Whether you are using the dedicated Mesh2Surface plugin for reverse engineering, or open-source tools like Blender and FreeCAD, remember the golden rule: Understanding the "why" behind the crack transforms you from a frustrated modeler into a master of hybrid geometry.
NURBS surfaces are defined by polynomial equations (degrees 3, 5, etc.). They are mathematically smooth. Meshes are linear approximations (flat triangles). When you tell a computer to stitch a flat triangle to a curved polynomial, the triangle can only touch the curve at specific points. Everywhere else, there is a microscopic gap. Aggregated over thousands of vertices, this becomes a visible crack. mesh2surface crack