There are many different ways to export .stl files for 3D printing and SLS printing. This post is a guide that clarifies the process so that users can optimize their settings for specific needs.

What is STL?

The STL format is the most widely used format for additive manufacturing. STL stands for Standard Tessellation Language or STereoLithography. The format describes a 3D object’s surface geometry without any color, texture, or other properties. This format uses a series of interconnected triangles to recreate or reproduce a 3D model’s surface geometry. The more triangles used, the higher the model’s resolution.

The importance of .stl file formatting

Many websites that publish 3D models use the STL format. Thanks to the format’s simplicity, STL files are fairly small. They may lack the precision of other formats, but most 3D printers are similarly limited in the level of detail they can reproduce, so it doesn’t really matter. The format makes file portability possible, which is a significant advantage for most manufacturers in the AM space.

STL has become widely accepted as the standard format for prints intended for additive manufacturing and manufacturers. 3D printers are therefore being designed to work with the format. Furthermore, most 3D modeling software is designed to open STL files.

The format also serves as an interface between 3D modeling software and 3D printing hardware. Full 3D models created with CAD software can be too complex to easily share online. They may also be difficult for 3D printers to read. By converting these files to STL, the model is simplified and thus easier to understand for a 3D printer’s slicer software, a software that converts the model into layers, which print consecutively.

Settings for exporting STL files for 3D printing

Below are some of the most important settings for exporting STL files for 3D printing. These settings will give you appropriate file sizes, as well as high-quality prints.

Units for STL export

STL files are unitless. They do not retain information about a model’s actual dimensions when the file is saved in one application and then opened in another. This can cause problems when exporting files to a 3D printer. Therefore, it is important to specify the correct unit for a model when it is imported into a particular program. If we first design a model in millimeters, and then open it in inches, it will be about two-and-a-half times too large. Wematter’s SLS 3D printer Gravity, for example, uses millimeters as its unit to specify the size of the model.

ASCII or Binary

Since STL files are used extensively with 3D printers, it may be helpful to think about how the file stores information to make it as easy to read as possible for the machine. STL files can store information in two different ways, either through binary encoding or through ASCII encoding. Binary encoding is best for 3D printers because it is only made up of ones and zeros, and results in smaller files that are easier to share. ASCII files, on the other hand, are based on text. They are visually easier to read, but they generate larger files and take longer to load. These heavier files are also unnecessary in that they do not provide better print quality, since too small detail cannot be printed.

Resolution

We learned above that the STL format uses a series of interconnected triangles to recreate the surface geometry of a solid model. As the resolution increases, the program uses more triangles which creates a smoother surface for the 3D model, but also increases the size of the STL file. If you export the model in too low a resolution, the model will have visible triangles on the surface when printed. Often, this is something you want to avoid, but you can use it to create low poly models with a digital look.

The pictures above show a 3D model of a ring in 3D Builder with a resolution of 768 and 20,000 surfaces, respectively.

Choosing the right export parameters

The resolution of an STL file can be changed by adjusting tolerances in the CAD software. Each program has its own way of specifying this, but most use two parameters that we choose to call chord height and angular tolerance. Chord height specifies the maximum distance the software will allow between the surface of the original 3D model and the surface of the STL file. A minor deviation will help to more accurately represent the curvature of the surface. Our recommended value for chord height is 1/20 of the thickness of the 3D print layer, and never less than 0.001 mm. The illustration above shows the maximum distance deviation (chord height).

Angular tolerance limits the angle between the normals for adjacent triangles. The default value for this is often 15 degrees. Some software also specifies this tolerance as a value between 0 and 1. Unless you need a higher setting to achieve a smoother surface, we recommend the default value of 15 degrees or 0. The illustration above shows the angular tolerance.

Wematter Deep Space and file handling

Conversion from ASCII to Binary coding

In some cases, you may forget to export your file to binary code, and in other cases it is simply not possible to choose this. In these cases, Wematter’s Deep Space software can convert from ASCII to binary encoding and successfully read the file.

When uploading an ASCII-encoded file, the status message above shows that conversion is being performed.

File size

When it comes to files exported to a 3D printer, larger files are not necessarily better than smaller ones. The larger the files, the longer they take to upload into the Deep Space interface. This can make these files impractical to work with. In that case, it is better to convert them from the beginning using the settings above, so that they are not larger than necessary for the quality required by the prints. However, if an oversized file is loaded into the program, the files will compress in the background to be easier to handle.

Repair tool

The Repair tool is a piece of software within Deep Space Cloud Services that can repair broken files before further processing. If an incomplete file is uploaded with a model containing gaps, the program will try to fix these gaps before the object is placed in the scene. For example, the tool will scan for holes in the polygon mesh, walls without specified thickness, or places where triangles don’t connect in a proper way.  It then tries to solve these problems using different algorithms to attain a printable shape.

When uploading a broken file, the status message above shows that Repair tool is working to fix the file.

Quick guides for exporting STL files for 3D printing from different programs

Inventor: How to export .STL for 3D printing

1. From the Tools menu, select Rebuild All. This ensures that the design data contains recent changes, and that it is not corrupt.
2. From the File menu, select Save Copy As
3. In the File-type drop-down, select STL Files
   
4. Click Options
5. Select High (for the highest surface quality) and click OK (the “High” setting will also produce the largest file size).
   
6. Make sure to select Binary, and that Units are in Millimeters prior to clicking OK

Catia: How to export .STL for 3D printing

1. Click on Generate CATPart from Product in the Tools menu
   
2. Click on File and Save As
3. Set Save As file type to STL

Solidworks: How to export .STL for 3D printing

1. Click on File, and Save As
2. Set Save As file type to STL
3. Click on Options, Resolution, choose Fine or Custom, and click OK
   

Sketchup: How to export .STL for 3D printing

1. In SketchUp, creating STL files directly within the program may not be possible. An extension for .stl must be downloaded first in order to export STL files.
2. Download and install the SketchUp STL plugin
   
3. Choose Export to DXF or STL from the Tools menu.
4. Choose Millimeters as the unit, and Binary as the file format for the model.
   

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