We recently wrote an overview on How to Prepare CAD Files for 3D Printing, going over some general considerations and steps to properly export your 3D printing files.
There are some unique considerations to keep in mind when preparing 3D print files specifically in Rhino, so for this post, we're going to go into more detail on how to export your CAD models here.
Let’s dive in!
Set correct tolerances before you start modelling by finding the tolerance of the program you are exporting your model to and setting Rhino tolerance to be 10 times that (i.e. printer tolerance is 0.1mm, so Rhino tolerance should be set to 0.01mm).
Rhino file tolerance can be set from the document properties window, units tab.
No matter what units you use to create your model, files exported from Rhino are almost always read as mm. Make sure your units are set to mm before exporting your file for printing.
For successful 3D prints, the 3D model should be watertight, i.e. if you dropped the model in a bath, no water would leak inside.
To achieve a watertight model, you need a closed polysurface. The most common reason models become unprintable is due to bad objects and naked edges.
Bad Object: Objects that violate NURBS rules or have structural problems. They often appear after joining and Boolean operationsNaked Edge: Surface edges not connected to other surface edges, which create open meshes that cannot be 3D printed
Find open polysurfaces by selecting Analyse Direction → Show Edges → Select Open Polysurfaces and then follow the steps below:
Rhino creates a NURBS solid model. However for 3D printing, the model must be exported as a mesh model. To achieve this, follow these steps:
Even with the recommended settings, your STL mesh may have errors which makes it unsuitable for 3D printing. Here are the most common problems and solutions:
If your mesh polygon number is higher than 1,000,000, the file will be unwieldy and difficult to print. Small items like jewelry should have around 150,000 polygons, while a 30 x 30 x 70mm object will have more like 600,000. Use the Reduce Mesh command to make your file more manageable.
The ‘positive’ direction of your mesh faces may not be coherent throughout the model. Use the ‘Unify Mesh Normals’ tool to fix the issue.
Selecting open meshes and performing a naked edge analysis as described above will identify any holes in your mesh. This is easy to fix using the ‘FillHole’ command.
Can be caused when multiple mesh surfaces share a vertex or edge. Use the ShowEdgestool as before to find these errors. It’s recommended to view the object in wireframe mode for easier analysis; frequently the excess faces are inside the model. Use the ‘Delete Mesh Faces’ tool to remove the excess faces.
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