Vertex Normals

If your model file is encoded with valid vertex normals, they will be preserved. If they are missing, or null (0, 0, 0), we will automatically recompute them for the entire geometry. Some formats, like STL do not include vertex normals, so we always recompute them. We use a "crease angle" of 45° (normals will be smoothed together if the angle between two faces is less than 45°).

If your model appears completely black, it could indicate inverted normals. Viewing the model in Shadeless or Matcap mode is a quick way to check if normals are the cause.

If you want your model to appear with hard edges between faces, for 3D printable assets for example, you should make sure your normals are valid and your vertices are "unwelded" or "duplicated". See Flat vs. Smooth Shading for details.

Blender

Edge creasing (Shift+E) is specific to Blender and will not export correctly. The best way to export hard edges is to mark edges as "Sharp" in the Shading/UVs toolbox and then use an "EdgeSplit" modifier with Edge Angle unchecked and Sharp Edges checked. Then, apply all the modifiers (before exporting .blend) or when you export to OBJ make sure "Apply modifiers" is checked. This will split the vertices along the edges you selected.

Maya

You can control the "crease angle" of a mesh directly. Select the mesh and go to Mesh Display → Set Normal Angle... (Mesh Display → Soften/Harden Edges in Maya 2018) then choose an angle and Apply

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