HelpTutorialsCreating Hollow Objects

Creating Hollow Objects

When you create an object with Shapeways, the order price is determined by the actual printed volume, and not by the model's bounding volume. An easy way to save some money, sometimes a LOT of money, is by making your object hollow. This short tutorial will explain the basics of hollow objects for 3D Printing with Shapeways.

There are of course some trade-offs to this trick:

  1. Hollow objects will not be as strong as solid objects.
  2. Objects such as statues may need a solid base to prevent them from tipping over.
  3. It will increase the number of polygons in your model. If this becomes a problem, you can reduce the number of polygons on the inside as it doesn't need the same level of detail as the outside.
  4. Lastly, you'll have to make sure the walls remain thick enough based on the material you select.

Hollowing a cube

I'll demonstrate the process of creating a hollow object by taking a simple cube:

In a traditional 3D application this cube will appear to consist only of six faces with empty space in between. For Shapeways however, this represents a solid volume.

The easiest approach is to make this cube hollow is to extrude the outer surface and create a scaled-down version on the inside of the object:

Hint: Simply extruding and scaling may not always give correct results - especially for objects with complicated shapes and sharp creases. You may need to do some manual fixing in these cases.

Your hole will require a hole to connect the inside faces to the external faces. Without this hole, our automated software will remove the internal geometry, and your piece will be solid when quoted and printed. These holes have to allow us to remove the support or excess material (except in the case of Transparent Detail and Frosted Ultra Detail where trapped material is allowed for visual effect). Follow the individual material guidelines for information on how big of an escape hole you will need in your model, and where it can be placed.

Finally, inspect the direction of the face normals. It's important that the face normals on the outside of the object point outwards and those on the inside point inward. Most applications will allow you to display the face normals or turn off double-sided rendering - faces with incorrect normals will usually display as a hole in the mesh.

We've published a tutorial by Bryan Vaccaro that (among other things) show how to do this with Maya.

How much did I save?

I uploaded both the solid and the hollowed cube. As they were only 2x2x2cm the prices were low, but the difference is obvious: the solid cube would cost $17.80 while the hollowed cube would cost only $3.43 - I saved 80%! Not bad, for only a few minutes of work.