Mesh Manipulation with Blender

Blender is a useful alternative to Rhino for working with meshes: rebuilding meshes (decimate geometry), splitting models, filling holes and to smoothing (auto shade) meshes.

2.0 Useful Resources

2.1 Clean Up

2.1.1 Decimate Geometry

Decimating Geometry performs a similar function to Rhino 3D's ReduceMesh command.

This function is useful to reduce the number of faces/vertices of a mesh. A surprising number of vertices can be removed without affecting the quality of a 3D print. This can be extremely useful in reducing the file-size of your mesh.

Use the Decimate Modifier, available in the Modifiers drop-down. Select Mesh > Properties Region > Settings Icon > Add Modifier > Decimate Geometry

Change the ratio field to reduce the number of Mesh Faces. A Ratio of 0.1 will reduce the number of faces by 90%.

Click apply once the changes are satisfactory.

See the Tutorial below for more information:

https://youtu.be/W9B43k9EWVMyoutu.be

Figure 2.1.1 - Decimate Modifier Blender Tutorial (Source: Yan Sculpts)

2.1.2 Fill Holes

Blender is extremely good at filling in holes to convert an open mesh in to a closed mesh

Useful to fill in small holes (open faces) in a mesh.

2.1.3 Make Faces Planar

Planarizer is an Add-On for Blender which can be downloaded from GitHub.

Planarizer allows a user to select individual mesh faces (quads or tri's) and their vertices. A Plane is constructed from the position of these vertices. When the planes of adjacent quads do not align (are not parallel) these faces are said to be non-planar or non-co-planar.

Once Planarizer has been installed, use the W key to open up the Specials Menu. From this menu, select Planarizer.

Select the vertex which is out of alignment, click w > planarizer and then in the Mesh Tools > Planarizer menu, select Anchor To: Connected Vertex.

The Planarizer algorithm works best if the user works away from the 3d cursor (starting at the edge closest to the cursor and moving away from that point).

See the Tutorial below for more information:

Figure 2.1.3 - Blender Planarizer (Source: Mark Riedesel)

2.1.4 Split Model (Bisect Tool)

1. Ensure Blender is currently in Orthographic View [Numpad: 5]

2. Switch in to Edit Mode Tab > Edit Mode

3. Select the Bisect Tool Tools > Add > Bisect

4. Draw a line as desired through the model

5. Check the Fill option Plane Normal > Fill

6. Select the Inner Region Select > Select Loop Inner Region

7. Seperate the currently selected object. P > Selection

See the Tutorial below for more information:

Figure 2.1.4 - Blender Bisect (Source: Gamemaker Game Programming Course)

Note: Model will only be a shell and needs to be made solid prior to 3D printing

2.1.5 Delete Loose Geometry

Occasionally in the process of generating meshes using software packages such as Rhino 3D, disjoint meshes can be created. It can be difficult to spot the disjoint faces which may be floating far from the rest of the geometry.

These disjoint or disconnected meshes can cause problems when trying to import a mesh in to a printer software - as the software may think the object is too large to print.

Blender is the perfect software to remove loose faces.

In [Edit Mode] go to [Menu], [Clean up], [Delete Loose] to remove unconnected and unwanted vertices and edges and faces if needed.

2.1.6 Dissolve Degenerates

Degenerate faces are polygons with an area of zero (0). A polygon is constructed as a face between three or more points. Degenerate faces are polygons which have been constructed as a face between one or two points. These faces can result in errors when the model has been created for 3D Printing.

Blender can easily remove degenerate faces.

In [Edit Mode] go to [Menu], [Clean up], [Degenerate Dissolve] to delete edges of 0 length and faces with 0 area.

​For more information refer to the Blender Manual:

https://docs.blender.org/manual/en/dev/modeling/meshes/editing/cleanup.htmldocs.blender.org

2.2 Smoothing

Smoothing can be used to create softer geometries.

Autosmoothing is a simple method of smoothing by splitting edges . This creates less featured (facetted) meshes. In Blender Auto Smooth can be enabled in Panel > Properties editor > Object Data. The Angle can be changed for more or less aggressing smoothing.

2.2.1 Smooth

In [Edit Mode] go to [Menu], [Mesh], [Vertices], [Smooth Vertex], to smooth sharp edges. This is done by averaging the angles between different faces. Amount of smoothing can be controlled by selecting number of iterations of smoothing.

2.2.2 Laplacian Smooth

In [Edit Mode] press[w], select [Laplacian Smooth]to smooth sharp edges.

Laplacian smoothing operations preserve the original shape of the item better, while also smoothing mesh surfaces satisfactorily. Laplacian smoothing uses the following algorithm:

$${\displaystyle {\bar {x}}_{i}} = \frac{1}{N} {\sum_{j=1}^{N}{}}{\bar {x}}_{{j}}$$

Where is the number of adjacent vertices to node, is the position of the -th adjacent vertex and is the new position for node.

For more information on Smoothing using Blender, refer to the Blender Reference Manual:

https://easyblend.org/html/modeling/meshes/smoothing.htmleasyblend.org

3.0 Other Resources

Figure 3.0 - 3D Filters in Blender (Source: Thomas Sanladerer)