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It starts with a Design File: Intro to Modeling for 3D Printing

Before you can print, you need a 3-dimensional design file. The last twenty years has seen ongoing evolution in the sophistication of the computer software for professionals, but more importantly, it has become accessible by non-professionals. There are multiple open-source programs, programs that leverage cloud computing rather than rely on a powerful personal computer, as well as systems designed to be operated on a mobile phone. This is a far cry from the desk sized mainframe system with their dedicated operator seen in the 1970’s and 80’s.

While there are many variations, you can organize CAD (Computer Aided Design) software into three basic types: wire-frame, surface and solid. While the three fundamental types of modeling system roughly follow the evolution of the software’s capabilities, all three are still now used for different applications.

Wire Frame looks just like it sounds, a “frame” of lines connected by points. The file contains information about the locations of all the points (vertices) and edges in space coordinates. The entire model is a collection of edges, there is no skin defining the area between the edges. While not exactly “pretty”, it is the most computationally efficient type of model. It is useful for designing simple parts to make on older machining equipment, and excellent for running simulations. Because they have no surfaces or volume, these models can NOT be 3D printed.

The Surface model is essentially a wire frame with a skin stretched over it. This type of model is very common in visual design applications, where only the surface needs to be shown, and computational needs can be reduced by eliminating the interior. That power can then be used to create incredibly detailed, photograph-like images of the model (commonly referred to as “renders”). Because they have no volume, these files can not be directly 3D printed. However, if the “skin” is completely closed, with no openings between the interior and exterior of the model, it can generally be converted to the next type of model: the Solid.

The Solid has all the advantages of surface models (uniqueness, non-ambiguous, realistic, surface profile) plus volumetric information. Mass and volumetric properties of an object can be easily obtained; total mass, mass center, area and mass moment of inertia, volume, radius of gyration, etc. However, this additional information comes with a cost, it involves much more intensive computation than wireframe and surface modeling. These CAD systems could only be run on high performance, professional computers.

While the basic functions of 3D modeling systems have changed only incrementally, the context for its use has changed dramatically. With the popularization of 3D printing, there is a whole new amateur user demographic using the tool. Cloud computing now allows inexpensive and computationally limited machines (even smart phones) to operate solid modeling software. The sophistication and functionality of “freeware” (open access software) has continued to evolve to compete with professional systems. At the same time, design software is struggling to keep up with the complex geometry possible with 3D printing. In 3D printing, a complex shape and a simple one are equivalent in difficulty to produce. In the design software, however, a complex shape file may exceed the computational capacity of the software or the operating system. Some 3D printers can change the color, material and mechanical properties of each individual point within a part, and yet there is no commercial design software that can model this directly in a design file.

If you are just starting out with 3D modeling software, look at what you want to do with it. If you are doing a very complex mechanical analysis, go with a wireframe system. If you want beautiful images, use a surface based software. If you are 3D printing, make sure that whatever you use, it gives you a Solid at the end. 

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