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Mechanical Design

CAD File Formats and How to Export Them for 3D Printing

There are a lot of CAD (computer-aided design) file types out there, each with their own names, formats, and parameters. From STEP files, to STL files, to IGES, and more, it can be difficult to differentiate between them all. This post will help you understand the difference between these file types, and which file is best for uploading to a 3D printer or 3D printing service.


Overview: CAD Model Types

Before we review the steps for CAD file preparation for 3D printing, here's a brief overview of different CAD model types.

One very basic way to distinguish between CAD models types is by breaking it into these two groups:

  • Parametric (solid)
  • Mesh (NURBS)

A parametric model is one which consists of solid blocks or vectors that have both magnitude and direction. A mesh model, on the other hand, is a collection of small triangles that make up a surface.

If you compare these two types of models to a 2D image file, a parametric model is like a vector file (.AI, .SVG, .DXF) while a mesh model is most similar to a pixel image (.PNG, .JPEG).

Just as a pixel image (.PNG) approximates a vector file (.AI), when converting a parametric model to a mesh model, a mesh file (.STL) approximates a parametric file (.STEP).

Pro Tip: If you’re looking for an in depth read about mesh modeling vs solid modeling, check out this article.


Best File Types for 3D Printing

Now let’s dive into how you can prepare and export your CAD models for 3D printing and which file types we recommend.

There are 3 main file types used in 3D printing:

  1. IGES or IGS (Initial Graphics Exchange Specification)
  2. STL (Stereolithography or Standard Tessellation Language)
  3. STEP (Standard for the Exchange of Product model data)

Third Choice: IGES/IGS Files

This file type was created by the US Air Force and was used for exchanging CAD geometry. It was later adopted by the American National Standards Institute (ANSI).

Main thing to know about this file type is it’s an older, unsupported specification so it will never be updated or changed. Hence, why this is the third best choice for 3D printing files.

Second Choice: STL Files

There are two types of STL files:

  • ASCII: large files size and not recommended
  • Binary: compressed file, which is better for saving and sharing

STLs were originally developed by 3D Systems specifically for additive manufacturing and are widely known as the industry standard. However, STL files have several shortcomings. For example, there’s no associated units and holes or gaps (watertightness) can cause issues when producing parts.

First Choice: STEP Files

There are 2 main types of STEP files:

  • AP203: originally created for the aerospace industry
  • AP214: The newest standard which was originally created for the automotive industry

In our opinion, STEP files are the best file format for transferring CAD data. STEP files carry all of the parametric data required so manufacturers can easily read the size and geometry of the part you need.

Pro Tip: STEP AP214 will save the colors and layers in your CAD program when exporting as an STL. When saving for multimaterial prints, we prefer this standard since it helps to distinguish the different solid bodies.


How to Export an STL File for 3D Printing

It’s easy to run into problems when exporting an STL file. Since a lot of people do use STLs we’re going to point out a few important considerations and then walk through specific exportation steps for the most common CAD programs.

Resolution

The most important consideration to take into account here is the resolution of your model. If you try to export an STL with a low resolution, your model will look faceted and if you export an STL with too high of a resolution, your model will become very large and difficult to share.

sphere comparison CAD model 3D printer files
Left: parametric (.STEP) Center: low resolution mesh (.STL) Right: high resolution mesh (.STL)

Two Main Program Settings

There are two main settings to consider with every CAD program:

1. Chordal Tolerance or Deviation

This is the maximum distance between the surface of the original design and the surface of the STL triangle created.

2. Angle Control

This is the allowable deviation between adjacent triangles. You should think about approximating a curved surface with lots of flat triangles; the more shallow the angle, the closer the approximation is to the curved surface.

Specific Settings by CAD Program

Solidworks

  1. File > Save As
  2. Set type to STL
  3. Click on Options
  4. Set Deviation to 0.0005in and the Angle to 5 deg

Inventor

  1. File > Save Copy As
  2. Types > STL
  3. Click the Options button, and choose the High detail level
  4. Save

Rhino

  1. File > Save As
  2. Select File Type to STL
  3. Select File Name > Save
  4. Select Binary
  5. Select Detail Controls from Mesh Options
  6. Set Max Angle to 20, Max aspect ratio to 6, and Min edge Length to 0.0001
  7. Hit OK

If you're ready to start uploading your design files for 3D printing you can visit Fictiv for an online quote in minutes.

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