CNC Geometries

Become familiar with all geometry needed for the given toolpaths before exporting CAD geometry.

If necessary, it is possible to export additional geometry and “merge” it into an existing RhinoCAM file if additional geometry. Create a box that is the same size as the stock (material) you will be mounting to the CNC machine. Make sure your CAD geometry fits within this volume.



RhinoCAM can utilize both meshes and surfaces to create toolpaths.

RhinoCAM will recognize overlapping surfaces, only the portions visible from above will be milled. Vertical surfaces are not necessary.

Drive surfaces define the surfaces to be milled in the model. Check surfaces shroud drive surfaces beneath them and keep the cutting tool from cutting areas.



Curves and points for pockets, contour cuts and drilled holes should be located at the bottom of the cut to be made by the cutting tool.



To make selecting geometry in RhinoCAM easier, place geometry intended for different toolpaths on separate layers and drive surfaces on a separate layer than check surfaces.

An example layering system might be as follows:

  1. stock
  2. check surfaces
  3. containment curves
  4. drive surfaces for terrain
  5. drive surfaces for roads
  6. curves for pockets
  7. points for drilled holes of one size
  8. curves for interior contours
  9. curves for exterior contours



CAD geometry must be scaled 1:1 with the physical dimensions of the model to the created. Units must be in inches for the router and knee mill and in millimeters for the robots.

For large scale changes it is best to actually change units without scaling (i.e. if the bounding box of the model is 14 miles on one side, change that to 14 inches (do not scale it to 887040 inches)). Then, once the units are correct, scale the geometry by the necessary factor to make it the correct size for the model.

Changing the “absolute tolerance” in Rhino options/units to 0.0001 units can also solve some problems.



When you export your file, the geometry should be positioned so that the bounding box touches the Rhino world origin, and is in the positive (+) X, Y and Z quadrants.

It is important to make sure you position your geometry at the Rhino file world origin, not at the CPlane origin. If you moved the CPlane, be sure to reset it before positioning the geometry.