Adjusting the surface tolerance allows for fine tuning of the lattice pattern at the surface.

How does this fine tuning work? Every lattice begins with a compilation of polyhedra that creates the lattice pattern. The performance value of a Carbon Design Engine lattice is in its conformity to the design space.

In order to conform to the surface boundary, the Design Engine must adapt the lattice pattern to meet the surface conditions. While polyhedra are 3-dimensional, the surface ultimately conforms a polygon shape on its face.

Let's use the tetrahedral lattice type as an example, which consists of triangular faces. When the tetrahedral pattern is built, the 3-dimensional tetrahedrons don't necessarily conform exactly to the surface of the design space. Some of the triangular vertex points protrude or fall short of the surface by a slight margin.

Surface Tolerance is the margin by which the vertex is allowed to vary from the exact surface boundary.

What this means in practice is that a low tolerance (or small margin) leads to the formation of smaller tetrahedrons to conform to the surface more closely, leading to a less uniform surface pattern. A larger tolerance (or large margin) will keep the tetrahedra more uniform.

The resulting pattern, is projected onto the actual surface boundary to create the lattice. This means the resulting lattice does not differ in overall size and shape.

The most effective values for surface tolerance are

The default surface tolerance is on the low end.

The results of surface tolerance are ultimately subjective. The best results balance pattern uniformity at the surface with depth of pattern.

In the above example, the results of the 0.3 and 0.4 * cell size patterns create a nice uniformity.

The 0.5 * cell size solution manifests a shallow depth of pattern at the surface that begins to lose some of the gains in uniformity. At the surface, there are struts that appear broken. As we look at how those struts connect to the pattern below, we see that they are not broken at all, but rather just connecting to the 3-dimensional pattern at a very shallow depth. The eye may not read the pattern as uniform with other struts so close to the surface.

For a single zone lattice, surface tolerance generally drives the pattern closer to the type's primary pattern.

Hybrid lattice types have a great deal of complexity in how the pattern appears on the surface. Using surface tolerance provides a degree of fine tuning that can provide interesting variations in the pattern.

The example below is a difference of just 0.1 in the surface tolerance value.