How Normals and Facets Affect 3D Modeling

In order for a 3D printing to be accurate, least of all successful, there should be a combination of correct elements in the engineering process. This requires the 3D design to be solid, and watertight.  Facets and normals are an integral part of this process. Rapid prototyping creates a mesh of tiny triangles. These triangles are laid over the surfaces that define the shape of the object. The triangles intersect completely, without overlapping or holes. It is only when their geometry translates into a solid model, that you have a successful 3D replication.  To better understand this process, here are the definitions of facet and normal.

What is a facet?

A facet the triangular element used to estimate the exterior of a model. Thousands of facets combined are required for complex 3D models. All facet data is stored in an STL file.

Architectural 3D Print Job with Normals
Anything in black will not print and is considered a normal

What is a normal?

A normal is often referred to as a surface polygon.  One facet normal is made up of three nodes and one outward normal.

Because facets and normals make up the entirety of a 3D model’s surface, naturally they play an important role in overall design structure. Therefore, if there is an irregularity in the design, the 3D model will be substantially affected.  Inverted normals and degenerated facets are two examples of what can happen if your model’s geometry is engineered incorrectly.

Normals become inverted when they are not properly oriented, causing a gap or hole in your project. Facets degenerate when improper import or export settings occur, when there are limitations in the .stl export, or if there are errors in the overall mesh operations. Fortunately, neither one of these problems is considered critical, requiring easy-to-implement solutions.

Earlier, this article stressed the importance of a solid, watertight model for an effective 3D print to occur.  It is imperative that a model does not have any open or unconnected seams. 3D models necessitate that all details are surfaced and completely connected to adjacent geometry.