Mesh vs. NURBS: Which 3D Model Is Best for 3D Printing?

When designing a 3D object using a CAD program, popular modeling programs use either polygon mesh or a Non-Uniform Rational Basis Spline (NURBS) to describe the object. When creating a file for 3D printing, most CAD programs convert the file to STL format (which converts it to a triangular polygon mesh). If you're wondering if you should create the object with mesh or work in NURBS and then make the conversion, we compared both to help you decide.

Overall Findings

Polygon mesh renders 3-dimensional items on the computer. Because of this, it is the format used by STL files for 3D printing. When using triangles to create 3D shapes, you create approximations of smooth edges. You will never achieve the perfect smoothness of an image initially created in NURBS, but the mesh is easier to model. You can push and pull on the mesh to move it and achieve the same results each time because it is not calculating mathematical averages of points.

As far as computer modeling goes, NURBS creates the smoothest images. It also creates accurate models with even edges that are not pixilated. For engineering and mechanical applications, NURBS-based computer rendering is preferred to polygon mesh-based programs. Generally, when you scan objects into a CAD program, those objects are initially scanned using NURBS.

Compatible Programs: Free and Premium Versions

Both polygon mesh and NURBS users have a variety of free, freemium, and commercial software programs to use. And many programs have both options built-in. In the free software Blender, to make a movie, for example, you can make characters with polygons but use NURBS for the environment to get natural-looking terrain with organic curves.

Other major NURBS programs include Autodesk Maya, Rhinoceros, and AutoCAD. Still, these also include polygon mesh. The SketchUp basic, free version only supports polygons in its built-in tools. The Pro edition supports extensions that approximate NURBS processes like smooth curves.

Whichever tool you choose, you don't have to spend hundreds of dollars to make models. However, some of the more powerful software does come at that kind of cost.

Ease of Use: Mesh Models and Prints Faster

NURBS is better at rendering curved surfaces, although approximations can be made in a mesh model by increasing the number of sides in the polygons.

NURBS has its limitations. Because it is a 2-dimensional rendering form, you need to create patches that you piece together to make a complex 3-dimensional shape. In some cases, these patches do not fit together perfectly and seams appear. It's crucial to look carefully at an object when designing it and make sure the seams align perfectly before you convert it to mesh for the STL file.

For beginners, mesh polygon programs are a good starting point to learn the basics of 3D modeling. It doesn't take long to get to a basic model.

3D Printing: Polygon Mesh Is Faster

If you're modeling for the purpose of 3D printing, polygon mesh has an advantage over NURBS. A NURBS file can't be converted directly into STL format (the file type that slicing software uses to generate the instructions for the printer). There's an extra step of converting it to a mesh first.

When you work in NURBS and convert the file into a mesh, you can choose the resolution. High resolution gives the smoothest curves in the object being printed. However, high resolution means you'll have a large file. In some cases, the file may be too large for the 3D printer to handle.

Aside from finding the perfect balance between resolution and file size, there are other cleaning methods to reduce the file size. For example, when you craft an object, don't create inner surfaces that will not be printed. One way this could happen is if two shapes are joined together. Sometimes the join surfaces remain defined, even though, when the surfaces print, they won't be separate surfaces.

Overall Findings

The 3D design program that you are most comfortable with will most likely have an option to export a NURBS or mesh file to an STL or another 3D-printing format.

Whether you initially make your object using NURBS or mesh depends on your preference. If you want an easier program in which you won't have to convert, starting in the mesh will be the best option. If you want a program that gives you perfect curves, choose one that uses NURBS.

Other great resources for understanding different model formats come from 3D printing service bureaus (such as Sculpteo and Shapeways). These firms handle file types and formats from most 3D design programs. They often have great tips and suggestions to get files to print right.