3D: mechanical design (CAD) and organic modeling. CAD software (SolidWorks, Pro/Engineer, Alibre, etc.) is geared toward simple parametric shapes (flat surfaces, cylindrical holes, simple rounds, etc). The most commonly used file format for machining (IGES) is suited for these types of features. IGES files can be converted to STL files for stereolithography or 3D printing but individual feature information is lost.
Organic modeling, on the other hand, is geared toward complex non-parametric shapes (people, animals, trees, etc.). Modeling software (maya, modo, zbrush, etc.) is primarily used for visualization (movies, advertising, video games). The underlying geometry and the most commonly used file format for geometry exchange (OBJ) is composed of polygons (including triangles). OBJ files can be converted to STL files because the geometry is similar. OBJ files are not usually converted to IGES files because you can't take polygon data and extract simple features like flat surfaces, cylinders, rounds, etc.
So, although STL files may not be ideal for CNC milling, they are the only game in town for organic surface models. Thankfully, CNC programs like SprutCAM, Mastercam, etc. can create tool paths from them. So we can fabricate organic shapes on our Tormach milling machines. Cool!