Troubleshooting and Repairing Models

Blender is a very powerful application with capabilities that extend well beyond 3D printing. Because its goals are often grander, Blender is not always concerned with making clean, printable meshes. Sometimes your model will develop issues that will need to be repaired for better 3D printing. In this chapter, you will learn how to identify and resolve common issues. The skills include:

• Removing duplicate vertices
• Flipping bad face normals
• Locating and correcting non-manifold edges
• Enabling and using the 3D Print Toolbox add-on
• Using Windows 10's 3D Builder application to repair models

Removing duplicate vertices

Sometimes during modeling work, extra vertices are accidentally created. In Chapter 7, Customizing with Text, we talked about how setting the Extrude property for a text object before converting to a 3D mesh is likely to cause issues. The source of those issues is a large number of duplicate vertices.

Because they are in the exact same spot as other vertices, the duplicates are naturally camouflaged and hard to recognize. You may see subtle signs of their presence when you are multi-selecting with the Shift key. Normally, when you pick two vertices that are connected by an edge, that edge is also highlighted:

Normal behavior, selecting both vertices selects the related edge as well

If you select two vertices and the edge between them is not highlighted, there is something amiss. One of the vertices you selected is not part of that edge. There is a...

Flipping face normals

In Chapter 3, Converting a Bezier Curve to a Properly Sized 3D Mesh, you were introduced to face normals, which is how Blender and the slicer determine what is the inside and the outside of your object. A common issue is some of those normals are flipped so Blender would see the outside of your object as an inside. As illustrated in Chapter 3, Converting a Bezier Curve to a Properly Sized 3D Mesh, you can turn on a light blue line in the Properties Shelf to mark outside of your faces. For a normal cube, such as the cube on the left in the following image, each blue line is facing the outside. However, sometimes during your modeling process, particularly when you are making your own faces, one or more faces gets flipped. In the cube on the right, one face is missing a blue line. It is facing the wrong way and pointing to the inside of the cube instead:

The...

Finding and fixing non-manifold edges

When I first started 3D printing, the non-manifold edge was an intimidating concept to grasp. For our purposes, you can think of manifold as something that can be manufactured and become a real-life object. Everything has an inside and an outside, is connected, has a thickness, and would make sense to the 3D printer. Non-manifold, on the other hand, would be a geometry that can't exist in real life.

Exploring examples of non-manifold edges

For a more concrete way of looking at it, all your edges should be connected to two faces with matching normals. Edges that don't meet that criteria will be flagged as non-manifold. Some examples are explained in the following sections:

...

Repairing models with 3D Builder

There are a number of services available to help repair your models. Autodesk NetFabb and MakePrintable are two examples. However, if you are already using Windows 10, you need look no further than your own workstation. Microsoft's 3D Builder application is installed by default and will make repairs to models.

Not only will 3D Builder take care of issues such as duplicate vertices, bad face normals, and non-manifold edges, but it will also get rid of unnecessary internal geometry. In Chapter 4, Flattening a Torus and Boolean Union, we saw how overlapping separate objects (without doing a Boolean Modifier) would cause confusing internal geometry. 3D Builder will recognize and correct that issue as well.

To use 3D Builder in Windows 10, the steps are:

1. In Blender, go to File | Export | Stl (.stl) to save your model as an STL file. Don't...

Summary

In this chapter, you learned about common issues that could impact the printability of your model. You learned to be on the lookout for duplicate vertices and how to use Blender to remove them. You learned how to review and correct bad face normals. You learned about the tricky concept of non-manifold edges. You enabled the 3D Print Toolbox add-on and used that in your quest to identify and correct non-manifold edges. Finally, you learned how outside tools, such as the 3D Builder in Windows 10, can be used to repair your models.

Throughout this book, you have seen how Blender can be used for a variety of projects. Blender can help with jewelry projects, such as the profile pendant and the coordinate bracelet. Blender can accommodate architectural models, as seen with the house figurine. Finally, you are not limited to geometric, precisely-sized models. With the human hand...