Digital Fabrication

3D Printing

How to prepare files for 3D print. Option A

Rhinoceros 4.0

Since most people will be generating their models from within Rhino, this guide will show instructions specifically tailored to it. These steps are analogous in any other modeling application, though the specific commands may differ.

Analyze your model

Analyzing your model is the most important step to making sure that your print comes out successfully. There are 4 basic things that you need to check to make sure that the object is ready for meshing, and instructions below will show you how to do this:

1. object is valid AND closed (i.e. airtight) ***NO NAKED EDGES*** 2. object contains no BAD surfaces and/or objects 3. object DOES NOT intersect itself 4. object surface normals are consistent.

- 1. valid & closed

to check that the intended object is valid and closed, in Rhino select the object

Edit menu: Object Properties

Or on the standard toolbar, click Object Properties

select ‘Details…’

Make sure the dialog says “Valid polysurface” AND “Closed solid polysurface…” in the text if your object is NOT a ‘closed solid polysurface’, you need to close it. The first thing you need to do is find where there is an opening. If it is not obvious, you can try using the ‘show naked edges tool’

Analyze menu: Edge Tools > Show edges

Select the Naked Edges box

This now highlights the free edges in your model. These need to be sealed up using any number of normal modeling methods before you can continue

- 2. bad objects

Rhino is a NURBS modeler, and sometimes geometry is created that does not obey NURBS rules, and causes errors. There is an off chance that your model has a bad object in it.

Analyze: Diagnostics > Select bad objects

if a bad object is selected, then simply delete it. Otherwise continue on.

- 3. self-intersecting solid

Make sure your object does not have geometry that intersects itself. This will jeopardize a successful print. You will need to rebuild your model such that it does not do so.

- 4. Surface Normals

Select your object. Select Analyze > Direction from the menu and confirm that all surface normals are oriented in the same direction.

Create a mesh of your model – and check it

Rhino generates a mesh in order to export the file to the .STL format. There are factors that you will want to specify based on the geometry of your part in order to ensure that your 3D print comes out looking acceptable.

Tools menu: Polygon Mesh > From NURBS Object

Select the objects

Go to ‘Detailed controls…’

make sure your dialog box resembles the one shown here.

n. b. these values are for millimeter-based models, the ‘maximum edge to surface box’ should reflect the units and scale of your object. It defines the accuracy of the mesh. A value of zero in any box disables the function.

This procedure is automatically invoked when you go to export your model, but if you are unfamiliar with this process or wish to exercise greater control over the mesh generation, you will want to do this as a separate step.

check it

right-click on the viewport name and make sure you are in shaded view

right-click the viewport name again and select flat shade. This will visualize what the mesh looks like, and it will be a good indicator to what your final printed part will look like. If the mesh is too jagged, simple delete the mesh and re-mesh the original model with a higher tolerance.

export your model

select the mesh you have just created (not the original polysurface!)

File menu: Save as > Save as type:

Select ‘Stereolithography (*.stl)’ format

Make sure to specify a Binary file format in the STL Export Options dialog box. To confirm a good model: import the .stl file back into rhino, and analyze it in a similar fashion as outlined above. The CheckMesh help file in Rhino is extremely useful in troubleshooting bad meshes.

How to prepare files for 3D print. Option B

Models are created in 3D programs such as Rhino and must be saved in STL format. Use the following steps to prepare your model in Rhino 4.0.
When working with surfaces, use BooleanUnion to combine the objects into one polysurface. Click Solid > Union.
After the Union command has been applied, create a Polygon Mesh. Highlight the object, select Mesh > From NURBS Object. With highly curved surfaces, increase the number of triangles in the mesh. Straight surfaces need less.
Next, click the object to select the Polygon Mesh.
Issue the command CheckMesh to see if you have a good mesh. If you have a bad mesh, search the Rhino help for 'check/repair meshes' . This will give you many fix-it commands. A common problem is naked or unjoined edges, which can be revealed with the command ShowEdges, and usually fixed with the MatchMeshEdge command. FillMeshHoles will repair holes, but is more likely to change the shape of the model. ExtractDuplicateMeshFaces will separate identical faces for easier removal, but be aware it could generate naked edges. It may be helpful to make a copy of the mesh before using these tools in order to check the results. Visit this page for more tips on creating a good stl file from Rhino.
When done fixing the model, export the Polygon Mesh as an STL file. Select the mesh, then click File > Export Selected. Change the Save As Type to STL. When the File Type Options appears, choose BINARY.