Cases

Magics excels at delivering geometry to rapid prototyping, rapid manufacturing and 3D printing machines. The leading service bureaus use Magics to get their customers’ parts into build chambers with very short lead times, often under 15 minutes. But Magics offers a lot more than file repair and STL fixing software. When you’re pushing the creative envelope by applying the 3D printing process outside of mainstream, mechanical CAD applications, Magics can be an invaluable tool.

The concept: virtual modelmaking
As you learn when you begin to work with Magics or, more often as you are looking for ways to solve the problems that other CAD solutions have pushed downstream, the fundamental currency of 3D printing is a triangle mesh. Magics has an immensely robust ability to deal with large triangle meshes, more than a million polygons on standard desktop hardware. Because Magics performs specific tasks so well, LGM has found it possible to use it not only for standard file repair and build envelope preparation, but also for what we call ‘post processing’ and ‘composting’. Perhaps a better name would be ‘virtual modelmaking’.

In addition to 3D printing on three Z Corporation 510’s, our architectural studio employs a variety of fabrication techniques, including CNC milling and laser cutting. We deal with a very diverse range of clients, but “watertight” STL files, supplied by our printing customers, represent less than 5% of our business. Most of the time we are either working with 2D geometry which we draw into 3D using a variety of architectural modeling programs, or we are receiving building geometry from programs that are designed for virtual visualization.

There are often few, if any, watertight shells, many coincident faces and a great deal of geometry built from planar surfaces. We import mesh geometry from a variety of different programs and workflows and perform ‘virtual modelmaking’ tasks within Magics prior to part fabrication. Indeed, geometry modified within Magics may be exported to CAM for machining and even to 2D laser cutting or virtual visualization workflows.

The challenge
We recently generated a model for a customer who was constructing an exhibit for the US National Building Museum in Washington DC. The model, which represented a section of a theater, had to be received at the customers’ site and assembled for review. It then had to be disassembled and shipped to the exhibit site, where it would be installed by an untrained staff just in time for the opening. The input was 3D triangle geometry created in Rhino. The combination of time frame, model requirements and input geometry dictated that we perform almost all of the geometry processing in Magics.

The transformation of a life size 3D model into a scale model for 3D printing

Because the model was drawn at ‘real world’ scale but would be built at 1/150 of that size, the first task was to cull geometry not needed in the final model. This included detail items like theatrical lighting fixtures and interior trim. The ‘shell select’ tool, as well as the ‘triangle select’ and subsequent ‘expand selection’ tools are very useful for such a task. Next we had to turn on the geometry validation tools, making flipped normals and bad edges visible. This allowed us to begin patching and hole filling.

I prefer to use the merge shells tools to create super groups of fixed geometry. In this case the groups were things like ‘stage’, ‘seats’, ‘horizontal structure’ and ‘stairs’. Here I was planning ahead, since each of these groups may have required other modifications, particularly offsets or extrusions, in order to make them strong enough for the 3D printing process. In addition, once you find that settings in the fix wizard work on one type of item like an extrusion with no end cap, it is then possible to apply the same settings to all similar objects.

The design of the assembly
Once we have separated out the geometry into its major groups, fixed the shells and performed offsets, we can begin to think about various ways in which the model can be put together. For this you need good experience with the specific anisotropic scale factors for your particular processes, as well as the offsets necessary for assembly, such as for clearance of holes and gluing seams. When in doubt, it is better to oversize holes or other features that are difficult to hand sand and to underestimate the offset for features like flat surfaces that will assemble better with a quick flat sanding.