Are you troubled by poor print quality while 3D printing STL file? Are unmanageably large 3D files getting created when the STL file is exported in high resolution? Don’t worry. This post would act as a guide to help you understand the STL file type and the detailed steps for exporting the file format for 3D printing. Let us first start with a brief introduction.

Coming to the origin of STL files, it was first developed in the late 1980s by 3D-Systems. It was mainly created to get the CAD data converted into 3D print-ready files. And today, it has become successful and is a widely used format not just for 3D printing but also for the purpose of rapid prototyping and computer-aided manufacturing.

STL or Standard Triangle Language file is considered industry standard for printing on 3D printers. A sequence of triangles is used for representing the solid model’s surfaces in STL. Contemporary CAD (Computer Aided Design) programs permit export of their respective proprietary file formats in STL type for ease of 3D printing. Conversion of the 3D models into G-Code machine language is done through ‘slicing’ for rendering the STL files and make them print-ready.

What is STL File Format?

The STL file format basically stores information about the three-dimensional models. Here, the information is related to the surface geometry rather than the common attributes like color and texture.

The STL files are generated at the end of the 3D modeling process. This process is often carried out with a CAD or computer-aided design program.Ever since the beginning, it is supported and adopted by many CAD software packages. And now, it is widely used for 3D printing, rapid prototyping, and CAD manufacturing.

The extension of this file format is .STL. The abbreviation is usually considered to be STereoLithography. Even so, it is sometimes referred to as Standard Tessellation Language or Standard Triangle Language.

How to export STL files for 3D Printing?

For accurately exporting 3D print ready models into STL files for convenience of 3D printing, you need to follow the steps mentioned below. Adhering to them would also lead to reduction in the 3D printing related expenses.

  • Get a clear view of STL resolution

    As stated earlier, a sequence of linked triangles is used by the STL format for recreating a solid model’s surface geometry. As the resolution of STL files is increased, the number of triangles used would also go up in number. This would lead to a better approximation of the 3D models’ surfaces. However, the STL file’s size also increases.

    When the model is exported in very low resolution, the triangles would be visible on the surface of the model after printing. This is something you won’t want on your model’s body. But, you can utilize the digital look for creating ‘low-poly’ models. It is not desirable that you increase the resolution after a certain degree. You would not get any new benefit. Extremely minute details cannot be captured in 3D prints. However, such an increase would lead to unnecessary enlargement in the file’s size. Consequently, large files would pose problems in handling and processing.

  • Select appropriate parameters for exporting

    By changing the tolerance within CAD program, the resolution of STL files can be modified. If you are not sure about the tolerance level, go for ‘high’ preset. This is the best bet when you want to generate STL file that can be conveniently 3D printed.

    STL resolution is specified in different CAD software in differing manners. However, 2 parameters are common to all packages i.e. angle and chord height.

    Chord height represents the maximum distance between original CAD 3D model’s surface and the STL file’s surface which is allowed by CAD software. The surface curvature can be represented in highly accurate manner by keeping the chord height smaller. Chord height should be ideally kept at 1/20th of the thickness of 3D printing layer. The value should never go under 1 micron or 0.001 mm. The resultant STL file would be very accurate for applications that can help in optimum 3D printing. The print quality would not suffer if the model is exported in smaller tolerance value. This is because 3D printers commonly available are not capable of reproducing extremely high detailing level.

    The angular tolerance is used to keep the value of angle within adjacent triangles’ normals. It is set at 15 degrees by default. In some CAD program, you may come across this tolerance as value ranging from 0 to 1. You should persist with the default 15 degrees’ value or 0 in some programs as it is the recommended option. If you want the surfaces to be smoother, you can go for higher values.

  • Always use CAD software for exporting STL files

    The next step to STL exporting is the use of specialized CAD software. However, the process of exporting might be unique in every software for 3D printing. That is why you must follow the specific method of exporting for a given CAD program.

    You can export STL file from different software by following below mentioned methods.

    • Solidworks

      Navigate to ‘Save As’ in ‘File’ menu. In ‘Set Save As’ box, select STL as the file type. Next, choose ‘Ok’ from ‘Options -> Resolution -> Fine (or Custom)’ menu.

    • 3DS Max

      Navigate to the 3DS Max Application Menu, choose ‘Export’ and then ‘Stereolitho (*.STL)’

    • AutoCAD

      Navigate to ‘Output -> Send Panel -> Export’. When the Command prompt appears, key in ‘Export’. After the ‘Export Data’ dialog box appears, key in a proper filename. Choose Lithography (*.stl) from ‘Files of Type’. Click Save. You can choose one or more than one solid objects.

    • Inventor

      Navigate to ‘File’ menu, choose ‘Print’ and then ‘3D Print Preview’. From top left of window, choose ‘Save Copy As’ and then ‘Save’

    • OnShape

      You would have ‘Part Name' here. Right click on it at bottom right. Choose ‘Export’ and from ‘Format’, choose ‘STL’. After specifying model units, choose export settings.

    • PTC Creo

      Navigate to ‘Save As..’ under File menu and then select ‘Save a Copy’. The Type is to be changed to ‘Stereolithography (*.stl)’. Once you click ‘OK’, a new ‘Export STL’ dialog box will show up. From under ‘Deviation Control’, change the export settings.

    • Rhino

      Navigate to ‘Save As’ under ‘File’ menu. Choose ‘Stereolithography [*.stl]’ from ‘Save As…Box’.

    • SketchUp

      Start SketchUp after downloading the version to STL or DXF plugin. From ‘Tools’ menu, choose ‘Export to DXF or STL’.

    • Solid Edge

      From File menu, choose ‘Save As..’. From ‘Set Save As..’, choose file type as STL. From ‘Options’, select ‘Export’ as option.

    • ZBrush

      You have to bring down the polygon count adequately by using ‘Decimation Master’. Choose ‘Export as STL’ from ‘3D Print Hub’ under ‘Zplugin’.

So, make the best use of this article if you wish to learn the best way to get your STL files ready for 3D printing. Besides, there are a few other things which you need to take care of when it comes to exporting for 3D printing. For example, you need to keep the chord height to 0.001 mm. Another good rule of thumb is to keep the angular tolerance to 15 degrees. Also, last, but not the least, make sure that you do not export CAD to STL if the file is larger in size. Following the above rules will help you to achieve optimal results, be it for printing of 3D jewelry files, mechanical components, or healthcare equipment. However, if it is still confusing, then opt for a service provider that can do the task for you. Thankfully, you will find a lot of companies that offer services for the same.

Special Rules for the STL File Format

Here are some special rules that apply to the STL file format, which you should know about:

  • The Vertex Rule

    According to this rule, every triangle should share two vertices with the adjacent triangles. This rule should be followed during the tessellation of a 3D object’s surface.

  • The Orientation Rule

    This rule suggests that the orientation of a 3D object’s facet should get defined in two ways. The first rule states that the normal should point to the outer side. According to the second rule, which is also referred to as the right-hand rule, the vertices get listed in the counterclockwise direction. This rule guarantees data consistency.

  • The All Positive Octant Rule

    This rule states that the coordinates of the vertices of the triangles should all be positive. This translates into the fact that the 3D object would remain in the 3D Cartesian System’s all-positive octant. The rule is meant to save space; if 3D objects are made to remain at any place in the coordinate space, professionals would have to deal with negative coordinates.

  • The Triangle Sorting Rule

    According to this rule, the triangles need to appear in the rising z-value order. This rule facilitates faster slicing of 3D models.

How to Optimize STL Files

The STL file format replicates a CAD model’s surface to some extent using triangles. However, this is never perfect and the facets give the model a degree of coarseness. A 3D object having the same degree of coarseness as the STL file would get generated. However, if you go on decreasing the size of the triangles, you can improve the approximation and the print-quality at the same time. When you decrease the triangle-size, you would need more triangles to cover the entire surface. This would create massive STL files that most slicer would fail to process. Such huge files would also be difficult for you to upload. So you should know how to strike a proper balance between print-quality and file size. In some CAD software, you would come across certain settings while getting your STL files exported. Such settings determine the facet-size, file-size, and even the print-quality.

STL File Alternatives

Notably, the STL format is not the only 3D print-ready format; more than 30 3D printing file formats have been invented. OBJ is a widely-used file format, which can keep texture and color profiles saved. The Polygon (PLY) is another format that is used to save scanned 3D objects. Off late, The 3MF Consortium is looking to introduce a new file format called the 3MF format. It is expected that this file format would make the 3D printing process more efficient.

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