Overlapping faces vs. STL security check vs. clean geometry ?

Hello All.

It is nice meeting you.

I have been wondering about the positive sides of a clean geometry object, while sending it to the printers. By clean geometry I mean, no floating or unwelded vertices, no overlapping faces too!

I am writing this with the need for help on somthing. I have illustrated my question with the following render:
*The Program I use is 3ds max 2014 and modeling in quads.



ElementA - Clean and nice geometry. There are no overlapping vertices therefore no overlapping faces, therefore the printers are happy with the model and it will print nice and clean.

ElementB - Has a simple square extrusion from the front façade, and thanks to the connecting edges that goes all along the top and sides of the model, the geometry is also clean and tidy. No overlapping vertices and faces - will print with no problem.

ElementC -Things here start to get a little messy. There are more front façade extrusions, which leads to creating more supporting edges in order for the geometry to be clean and tidy, and this will also have no problem while printing.

ElementD - Here comes the problem. We have a complex façade with many extrusions and a lot of unwelded vertices!

Main question: What do you do in this situation in order to have a nice and clean geometry, or just a model which will 3D print right?! I mean, at the moment ElementC will either have overlapping faces, or it won't pass the STL check, because there are floating vertices with no suporting edges, connecting them.

You might advise to connect them together, and the problem is solved. That's right, but imagine a façade with 10 time more extrusions. This will bring more issues than time to consider (poly count, smoothing, texturing, etc.)

Any help on that matter will be greatly appreciated.

Thank you,
Kiril.

There are a couple of different answers for you. Several of the 'popular' drawing programs have an issue when there are too many items extruded from a single surface. Often, during the process of welding shells together, the program gets "lost" as to whether a shell should be part of the surface, or if it should be an independent piece. If the background is a large flat area, the programs often separate the smaller shells as independent pieces.

Shapeways uses a tailored copy of the Netfabb (Pro) program named Mesh Medic to clean the geometry of your model. If you have two overlapping shells, it tries to weld them into a single shell. It also will take any super-tiny shells (below the minimum detail setting) and remove them. This can cause part of your details to disappear, unless those details are properly welded into the surfaces. Note: even a mathematical gap of .000001 is enough for MeshMedic to think that the tiny shell is a separate part.

If you can get your details past Mesh Medic, then you can pretty much rest assured that they will print, as long as they are larger the error threshold of the material you select.

Thank you very much for the answer. The model I was worried about, printed just fine, regarding the issues I have adressed above. However, the model scale was changed, and it printed 3/4 time smaller. I guess for now, with this model size and this material(White, strong&flexible) it is OK to leave some overlapping faces in the elements. They print correct!

Regards.
Kiril