I saw a student designing a Celtic weave pattern and remembered a Freestyle technique I learned from Vince Haley in his lovely presentation "Geometries that delight". http://communities.ptc.com/docs/DOC-3318. Could PTC Creo Freestlye create this pattern?
At the same time I am in the middle of writing an article on 3D modelling for schools and one of the unique selling points (USP) for 3D printers is they can build objects that would be very difficult or impossible to make using other methods.
The model above has two separate parts woven together. Using traditional manufacture, the first part could be fabricated from strip material formed into shape and joined together. The second part is more difficult as it needs to be interwoven as it is formed.
As long as there is clearance between the parts, most 3D printers will build assemblies. In this case it shouldn't be too difficult to remove support material.