The following is a list of guidelines that must be considered when making visualizations that will be printed using 3D Systems (previously Zcorp) technology. As of this software release, no other full color 3D printer has been successfully tested with MVS output from write_VRML. You must follow the guidelines in write_VRML in addition to these additional guidelines.
These guidelines are provided to minimize printing problems. Users should fully understand the issues below or they will likely not create VRML files suitable for 3D printing. Given the cost of the raw material it is best to do it right the first time!
Many of these issues (if not heeded) will be obvious when the model is viewed in Z Corp's ZPrint software. Make sure the model is carefully examined in ZPrint before actual printing.
Internal Faces: You must avoid internal External faces. This naturally occurs when we cut a hexahedral volumetric model with plume_volume. The volumetric subset consists of hexahedron and tetrahedron cells. The external_edges module (and many others) creates the external faces of both sets of cells. This creates surfaces that are internal to the model even though they represent the external faces of each set of cells. The real problem here is that the mating surfaces of each cell set are coincident (see 4 below). This major problem and many others are resolved by the sequential_subset module.
Normals: Must have all surface normals facing outward to define a solid volume for printing (handled by sequential_subset module)
Coincident surfaces: You CANNOT HAVE coincident surfaces. If two layers (or other objects) have coincident sufaces this will result in open parts and printing problems. You must separate the parts by a small amount (recommend 0.005 inches in final printed size) which should not be noticeable visually. Z-Print's process will fuse these parts together (because there isn't sufficient gap to keep them truly separate).
Overlapping parts: This is supported. It is possible to have two closed volumes overlap each other and Z-Print will sort it out so long as 1, 2 and 3 above are still valid.
Surfaces: Must be extruded or represented as a volumetric layer. Surfaces have no thickness and if placed coincident with the top of a volumetric object will result in leaving the volume OPEN (unclosed). This will cause serious problems.
Cell Data: Another limitation is the inability to mix nodal and cell data. Since we use nodal data for so many things you should always strip out the cell data and use nodal data exclusively. You must be aware of the following:
Ensure that there are no modules connected to the Viewer that contain cell data. The safest way to ensure this is to pass questionable modules through extract_mesh with "Remove Cell Data" toggle ON. Normally you would want the "Remove Nodal Data" toggle OFF.
If you want your cell data (colors) to be displayed, pass the cell data through the cell_to_node module. However be aware that you'll still need to use extract_mesh afterwards because cell_to_node doesn't remove the cell_data it just creates new nodal data from cell data.
Typical modules that have cell data are Read_Shapefile, Indicator_Geology, Solid_3D_Set, Solid_contour_set, and most of the modules in the Cell Data library.
Explode distance: Need to ensure that there is sufficient gap between exploded layers (separate parts) so that they don't fuse together. Separation should be 1 mm (0.04 inches) minimum in the final print scale. Be aware that a 1 mm gap in the Z direction isn't equivalent to a 1 mm separation if the mating parts have high slopes. If yourmatingsurfaces have a 45 degree slope, the separation is reduced by cos(45) (~0.7). If you have higher slopes such as 80 degrees, the factor would be ~0.17. This would mean that you would need a Z gap of nearly 6 mmto ensure a 1 mm separation between parts.
Disconnected pieces: Although Z Print can print disconnected pieces, they won't retain their spatial position. Plumes that aren't connected to solid structure will just be loose pieces in the final print. This would also apply to post_samples' borings and spheres, unless they are connected by some common surface or geologic layer.
Concepts that areNOTSupported:
Pointsand Lines: Points and Lines cannot be printed (except as elements of an image used in a texture map). Lines must be converted to some 3D solid structure (such as closed tubes) and they must be of sufficient thickness to have some strength AND must not be disconnected pieces. Points should be represented as glyphs of sufficient size and not be disconnected.
Transparency: Transparency as an object property cannot be supported since Z Print's ink is printed onto opaque plaster or starch powder. The illusion of transparency could be achieved by creating a texture map that was a blend (using the image_transition module) between two different images.
Volume rendering: This is a subset of Transparency and therefore is not supported at all.
Jitter: First, you must make sure that coincident surfaces are avoided anyway. Jitter is designed into EVS/MVS to allow preferential visualization of coincident objects. With Z Printing we cannot have coincidence in the first place! Offset the desired primary object to ensure that it is visible. Remember no lines and no surfaces!
Thin sections: This is a somewhat subjective issue in that we really can't tell you the definition of too fragile?. We would recommend a minimum thickness of 0.5 mm, but depending on the width (total cross sectional area of the section) this may be too fragile or exhibit too much distortion during curing. We still want to have lenses pinch out, but if sections get very thin, the pieces may break.
Top View: You should write out the VRML file from a top view If there are any truly flat (horizontal) surfaces, this keeps them flatter and smoother. Also, it helps to keep the models with the largest dimensions in the x-y plane (rather than z). This speeds up printing.
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