Considerations when designing for 3D printing

A model must be ‘watertight’

If a 3D model contains holes or gaps it will not be suitable for 3D printing. The model must be completely closed or ‘watertight’ as it is more commonly referred to. This should be done before the model is exported as an STL file because it can be difficult to spot and fix the problem areas once it has been converted. This problem can also occur during file translation from one modelling system to another. You may wish to try Accutrans if you want to fix the problem yourself or we can give you a quotation for carrying out the work. The example below shows several ‘gaps’ in the mesh indicating problem areas.

Non-manifold objects

Non-manifold objects cannot be printed; the basic definition of a non-manifold entity would be if it has edges that are shared between more than two faces. The picture below shows an example of this.

The two cubes shown in this picture have one edge in common and therefore are shared by four faces. If you are interested in the mathematics of manifolds have a look at this article, but be warned it’s not for the faint hearted!

Normals

If your model contains inverted normals the printers will not be able to determine the inside or the outside of your model/mesh. All normals should be pointing in the correct direction. The picture below shows the normals (small blue lines) as all coming out of the model and are therefore correct. To show the surface normals in your modeling package refer to your software documentation, alternatively download Meshlab which can process STL files and show the surface normals. This Wikipedia article has more details on surface normals.

Object size
The maximum size of object will be determined by the process chosen, please refer to our materials section for more information. If your model is too large for our printers then the model can either be scaled down or broken down into smaller pieces that can be fitted together afterwards.

Minimum wall thickness

Minimum wall thickness is defined as the minimum thickness that your model should have at any given point. The pictures below give examples of a bad wall thickness and a good wall thickness that can be printed.

Example of no wall thickness

Example of a printable part

The minimum printable wall thickness will depend on the process chosen, please refer to our materials section for more information.

Why is minimum wall thickness important? Having a thin wall section will make the model very delicate and this will cause problems when we try to remove the support material and also with the general handling of the model. If there are large areas of thin wall thickness this can also causes errors with the build of the model.

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