Hollowing your mesh for the Powder Printer with Rhino

Objects made on the powder printer can be more expensive than those made on our Ultimaker or TAZ printers. The best way to decrease the cost of printing on the powder printer is to hollow out your model such that it doesn’t consume more materials than it needs to.

This has to be done carefully though because if your object’s walls are too thin, they are likely to break during part removal. The hollowing process must also provide some kind of escape for material that would otherwise be contained inside a model. Not allowing uncured material to escape will dramatically increase your part’s weight without increasing its strength at all and will almost certainly lead to a broken part. Also, any volume of material that cannot be recovered from the finished print will be charged for after the object is printed, but may not show up on the object’s print estimate.

The following tutorial will show you the best ways to hollow mesh models in Rhino.

Objects with especially sharp volumes tend to create problematic self-intersections or leave gaps and holes when using NURBS offset commands. This can lead to less than ideal digital models for fabrication. One simple alternative is to hollow out a mesh model made from a printable but solid NURBS object. Start by creating a mesh from your model in Rhino with the Mesh command.

Then create objects that will be used to cut out an escape hole to the eventual interior of your model. In this example, a 15mm diameter cylinder will be used. Make sure that the two volumes have a clear intersection between them and that no edges on the two fall close (near or below the your modeling tolerance) to each other.

Note, the cylinder in this example was an arbitrary choise but the size was not. Any shape can be used, just be sure that the shape is as large as possible, and that it is never smaller than 10mm or 3/8th across. Multiple holes can be used, and can be useful in removing powder from an inner volume, but none of them should be smaller than the 10mm minimum. Larger holes are easier to remove powder from and result in faster part delivery and lessen chances of breaking your parts.

After making the hole cutting object, use the command MeshSplit to break the mesh apart along the intersection between these two volumes. You can use a mesh or NURBS object for the split, neither has a distinct advantage over the other. Delete or hide the uneeded remnant of the original mesh from the results.

Then use the command OffsetMesh on the result. Set the offset distance to nothing smaller than 2mm. Remember that the larger your offset, the stronger and more expensive your finished part will be. Also keep in mind that larger offsets can lead to more problematic self-intersections. These can sometimes be located and addressed in the model, and should be removed, if at all possible, prior to printing.

Enable the Solid option and set your Offset Distance. Depending on the direction of the mesh’s current surface normals, you may need to hit the Flip All button to switch the direction that the offset is performed in.

After the offset, you should run the Check command on the mesh to look for possible issues.

The primary issues for a printable mesh will be in “degenerate faces”, “…pairs of faces that intersect each other”, and “unused vertices”. Look for these issues, and use the MeshRepair function to attempt to fix them if you cannot clearly adjust them otherwise.

If you are unable to address these issues in Rhino, consider using Meshmixer, also located on your studio workstations, to hollow out and create escape holes in your model.