How, When and Why to Use Class A Geometry in Fusion 360

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“There are no beautiful surfaces, without a terrible depth.” – Friedrich Nietzsche

Class A geometry was originally an automotive industry term that refers to a surface, or series of surfaces, that have curvature and tangency alignment. It’s an ideal method when working on the aesthetics of cars, but I’m here to tell you that in today’s day and age, you’re probably using class A more than you need to. (Put the pitchforks down, I see you in the comment section primed for a rant about the glory of class A geometry, but I assure you it isn’t under any threat.)

In all honesty, I’ve been avoiding writing this blog post for a while. In CAD terms, I’m an old dog. I’ve been doing this since I was 16 years old, and I come from a background that is obsessed with geometric perfection. In the past ten years of my life as a professional, however, I have only used class A once in a real-world situation, and that was last year while working on the Volkswagen project.

volkswagen-generative-design-autodesk-fusion-360

Credit: Volkswagen.

Class A geometry has become a benchmark that industrial designers use to determine if their tool is good enough to use, but what a lot of people fail to remember is that in most manufacturing situations, your class A surface won’t make it into the physical world. We simply don’t tool things for that level of tolerance.

“But what about rendering!” Well, let’s be real: editing images is faster, and most clients prioritize delivery time over that last percentage of perfection. Even if you are a CAD master, it only takes a beginner level of skill in Photoshop to edit your renders to get that pixel-perfect look. Unless you work in an industry or on products that will explicitly use class A geometries at a physical scale (such as a car body,) there is little need to produce class A geometry.

For those times when class A geometry is necessary for a project, however, let’s dive into how we do it using Fusion 360.

Prerequisites

First, let’s take a look at some essential tools you will need to know at least at a fundamental level before getting started.

Parametric modeling 3D sketching At least have a fundamental understanding of how to use this environment to create 3D sketches. Surface modeling Check out classes here. Silhouette split Silhouette split is located in the toolbar. It takes any construction plane that intersects a body and then gives you the edges at the outermost point of that object based on the orientation of your construction plane. Networking If you’ve used tools like Alias, or other surfacing modeling tools, chances are you’re familiar with the principle of network surfaces. In Fusion 360, the process of producing network surfaces is already built into other tools and is not explicitly called out. We call this “horizon modeling.” Horizon modeling: In the example of the tetrapod, or any other class A geometry problem, the most essential element that makes up the surface are the edges. Making sure normals and tangents are in place ensures a class A

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