model is. Think of it this way: all 3D models define a
space that is either “outside” or “inside” the model,
like the outside or inside of a ball. If you were to fill
the inside of a manifold ball with water, no water
would come out. There would be no holes and no
place for the water to leak through.
A non-manifold model is the opposite. Water would
leak out of a non-manifold ball because there
are holes or missing data in the 3D model. Often
non-manifold models have large holes that are easy
to see. Sometimes, though, the 3D model may look
manifold but really is not. The sphere in Figure 13-9
looks manifold upon human visual inspection, but
the software would find the problem.
FIGURE 138: A rectangular object exported to a three-sided polygonal format (STL). Note that there are no more four-sided areas.
They have been converted to triangles.
FIGURE 139: A small cut (shown in blue) in this 3D model makes
the model non-manifold.
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Without specifically using analysis tools, no amount of visual scrutiny, even if you zoomed all the way in,
would show that there was a small cut in this sphere. The slicer software that would 3D print this model
would have to make some decisions on how to slice the object for physical printing.
Luckily there is hope! Most of the online 3D printing service bureaus offer tools to repair your 3D model for
you. For the most part, these work well, but it is always better to have a good model in the beginning of the
3D printing process. That way, you are more likely to be happy with the end result.
There are a few applications that can help you repair models if your end goal is 3D printing. We believe a
very good option is the program Meshmixer, which we mentioned earlier and described in Chapter 11. The
Inspector tool in Meshmixer (click “Analysis” then “Inspector” in Meshmixer) can often fix your model in just
a few clicks, as shown in Figure 13-10.
Clicking any of the little blue bubbles coming out from the model will usually repair that part of the mesh
successfully, making the model ready for 3D printing. This tool is so easy to use, it makes Meshmixer an
ideal part of your existing workflow for 3D printing, even if you are already comfortable using other tools.
FIGURE 1310: The Inspector tool in Meshmixer pinpointing problems with the 3D model
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195 Chapter 13: Getting and Fixing 3D Models
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Meshmixer also occupies a unique position in the 3D printing world. It does an
excellent job of bridging the gap between the digital world of 3D modeling and
the physical world of 3D printed objects. No other software program has such
comprehensive tools to help you get a physical object created. If you have not
read the chapter on Meshmixer yet (Chapter 11) it would be well worth your time.
This free program will help you get more consistently successful 3D prints.
Thinking about using 3D printing to enhance or start a business? This next
section is for you! Any endeavor can benefit from 3D printing and the next
section gives a great overview of how.
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197 Chapter 14: How to Start or Enhance a Business With 3D Printing
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