Manage and export valid 3D files for 3D printing from Rhinoceros
2.1. 3D model analysis
The simplest way to identify an open
When an object is made of an open
If the model stays closed, you will see “No objects added to selection” in the command line.
By doing this, you can find out which object is made of an open
Once you have the isolated object you can proceed to do the naked edges detection.
Edge analysis for naked edges
The edge analysis tool will help you detect where and if a
This command will light up the open contour according to the selection color in the edge analysis box.
The “select bad objects”
To have more detailed information about a bad object, you can run a diagnostic using “Check objects” available in the main menu under ‘Check objects’. A popup window will give you more information about the model e.g. if there is any bad geometry or “Rhino
You can select the model and go to properties in the right column to select
2.2. Fix NURBS 3D model
Repair naked edges
After finding the naked edges, you can fix them with a join
However, sometimes there are missing surfaces. In this case, the best method to solve the problem is to create a new surface that will be in perfect contact with the surrounding surfaces edges; use join to create a closed
When the surface edges are more distant to each other than what your Rhino file tolerance allows -for example when 2 surface edges are 0.1 mm apart and Rhino tolerance is 0.001- the join command won't work. This type of naked edge can be fixed by using a forced union. If precision 3D modeling is not important for the 3D modeling work, this could be a quick fix operation. It allows Rhino to join the edges without taking the minimal tolerance into account.
You can find the forced union tool under ‘Surface menu/ Edge Tools/ Join 2 naked edges’ or by typing “JoingEdge” into the command line.
This is a quick solution, not the best one, but it is better to have a clean closed
Fixing bad geometry
As was mentioned in the valid objects section, bad geometry is mostly generated from bad surfaces due to an error that occurs during the adjusting of the trim curve.
Usually, bad surfaces are fixed by making the model explode and then rejoining it. If this does not fix the model, it is because there are complicated NURBs problems in the structure. You can try to fix them with the following tool operations:
- First of all, identify the bad surfaces and hide everything else temporarily. You can separate the bad surfaces from the
polysurfaceusing “Bad Surfaces Extract” by typing “ExtractBadSrf” in the command line .
- Once you have the bad surfaces isolated, proceed to restore the edges of the surfaces to their original state before they were joined - with the command “Rebuild Edges”. You can find this in the main menu ‘Fillet Surface/ Rebuild Edges’ or typing in the command bar “RebuildEdges”. This operation will detach the surfaces so you can rejoin them again. In some cases, this might work. After this operation, you should check if the surfaces are repaired or if there are at least some of them fixed.
- If the surfaces were not completely fixed, you can select a bad surface and remove the trimming boundary from a surface using the command “Untrim” followed by “keep trim objects”. This is available in the main menu ‘Fillet surface/ Untrim’ or typing in the command bar “
Untrim”. Select the trim curve and trim itagain. Then check if the surface is no longer a bad surface. You should apply the same operation to the other bad surfaces. For the last part,try to unhide everything and make them all join up again. Check for bad geometry with “Check objects ” .If this does not work, it is usually because the join operation is trying to force things together that do not fit correctly. If so, it is recommended to find the bad surfaces and analysethe union with the contiguous surfaces.
Multiple solids model
As explained before, in the “proper 3D
2.3. Create and export a mesh
As Rhino use a
For obtaining optimal results, it is recommended to have a better understanding and control of the mesh creation settings before you start exporting. You can create a mesh without exporting the solid by using the command “Mesh” - located in the main left command bar - or by typing in the command line “Mesh”. Right away a popup window will show with the “Polygon Mesh Options” along with some simple controls. In order to have more control over the
Tolerance for mesh creation
A mesh is composed of many faces that actually make up your model. The quantity of the faces depends on the mesh density. A model with few faces will look faceted or it will have a low polygon appearance. A model with many faces will look smooth and have a high polygon appearance. The more faces, the smoother your model will look but be careful because an exaggerated number of polygons could turn your 3D model in an oversized file, making it more difficult to handle.
A good 3D print mesh looks nearly black. The polygons distribution is organized and balanced within the model. A good example is the high polygon picture displayed above.
The recommended values in a general way to set up the tolerance for small objects for 3D printing are the following.
- Density: 0.0
- Maximum angle: 0.0
- Maximum aspect ratio: 0.0
- Minimum edge length: 0.0
- Maximum edge length: 0.0
Maximum distance edge to
surface: “The same as the tolerance file” (tolerance settings)
- Maximum edge length: 0.0
- Minimum initial grid quads: “Variable depending on how the mesh looks”
The minimum initial grid is a variable value depending on your model. This number will help us to define the number of quadrangles per surface in the initial mesh grid. Namely, the polygons quantity on each surface. Bigger values result in slower meshing, more accurate meshes and a higher polygon count with more evenly distributed polygons. For example a minimum initial
After the mesh
For example, in the model displayed below there is mesh with
2.4. Correct mesh for 3D printing
Closed and compact mesh
The mesh object must be compact meaning no vertices, edges or faces around the main model. All the pieces that make up the model should have a volume, there can't be faces without any mass.
A 3D printable mesh is a correctly manifolded mesh. The term manifold defines a mesh in which all its triangular edges are directly and individually connected to one another creating a closed volume.
Non-manifold errors are generally produced by the following reasons:
- Several faces share one edge
- Several faces share the same point or vertex
- There are some unnecessary faces intersecting the main body of the model or at the interior of the model
Coherent mesh orientation
The faces that compose the mesh may not have the same normal orientation. That means that while one face
One single shell
Every part that makes up your digital model needs to be made out of just one shell. When you select a single part of your model, you usually should see in the command line “1 mesh added to selection” this
2.5 Mesh analysis
The mesh analysis tools could be really helpful to check - your already exported STL from Rhino - if you want to confirm that everything is right with it or if you have a model that needs to be checked and repaired.
Open mesh detection
The detection of an open mesh can be done with the command “select open meshes
If the model is closed you will see “No objects added to selection” in the command line. This process lets you find out which meshes are open. Once you have the isolated the object, you can proceed to do the naked edges or
Non manifold edges analysis
The edges analysis tool will help you to find out if there are
You can fiind the tool that will help you in the main menu bar mentioning ''Analyse Direction/ Show edges''. This will make a new small box pop up where you choose the object to be
It is recommended to use the tool with the volume displayed in
Mesh orientation analysis
It is easier to identify the faces (with a normal direction) that present a problem if after running a naked edges test - you can still see a hole in a shaded display mode when your mesh is completely closed and there are no naked edges. This means that the face that
Another way you can see more on the normals
You can check if your final mesh is a 3D printable mesh by running a diagnostic check using the “Check objects” tool that is available under the main menu. A popup window will give you more information about the model if there is any problem with it - or it will say “This is a good mesh”. You can read the description and see if there are no more errors that were mentioned before.