Additive Manufacturing or 3D printing is based on the concept of adding material during the production process to produce a physical object from a digital 3d model.  There are a wide range of Additive Manufacturing techniques, although the manufacturing process might differ as well as the materials used, the principle is similar and is based on adding/curing material layer by layer to produce the desired part. 

The process to make a 3d print starts with creating/finding a digital 3d model of the object you want to print. This model will then be imported in slicing-software which can translate the 3d geometry information into machine code. The 3d printer will use this code to 3d print the object. 

 To make a 3d print we need a digital 3d model. There are several methods of creating/finding 3d geometry which can be 3d printed. 

• Model the 3d geometry in one of the many 3d modelling software’s available: Most 3d software will have an option of exporting a file format which the slicing software can read. The file format used by slicing software is generally .stl. Other formats might be supported based on slicing software used. 
• Photogrammetry: Photogrammetry lets you generate a 3d model from a series of photos of a physical object. It is a form of 3d scanning that doesn’t need an expensive 3d scanner. The camera of a mobile phone is sufficient. The results can be quite impressive. The software you need to convert the images into 3d geometry can be found on the internet. It is often free software.  The models can sometimes be problematic to print, however the Shrinkwrap option in Rhino can be used to generate a 3d printable 3d object of the scanned 3d object.
• Download a 3d model:  There are a wide range of websites where you can download 3d printable models for free like Thingiverse and MakerWorld. These models are especially made for 3d printing and should be 3d printable without too much trouble. 
• AI: Yes, also in the field of 3d modelling AI makes it mark. The development in this field is impressive. New options of generating 3d geometry with the help of AI are coming available. 

In this guide you will go through all the steps needed to export a correct STL mesh model that can later be sliced in a slicer software for later 3D printing. Because there are various sources of 3D geometry for 3D printing as mentioned above, the quality of the 3d model can vary quite a lot. Much of the time spend on creating a 3D print is in the preparation of the 3D file so it can correctly be sliced.  

For the modelling of 3D geometry, we will refer you to the Rhino modelling course material on the Digipedia. 

The geometry the Slicer software uses is a Polygon. This a relatively simple description of 3d geometry. The shape is defined by a set of coordinate points called vertices. Between 3 vertices a triangle is defined, called a face, or between 4 vertices called a quad.  This is the visible surface of the geometry. The edges of these faces and quads are called not surprisingly Edges. Because not all 3d modelling is done with Polygons and other geometry descriptions are used like Solids, PolySurfaces and SubD’s the produced 3d geometry has to be converted to a Polygon to make it 3D printable.  Misstakes in the conversion process might lead to the need of repairing the resulting 3D polygon geometry.

You will learn:

• Basics of watertight geometry
• Concept of how a 3D printer operates
• How to prepare your 3D model in Rhino
• Export the file as STL

Models for 3D Printing 1/2

Prepare the 3D Model in Rhino (or other CAD software)link copied

1. Proper Units and Scale

The foundation of a successful 3D print lies in a well-prepared 3D model. Rhinoceros is a fantastic tool for this, but attention to detail is crucial.

• When you create a new file in Rhino, it will ask which kind of scale you want to use.

Select the Small Objects – Millimetres option.

• If you already have a file, check your units in Rhino before you start further constructing or importing 3dmodels into Rhino. You can check the units in the bottom left corner of the interface. If they are not correct you have to set them to millimetres 

• Set your units correctly. In Rhino, go to Tools > Options > Document Properties > Units. We recommend working in millimetres (mm) as this is the standard unit for most 3D printers and slicers. Align the model with the printer’s coordinate system, note the size of the model according to the printer you are going to use. Max build size for Bambu X1C: 256  256 × 256 mm, while Kobra 2 Max: 420 × 420 × 500mm). 
• Always model at a 1:1 scale. It is better to model in the right final size within Rhino from the start. This prevents possible scaling errors and ensures accurate dimensions. 

2. Watertight Solids (Manifold Geometry)

• Your model MUST be a “watertight” volume. This means it has no open edges, no internal self-intersecting faces, and no duplicate surfaces. Think of it like a perfectly sealed container – if you poured water into it, it wouldn’t leak. If the object is not completely closed the software will have problems determining what is inside and what is outside. This can lead to slicing problems.  
• You can check this in the property’s menu of your geometry. 

• Common issues and how to fix them: 
  • Open Edges: Use ShowEdges > Naked Edges to identify unjoined edges. Use commands like Join, CloseSrf, Cap (for planar holes), or manually create and join surfaces to close gaps. 

You can double-check your model with ShowEdges > All Edges and ensure no  naked edges are visible. For complex models, the Analyze > Diagnostic > Check     command can also be helpful. 

• • Non-Manifold Edges: These are edges shared by more than two faces. Use SelNonManifold to find them. Often, exploding and rejoining or recreating problematic areas can help. 
  • Self-Intersecting Geometry: This occurs when parts of your model pass through themselves. Use Intersect to check for this. Boolean operations (BooleanUnion, BooleanDifference) are common culprits if not used carefully. 
  • Duplicate Surfaces/Objects: Use SelDup to find and delete any overlapping or identical geometry. 

• If nothing works, no problem, Rhino has a new option especially for making even mediocre geometries printable. This option, Shrinkwrap, will create a new surface enveloping your 3d model.  
  It generates a literal Shrinkwrap of your geometry. If nothing else works this is the go to  command.  Type the command Shrinkwrap in the command line and select your object. 
  The settings allow for the accuracy of the envelopment. The smaller the Target Edge length  the more accurate the Shrinkwrap will be and the more computational power it will need to produce the Shrinkwrap.  

3. Saving your model as an STL file

• Saving Your Model as STL: 
• Export as STL: Once your model is ready, be it mesh or NURBS, select all the geometry you want to print and go to File > Export Selected… or File > Save As… and choose “Stereolithography (*.stl)” as the file type. 
• STL Export Options: 
  • Binary (recommended): This creates smaller file sizes. 
  • Tolerance: This setting determines how accurately the curved surfaces of your model are tessellated into triangles. A lower number (e.g., 0.01mm – 0.05mm) will result in a finer mesh and a more accurate print, but a larger file size.  Too high a number will make curved surfaces appear faceted. 

Models for 3D Printing 2/2

Additional Tipslink copied

Additional tips for model preparation and understanding different printers’ settings. 

• Minimum Wall Thickness: Too thin walls can still lead to print failures or fragile parts. As a general rule, aim for a minimum wall thickness of at least 1.5mm to 2mm for structural integrity. For decorative features, you might go slightly thinner but always test the settings. Be aware the printers of the printfarm have a 0.8mm or 1.0mm nozzles and therefore are less accurate than the printers with a 0.4mm nozzle. Similar to the difference between drawing with a sharp pencil or a marker.  
• Consistent Thickness: Try to maintain a relatively consistent wall thickness throughout your model where possible. 
• Optimize Level of Detail for Printing: While Rhino handles complex NURBS surfaces, excessive detail in small features (e.g., extremely fine guardrails, tiny text) might not translate well to FDM printing or might significantly increase print time without visual benefit. 
• Consider Simplification: If your model is overly complex with tiny features, consider simplifying them for printing purposes. Small changes can drastically reduce print time / material cost. 
• Known problematic geometry: Geometry from Grasshopper can be so complex that repairing is not an option. In that case use the Shrinkwrap option.  Less problematic but still can require some repair is the geometry imported from Sketchup.  
• You can already position your model strategically for printing within Rhino before exporting, to save yourself some time on rotating it inside Bambu Studio later