Question on model topology

Discussion in 'Technologies and Hardware' started by chasecoop, May 9, 2013.

  1. chasecoop
    chasecoop New Member
    Hello, I'm a bit new to 3d printing working on my first print. I currently work in the vfx industry, so we have a lot of rules for geometric topology that seem like they can be broken in 3d printing a bit (and I'm learning the 3d print rules as I go).

    So my question is:

    I downloaded a 3d model as an example: the "batwingMinimalSurface", and noticed it had a lot of overlapping geometry/cvs/faces when you seperate it. And on that note, noticed it was a combined 3d model to beging with.

    Is this legal in 3d printing? Can the printer handle this type of overlap with geometry and components? (see attached image)


    Attached Files:

  2. Youknowwho4eva
    Youknowwho4eva Shapeways Employee Community Team
    Intersecting geometry can be printed. Overlapping can cause issues in the automated healing process. You can upload to see how the render comes out, if your model successfully uploads. You can also use NetFabb basic to removed double triangles
  3. AmLachDesigns
    AmLachDesigns Well-Known Member
    Each component you create must be a closed volume with correctly aligned Normals.

    A cube is a closed volume. If you remove one face without adding thickness to the remaining faces it is not.

    If you want to create a model from components, then the components must overlap even if it's a tiny bit. You can join them into one model or upload them grouped together and Shapeways will join them. There must be no non-manifold parts (explained here in this slightly out-of -date page).

    Now I know this probably raises more questions than it answers, but it should give you a place to ask more questions from....

    Good luck!

  4. chasecoop
    chasecoop New Member
    Good to know thanks. Now my question is, since you can have overlapping geometry printed, what does the printer do with that overlapping geometry? Say for instance you have two volumetric spheres intersecting and then combined into one piece of geometry, but the vertices are not actually connected - does it just mold that geometry together where the intersection is happening?

  5. Youknowwho4eva
    Youknowwho4eva Shapeways Employee Community Team
    The automated software automatically joins intersecting geometry. This process can cause a mess with overlapping geometry though. Intersect is fine. Face to face is no good.
  6. timcastelijn
    timcastelijn New Member
    Hi everyone,

    I have a question regarding the overlap as well. I created an array of cubes, translated over y-axis and rotated over z axis. which meas they overlap and all the cubes' bottom and top faces are in exactly the same plane. Is this what you refer to as "no good" Michael?

    The model looks OK in the upload section (it is a test - do not worry, I won't print $2800 worth of messy geometry :) ), however I can imagine that face-face intersections in the same plane are causing problems I cannot see. I can not join the objects in a CAD-package before uploading, as I want to use a script to create meshes.

    best regards, Tim
    Last edited: May 10, 2013
  7. AmLachDesigns
    AmLachDesigns Well-Known Member

    Generally, if things a) upload ok, and b) look ok in the SW render, they are ok.

    Check out the link I posted before for non-manifold issues.

    The case that youknowwho4eva is describing (I think) is where you bring 2 cubes together so that 2 faces exactly touch, i.e. the faces are in the same plane but do not overlap at all. In your example the volumes intersect so that is ok. Either yo or SW need to Boolean the objects together and they must intersect for this to be possible.