3D Modeling

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Introduction

This is a page in progress to describe 3D modeling, with the intent of printing the model on a 3D printer - not for CNC fabrication, though models are used for CNC fab.

In order to make things from either 3D printers (or CNC routers/mills that have 3 or more degrees of movement), you need a 3D model.

While your first experience with one of these machines may use an existing test model or one you've downloaded from a site like Thingiverse, eventually you may want to create things of your own.

The general workflow for 3D modeling and printing is:

1. Model the part

2. Turn the model into instructions suitable for the machine (printer) to print it.

3. Send the instructions to the machine and fabricate the part.

This page will only deal with the first step; how to model a part, and it will not cover how to use specific software.

Machine Requirements

Regardless of what modeling software the model you use, there are a few considerations you must make:

Maximum size. The part may not be larger than the printable area of the printer you are using. Larger items can be made by dividing your object into components that are assembled after printing. For example, the LulzBot at PS1 has a usable print area of 200mm x 190mm x 100mm (7.9in x 7.5in x 3.9in)

Minimum size. Parts must be large enough to resolve, large enough for the print-head to extrude something that holds together.

STL files for parts must be manifold. Manifold is a term that means the surface of the part is contiguous and complete, and with regards to 3d printing, also not zero thickness. Imagine a soccer ball shape: that would be 'manifold,' but if the soccer ball were missing one polygon, it would not be manifold. In order to print such a shape, either the walls of the part need to be thickened, or the gaps or holes need to be patched. Some models created with common software, particularly SketchUp, can be impossible to print without serious repair and reworking, because the models include many holes or gaps and are often composed of zero-thickness planes rather than solid shapes with volume. 'Manifold' is also referred to as 'water-tight.'

Your model should be "watertight" (the mesh has a mathematically determinable interior), correct normals, and a manifold topology. Shapeways has a nice tutorial explaining this.

Free 3D Modeling Software

Here is a very out-of-date list of some free 3D modeling applications: 25 free 3D modeling applications

All software suggestions in this section are open source, and are available for free.

  • For individuals new to 3D modeling software, Blender is a good tool for designing models for 3D printing, as well as for debugging fussy models (Blender can highlight the parts of a model which make it non-manifold). Blender recently had a total overhaul of its codebase and user interface, and has become quite user friendly. Additionally, the Blender foundation produces and sells video tutorials. The video tutorials are distributed on dvd data disks, but are creative commons licensed, and so you may legally download them for free online. The videos are created by artists, and cover a wide array of topics from basic usage of the program, modeling techniques, and the more advanced capabilities of Blender.
  • Meshlab is an open source tool for repairing 3D models.
  • FreeCad is a general purpose feature-based, parametric 3D modeler for CAD, MCAD, CAx, CAE and PLM, aimed directly at mechanical engineering and product design but also fits a wider range of uses in engineering, such as architecture or other engineering specialties.
  • OpenSCAD is a different take to 3D modeling. OpenSCAD is a programming language that generates parametric 3D models.

Non-free 3D Modeling Software

AutoDesk Fusion 360 is not open source but is essentially free to makers and education users. To get the free copy: download trial, when trial is up and it asks for license number there is a checkbox to say you will not make money on the products you make. (citation: personal experience) You can buy a single-user license for Fusion 360 pretty cheap too, or wait for sales that have been up to 90% off. Generally though, the free download covers almost everything. Expect to see paid extensions and features in the future, I bet. There are meetups at PS1 to support Fusion 360. http://www.autodesk.com/products/fusion-360/overview

AutoDesk Inventor may be available as an educational trial, for members of PS1. (cite?)

Designing 3D Models

There are several types of modeling operations. Some software manipulates simple shapes like spheres or cubes, pushing and pulling on control points until the desired shape is achieved. Other software uses 2D sketches to extrude or rotate shapes. Some software is intended to design parts that have precise dimensions, like CAD programs, while other software is more suitable for designing free-flowing shapes or character modeling. If the software you are attempting to use isn't letting you make what you need, you should consider other applications.

Saving a copy of the file for printing

In addition to the native file format (whatever your 3D modeling program uses) 3D models for printing should be saved or exported for printing, in the STL format (binary or ascii).

After the part is modeled it needs to be turned into commands the 3D printer can recognize, a step called 'slicing' since it turns the solid shape into a series of paths and printer commands to move and start and stop the extruder, that build up the part layer by layer. The next step in 3D modeling, then, is to save the part in a format that the slicing software can recognize. Common formats include STL, but may vary depending on the specific software and workflow you will be using.