Exporting to STL for 3D printing

Note: This shows how to export files to STL format, which is the required format for using our pricing calculator. If you want to print in color, please attach a .WRL (multicolor/textured parts), or a .OBJ .3DS, .STP if requested by the printer.


The CAD to STL Process: CAD to STL

After designing a model in a CAD program, you save the design as an STL file. (Most CAD programs have this function.) An STL file renders surfaces in the CAD design as a mesh of triangles. The number and size of the triangles determine how accurately curved surfaces are printed. You control the number and size of the triangles by setting the following parameters when you create the STL file from the CAD design:

Chordal Tolerance / Deviation

The maximum distance between the surface of the original design and the tessellated surface of the STL triangle.

Angle Control

The angular deviation allowed between adjacent triangles. This setting enables you to increase tessellation, necessary for surfaces with small radii. (The smaller the radii, the more triangles are needed).

STL File Format

You usually have the option to save STL files in either binary or ASCII format. Binary files are smaller (by a factor of 6!), so this format is usually preferred. However, ASCII files can be visually read and checked.

STL Geometry Check

Model designs containing holes and gaps adversely affect the quality of the printed model. Therefore, you should perform a geometry check of the STL files before continuing. Thirdparty software for this purpose attempts to fix the geometry of problematic files. 

Software Export to STL

AutoDesk Inventor
  1. Go to the File menu, then select the ‘Save Copy As’ option
  2. Select STL from the Types drop-down
  3. Click the Options button, and choose the High detail level
  4. Click the Save Button
Autodesk Inventor allows you to save both individual parts and assemblies in STL format, at all design levels.
Phase 1: Saving a model design in STL format
To save an Autodesk Inventor model design as an STL file:
  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… > To Save copy as dialoge box opens
  3. In the Save as type field, select STL Files (*.stl), and click Options. The STLOut Save Options dialog box opens.
  4. Select High and click OK.
  5. In the Save Copy As dialog box, click Save.
  6. Note: To change the values associated with each of the resolution settings (High/Medium/Low) you need to edit the Windows registry.
Catia
  1. Select STL command
  2. Maximum Seg to 0.015mm
  3. Select the model and > select Yes
  4. Select Export > type File name > OK
Catia can import almost any design-file format, but only those that include solid data (IGES, STEP, Parasolid, etc.)

STL files can be saved – with a special add-on module. Catia V5 is capable of creating STL files from parts (CatiaPART files), but not from assemblies (CatiaPRODUCT files) or geometrical representations (car files). 

Therefore, source files, including those saved in a neutral format (STEP or IGES, for example), must be saved as parts. If the source design was saved as an assembly, it is imported to Catia as a product.

To create an STL file from it, you must first convert it to a multi-bodied part. The procedure described below is one of several methods for doing this.
 Phase 1: Saving a model design in STL format
Opening and Preparing the Source File:
  1. From the File menu, select Open, and open the source file. If the source design was saved as an assembly, it is imported as a CatiaPRODUCT model.
  2. Save the product file.
  3. From the File menu, select New > Part, and give it the name of one of the components.
  4. In the product window, select this component, and copy it (with the Edit menu or the right-click pop-up menu).
  5. In the part window, paste the component.
  6. Repeat steps and until you have copied all of the components and pasted them as individual parts. Figure on the right shows the result of pasting the components of the product into individual part files.
  7. From the File menu, select New > Part, and give it a name suitable for the combined model.
  8. Copy each of the individual components (parts) from the working files and paste them into the new (combined) model file.
Since the geometries of all of the parts are retained, they should be aligned correctly in the combined part. The new part is now ready to be exported as an STL file.

Phase 2: Re-aligning parts (if necessary)
Occasionally, because of the way the original assembly was designed, some of the components may not align correctly in the combined part. If so, you must align them, using the Constraints feature, from the Insert menu.

Before saving the file, it is advisable to review the settings that determine the accuracy of the model – and the size of the file. To see these parameters:
  1. From the Tools menu, select Options.
  2. In the Options dialog box, display the Performance tab.
  3. Under the General category (on the left), select Display.
  4. Pay attention to the 3D Accuracy settings.
Fixed – The lower the setting, the finer the details of the model in the STL file. A very small setting results in a very large STL file. Curves’ accuracy ratio – The higher the setting, the smoother the surface will be, when dealing with complex geometries, especially if surfaces contain sudden small changes with small radii (like the bumps on a golf ball).

Phase 3: Saving the Part as an STL File
After preparing the part, as described above, proceed as follows:
  1. From the File menu, select Save As.
  2. In the Save As dialog box, select stl from the Save as type pull-down list.
  3. Click Save.
Since Catia5 supports non-continuous model designs, importing geometry into a part by copying and pasting is not problematic.
Google Sketchup  Ensure model is closed (watertight) and has thickness Convert to .STL using a supported plugin

IronCAD
  1. Right Click on the part
  2. Part properties > Rendering
  3. Set Facet Surface smoothing to 150
  4. File > Export
  5. Choose .STL
With IronCAD, you can only save parts as STL files.
 When working in assembly mode, you must save its component parts as individual STL files. The procedures for doing so are described below.

Saving a model design in STL format
  1. Open the model design in IronCAD.
  2. Right-click on the part and, from the pop-up menu, select Part Properties… The Part dialog box appears.
  3. Make sure that the Rendering tab is displayed.
  4. Change the Surface Smoothness setting to an appropriate value for your model.
  5. If you have not established an appropriate value, try 150. The higher the number, the smoother the model surface will be.
  6. Change the Max edge length setting to an appropriate value for your model. If you have not established an appropriate value, try 0.05. This setting produces good results, but increases file size and may require several minutes to render the model to STL format.
  7. To create smoother model surfaces, when designing spherical and torus geometries, select the Triangulated mesh check box. Selecting this check box results in larger STL files, but may produce smoother curves in models. If the surfaces of the model design are planes, this setting does not improve the results.
  8. Click OK to save the settings and close the dialog box.
  9. From the File menu, select Export > STL.
  10. In the Stereolithography dialog box, make sure PC is selected, and select the Binary output check box.
  11. Click OK to save the settings and create the STL file.
McNeel 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. Max Angle = 20, Max aspect ration = 6, Min edge Length = 0.0001
  7. OK

McNeel Rhino - version 3 and later
Rhino enables extensive control of STL properties when saving designs as STL files.

Because Rhino software is surface-based, the complete model design (even if an assembly) is saved as a single STL part.

Saving a model design in STL format
  1. Open the model design in Rhino.
  2. From the File menu, select Save As. The Save dialog box opens.
  3. In the File name box, enter a name for the new STL file.
  4. In the Save as type box, select Stereolithography [*.stl].
  5. Click Save.
  6. In the STL Mesh Export Options dialog box, set the STL tolerance – the maximum distance allowed between the surface of the design and the polygon mesh of the STL file. In the Polygon Mesh Detailed Options dialog box, set the STL tolerance in the field labeled Maximum distance, edge to surface, as shown in the figure. 
  7. If you do not know the other settings appropriate for your model design, try these: a) Maximum angle – clear, b) Maximum aspect ratio – clear, c) Maximum distance edge to surface (Tolerance) – less than half of the printer’s resolution. For example, the setting shown in the figures above (0.01 mm) is a good setting for printing models at a resolution of 30 ?m (0.03 mm).
  8. Click OK.
  9. In the STL Export Options dialog box, set the file type as Binary and click OK.
If the Export open objects check box is selected, STL files will be created for each of the objects currently open. If this check box is cleared, an STL file is created for the selected object.

Important: STL files are suitable for 3D printing if the models they describe are "watertight" - that is, they do not contain holes or gaps. If the following message appears, click Cancel and fixd the model design (see image FIgure 30) before saving it as an STL file.
 Troubleshooting Model Designs
If a model design contains holes or gaps, it is not suitable for 3D printing. Before saving it as an STL file, you must make it “watertight.”

To close holes and gaps in a model design:
  1. Select the entire object.
  2. From the Edit menu, select Join. or – Click the Join icon on the side toolbar. This command reduces the number of surfaces and fits them together tightly. (The entities are not fused together into one unit.) The message in the command bar indicates this.
  3. Select the object. You can select the entire object, but to save time, you may select only the problematic entity.
  4. From the Tools menu, select Polygon Mesh > From NURBS Object. or – Click the Mesh from Surface/Polysurface icon on the side toolbar. The Polygon Mesh Options dialog box opens.
  5. Click Detailed Controls… The Polygon Mesh Detailed Options dialog box opens.
  6. Enter the same settings as before and click OK.
  7. Select the entire object.
  8. From the Tools menu, select Polygon Mesh > Weld.
  9. In the command bar, type 180 for the angle tolerance, and press Enter. With an angle tolerance of 180, the Weld command always merges adjacent triangle points.
  10. From the Tools menu, select Polygon Mesh > Unify Normals. This setting unifies the normals of all triangles, so that they have the same definition for “up.”
  11. To validate that the object is watertight, type SelNakedMeshEdgePt in the command bar, and press Enter. If the resulting object contains holes or gaps, the mesh point is highlighted in the display.
  12. Repeat the Save As procedure
Pro/Engineer 
  1. File > Export > Model
  2. STL
  3. Set chord height to 0. The field will be replaced by minimum acceptable value.
  4. Set Angle Control to 1
  5. OK
Pro/E allows you to save model designs in STL format.

This is done at all levels of design, for both individual parts and assemblies. When dealing with assemblies, you can specify parts of an assembly to either include or exclude from the resulting STL file. Use the procedure below for saving both parts and assemblies as STL files for printing with 3D printers.
To save a Pro/E as an STL file:
1. Check that the model design is continuous and “watertight.” This step is especially important if the design was imported from a neutral design format. Non-continuous bodies are likely to result in defective models. You cannot always check for continuity by examining the model displayed in shaded view. Therefore, use the following method:
  • View the model with hidden lines displayed.
  • From the View menu, select Display Setting > Scheme > PreWildfire. The model surfaces are displayed in magenta. If the design is continuous, the contour lines are white. If there are gaps, the lines are yellow.
  • Fix the model design, if necessary, before saving it as an STL file.
2. From the File menu, select Save a Copy. The Save a Copy dialog box appears.
3. From the Type pull-down menu, select STL.

Deviation Control
The Deviation Control settings in the Export STL dialog box affect the accuracy of the model and the size of its file. Chord Height – Also known as “chordal tolerance,” this setting specifies the maximum distance between the surface of the original design and the tessellated surface of the STL triangle (the chord). Therefore, the chord height controls the degree of tessellation of the model surface. The smaller the chord height, the less deviation from the actual part surface (but the bigger the file).

Angle Control
This setting regulates how much additional tessellation occurs along surfaces with small radii. The smaller the radii, the more triangles are used. The setting can be between 0 and 1. Unless a higher setting is necessary, to achieve smoother surfaces, 0 is recommended.

4. When you have made all of the required settings, click Apply and OK to create the STL file.

Saving a Pro/E Assembly as an STL File
1. From the File menu, select Save a Copy. The Save a Copy dialog box appears.

2. From the Type pull-down menu, select STL. The Export STL dialog box appears. In addition to the settings used when exporting a part STL, this dialog box enables you to specify the parts of an assembly to either include or exclude from the resulting STL file. In the dialog box one of the parts of the assembly (the tire) has been excluded, leaving two parts (the hub and the main wheel) to be exported to the STL file. The design resulting from these settings (when you click OK) is shown on the left.

3. When you have made all of the required settings, click Apply and OK to create the STL file.
 Solid Edge
  1. Open Model & select File > Save As
  2. Select File type as STL
  3. Options > conversion tolerance to 0.015 mm
  4. Surface Plane Angle > 45°
  5. Select Binary type and OK
  6. Name & Save STL file
 Solid Edge - version 16 and later
Solid Edge software from Siemens PLM (formerly USG) supports STL output at the core level, enabling you to save both parts and assemblies as STL files. Note, however, that when saving an assembly, all of its components are included in a single STL file.1

Phase 1: Saving a model design in STL format
  1. From the File menu, click Save As. The Save As dialog box opens.
  2. From the Save as type drop-down menu, select STL documents (*.stl) and click Options... The STL Export Options dialog box opens.
  3. Set Conversation tolerance and Surface plane angle to appropriate values for your model. The lower the Conversation tolerance, the finer the tessellation. The lower the Surface plane angle, the greater the accuracy (noticeable in small details). As a rule, the finer the tessellation and the greater the accuracy, the larger the size of the STL file, and the longer it takes to generate it.
  4. In the Output file as section, select Binary. Binary STL files are much smaller than STL files saved in ASCII format.
  5. Click OK.
  6. In the Save As dialog box, click Save.
Solid Edge is technically capable of creating individual STL files from the components of an assembly, but this functionality is not built into the program. It is achieved through the application programming interface (API), using Visual Basic scripts. This solution does not enable a visual preview of the polygon mesh before saving the STL files.
 SolidWorks
  1. File > Save As
  2. Set Save As Type to STL
  3. Options > Fine > OK
  4. Save
  5. STL settings: How to change STL settings
  6. File > Save As
  7. STL > Options
  8. For a smoother STL file, change the Resolution to Custom
  9. Change the deviation to 0.0005in (0.01 mm)
  10. Change the angle to 5 (Smaller deviations and angles will produce a smoother file, but the file size will get larger)
 SolidWorks 2000 and later
Saving a model design in STL format
SolidWorks allows you to save model designs in STL format, at all levels of design, for both individual parts and assemblies, including the ability to save a multi-bodied model as a single STL. To save a model or a model assembly in STL Format:
  1. From the File menu, select Save as. The Save As dialog box opens.
  2. From the Save as type drop-down menu, select STL (*.stl).
  3. Click Options... The Export Options dialog box appears, and the model is displayed in tessellated view. STL is the File Format selection.
  4. In the Export Options dialog box, in the “Output as” section, select Binary. (The resulting file size will be much smaller than a file saved in ASCII format.)
  5. In the “Resolution” section, select the appropriate option. If you select Custom, you can manually adjust the Deviation and Angle settings, as needed. These settings affect the tessellation of non-planar surfaces, as follows: a) Lower Deviation settings result in finer tessellation. b) Lower Angle settings result in with greater accuracy, noticeable in small details. c) As a rule, the higher the resolution, the larger the size of the file, and the longer it takes to generate.
  6. For Single Material Builds Make sure that the following check box is selected: Save all components of an assembly in a single file. This ensures that all components are saved as a single STL file.
  7. For Dual Material Builds Make sure that the following check box is NOT selected: Save all components of an assembly in a single file. This ensures that all components are saved as separate STL files.
  8. Click OK.
  9. In the Save As dialog box, click Save.
  10. In the confirmation message, click Yes.
 UGS NX UGS NX
  1. File > Export > Rapid Prototyping
  2. Output type : Binary
  3. Triangle & Adjacency Tolerance: 0.015 mm
  4. Set Auto normal Gen to ON
  5. Set Normal Display to ON
  6. Set Triangle Display to ON
  7. File Header Information: Press OK
  8. In case a error messages "Negative coordinates found" appears, it can be ignored
UGS NX - version 4 and later
NX software from Siemens PLM (formerly USG), supports STL output at the core level, enabling you to save not only entire parts as STL files, but also selected surfaces of a part.

This gives you great flexibility when preparing objects for 3-D printing. In addition, assembly output enables you to save several components as a single unit while maintaining each component as a separate volume (shell).

Saving a model design in STL format
  1. From the File menu, select Export > STL… The Rapid Prototyping dialog box opens.
  2. Set Output Type to Binary. Binary STL files are much smaller than STL files saved in ASCII format.
  3. Adjust the Triangle Tol setting to an appropriate value for your model. This is the maximum distance allowed between the surface of the original design and the tessellated surface of the STL triangle, and affects the smoothness of the model surface.
  4. Adjust the Adjacency Tol setting. This determines if two adjacent surfaces “attach”. If the distance between the two surfaces is less than this setting, they are considered attached. This setting must be less than the printing resolution. For example, when printing models at a resolution of 30 micrometers (microns), the setting must be no more than 0.03.
  5. Click OK.
  6. In the Export Rapid Prototyping dialog box, enter file name and click OK.

See more information at: http://www.stratasys.com/customer-support/cad-to-stl/autodesk-inventor