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    Manifold by design

    Nathi Tappan(nathitappan)
    posted to: Project 1: Toy Tank - Preparing for Print

    Hi there,

    I love that the add-on can help us check and fix objects that are not manifold so we can speed up the process to get to a final print. 

    I don't like, however, that in doing so we might be unaware of substantial changes that can happen my merging verts all around. If it's a tight clearance, or a very specific shape, things can get ugly on more complex models.

    I guess I'm trying to make sure I have proper understanding of what manifold is, and how to turn on the "modeling for printing" switch in my brain.

    Do I get it right that as long as all my faces have thickness and edges touch at least 2 faces I have achieved a manifold model? If I'm cautious on doing that, theoretically I can push the button on the add-on and nothing will happen, right? 

    If you have any words of wisdom of how to approach a design for optimal printing from the planning phase, or any extra resources to share, I'm all ears!

    Thanks!!


    1 love
    Reply
    • Martin Bergwerf replied

      Hi Nathi,

      "...edges touch at least 2 faces..."

      That should be all Edges are connected to exactly 2 Faces. But then that is also  the only 'rule' that decides if a Mesh is Manifold. (There are of course other definitions of Manifold, but this is probably the simplest...)

      But Manifold alone is not enough to be Printable (sharp angles, for instance are no good). The Addon checks for other problems as well, if I'm not mistaken.

      2 loves
    • Nathi Tappan(nathitappan) replied

      Good point Martin! A third face connected there would probably just be an unwanted inner face giving us all sorts of issues for printing and not printing alike. 

      1 love
    • Omar Domenech replied
      I basically picture it as something that can literally hold water. The mesh has to be tight that if you filled it with water on the inside, not even a drop will spill out. So basically no holes in the mesh. I believe that is the most essential rule for printing. 
      2 loves
    • Nathi Tappan(nathitappan) replied

      Maybe that answers one of my last questions then... whether the mesh can have 'loose parts' that intersect or not. Not sure if that would still make them "hermetically sealed".

      1 love
    • Omar Domenech replied

      I'm not sure. I would say that excess is unwanted and could possibly mess up the print or at the very least waste material? I'm not sure, we'll wait for Porter to confirm. 

      2 loves
    • Martin Bergwerf replied

      Omar, that's what people often say, that manifold means that it should be able to hold water,

      but this Mesh, for instance, is 'watertight', but not Manifold:

      Watertight.png

      2 loves
    • Omar Domenech replied

      Ah I see. I often think the word came from a guy named Manuel Fold, who everyone called Manny and so it became Manifold. 

      2 loves
    • Martin Bergwerf replied

      That might be true...I don't know.

      Here a fun fact, when a Mesh is Manifold, then the number of Vertices plus the number of Faces, minus the number of Edges is always 2.

      The opposite is not true, unfortunately, Suzanne is not Manifold, but has 507 Vertices, 500 Faces and 1005 Edges and 507 + 500 - 1005 = 2.

      2 loves
    • Nathi Tappan(nathitappan) replied

      Ha! That's a great visual Martin, thank you! But dang, how do you know those things? You and my husband would get along... he's the type that loves those fun facts.

      And Omar, I'll hold Manny's story as true in my head. Lol. 

      Fair enough, that makes sense. Let's see what Porter says...

      1 love
    • Martin Bergwerf replied

      Ha, I was wrong!

      That number 2 (V + F - E) is called the Euler characteristic of a Manifold. But the Euler characteristic of a Torus, for inmstance is 0, so it's not always 2.

      1 love