I have designed my model from the ground up and only used boolean modifier to connect the different parts of the model. Unfortunately after using the 3D Printing Toolbox to make the model manifold it deletes a great part of that model. I tried recalculate normals and it did not make any difference. I can also upload the model if necessary. But in general I would like to know what other steps I could use to "save" my model. It is not very complex either.

Thank you.

Url to file:

Update: Just in case anyone has the same problem. I had copies of the different parts of this model (before I used union on the boolean modifier) and used the Knife Project Tool to cut into cylinder and thus got a useable mesh in the end. For the smaller holes I still used the boolean and got away with it.

Thank you Mentalist for the detailed explanation.

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    $\begingroup$ imho, hearing the workflow used, only (a lot of) manual intervention could "save" your model, ie, if I got it well, "make it manifold" because "now it is not manifold" (right?) Automatic "solving" like that you used could work perhaps but for sure cannot understand the "logic" of the mesh as you intended... this it will easily "destroy" (as you see it) part of your model... If you can share it, it will be easier to suggest a path to solve (or to rebuild it better) $\endgroup$ – m.ardito May 29 '17 at 12:45
  • $\begingroup$ You can share the file here: blend-exchange.giantcowfilms.com $\endgroup$ – cgslav May 29 '17 at 13:48
  • $\begingroup$ i added the url to the file in my post $\endgroup$ – digit May 29 '17 at 14:31
  • $\begingroup$ I see. Do you need to print this? did you try to print or at least import it in printing software (and which)? $\endgroup$ – m.ardito May 29 '17 at 14:59
  • $\begingroup$ I need to print this, but before I send that I have to make it manifold. So no I did not import that to any software. $\endgroup$ – digit May 30 '17 at 9:43

How to find non-manifold geometry

From within Edit Mode, using Vertex selection, with no geometry selected, use the menu to navigate to Select > Select All by Trait > Non-Manifold. (The keyboard shortcut is ShiftCtrlAltM)

This will show you which part of your mesh is non-manifold.

What is non-manifold geometry?

Geometry is non-manifold if it doesn't form a single volume. Examples include internal faces, edges that don't form a face, vertices that don't form a face, two volumes connected at an edge or at a vertex.

Examples of non-manifold geometry

Why booleans are not (usually) the answer

The problem is that you tried to model everything with booleans instead of actually taking the time to model a proper mesh. To make things worse, some of your geometry was very dense, and very dense geometry is more likely to cause problems when booleaned.

Instead, try to model it one area at a time, using as many quads as possible:

Bad topogoly versus good topology

I'm oversimplifying with labels of "bad" and "good" for the sake of simplicity here.

The Mirror Modifier is just there to save time modeling, since this is a symmetrical shape.

Here's a list of the operations I used to create the mesh in my example: Extrude, Loop Cut, Delete (faces), Fill (faces), Snap (to vertex), Merge, Add (Circle), Bridge Edge Loops, Remove Doubles, Recalculate Normals, Crease. While that might seem like a lot to learn, these are operations you will use over and over, so they are worth getting comfortable with. It's likely you know some of them already.

While in Edit Mode you can select an edge and press ShiftE to add a crease to it. Typing 1 at this point gives the edge full sharpness and keeps the edge sharp even when a SubSurf Modifier is on the mesh.

You can later readjust the crease weight under the Edge Data section of the Properties Panel (a.k.a "the N Panel"):

Edge Crease Weight Slider

Tip: In Edit Mode you can select an Edge and press ShiftG to select "Similar" edges, like those that have the same "Face Angles", and in this way select all the 90° edges at once so that you can crease them. It saves time.

There is no real substitute for a mesh with good topology. By learning to create better topology you will be able to make many more types of models, without encountering these kinds of problems. There may be some cases where you can get away with using booleans, but keep your mesh density lower in order to reduce the risk of problems like the one you experienced.

  • $\begingroup$ Thank you, and how can I make it manifold ? $\endgroup$ – digit May 29 '17 at 13:15
  • $\begingroup$ Thanks. I knew this, but I don't know how to clean it up. The Toolbox removal algorithm removes too much. Doing everything by hand is very cumbersome. Therefore I would like to find out what other opportunities I have to do automatise this or at least prevent it from happening. I have done different models the same way and did not have problems. This time something does not work. And I don't know why. Hope that makes things clearer. Thanks again $\endgroup$ – digit May 29 '17 at 13:48
  • $\begingroup$ Ok, great thanks. This looks like retopology to me. I have not used it that often and am wondering if this could be a quick fix for my problem. Also I tend to model in cubes, cylinders etc. and than use boolean because it is intuitive and then add them. But it seems this is wrong and I should extrude (?). What is the smartest, fastest way to model something that is symmetrical only on one axis, like my model ? I don't know how to properly extrude from a "cubes" to round shapes. Sorry for asking this vague question, but I don't know how to address this different. $\endgroup$ – digit May 30 '17 at 9:40
  • $\begingroup$ @user413734 If you make it with proper topology from the beginning it's not retopology. But if you have a mesh with poor topology that you want to fix by rebuilding it differently, that is retopology. While I can't author a full-blown tutorial here, I added to the answer a list of operations I used to create my example mesh. If you get on YouTube and learn one of these a day for the next week, you'll be able to make what I made. For straight-to-curved geometry you wouldn't extrude, but Bridge, Fill, or Merge verts so that the edge count on the circle matches the edge count on the square, etc. $\endgroup$ – Mentalist May 30 '17 at 13:16

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