The geometry that you create in Rhino or other 3D modeling program of your choosing will ultimately control the motion the cutting tool takes through the material to make your part. There are a number of different software tools that can create toolpaths from geometry. Some require a closed mesh model, like an STL file to a 3D Printer, others work only with 2D curves, like a DWG file to a laser cutter. Software that generates toolpaths for 3-axis CNC routers and mills will generally work with surfaces, meshes, curves, and points, depending on the particular toolpath motion that is being created for the machine. Some machines come with proprietary software that can make the process as simple as: importing a mesh surface, making a few decisions regarding desired part resolution, and then hitting "go" on the machine once you've secured the material. The Roland Modela 3-Axis Desktop mill that is in the woodshop is an example of this type of machine. Other machines require more involvement, both in creating the file that defines the toolpaths and in the operation of the machine itself. The process of using either of the two CNC Routers at the GSD requires you to engage in the process somewhere in the middle of this engagement and offers you the assistance of other experienced users. To be able to help you, however, we need you to start the process by creating the geometry necessary to describe your part for the mill.
A file that is suitable for Mastercam and the milling process is not necessarily the same file that you use to make renderings or to produce a model from which you can make a 3D printed part. The logic behind particular tool paths will ask for different types of defining geometry, so it's a good idea for you to know how you want the machine to remove material from the part when you are creating the geometry in Rhino that will be used to define the toolpaths. To make this easier, we do provide Template Files that embody an approach to removing material to define a surface-based model, and detail the geometry that is needed to configure this file on the "Assigning Geometry" section of Rachel's edited Copy of Setting up a Mastercam File (Videos). If you want to do more and venture beyond the template files provided, you might want to look at the page on Choosing Toolpaths of this tutorial about different toolpaths and the geometry types that are used with them.
Below, we discuss some things to consider when creating or editing geometry in your Rhino file for the milling process, including step-by-step instructions in each category. At minimum, to prepare for Mastercam, you will need to:
- Make sure you are working at the scale of the model, rather than the scale of the architectural body being represented.
- Make sure you are working near the origin of the modeling environment.
- Create the necessary geometry for the toolpaths you intend to use.
- Work with a layer organization strategy that makes it clear how the geometry will be used in Mastercam.
- Create a bounding box that defines the volume of your stock material.
- Position all geometry within the modeling environment such that a clear relationship to the machine's coordinate system is created.
Scale
Size
stuff
Units
stuff
Sometimes scaling causes issues of data loss from Rhino to Mastercam. This is especially true when the original Rhino file is in large units, such as kilometers, or miles, and the final model is very small. It is helpful in this case to change units without scaling (ie. if the bounding box of the model is 14 miles on one side, make that 14 inches by changing units; do not scale it to 887040 inches). Then, once the units are correct, scale the geometry up or down by the necessary factor to make it the correct size multiply by 12/14 to change to 12 inch model. It can also help Rhino scaling issues to set the Rhino Absolute Tolerance to 0.0001 units.
After scaling, re-”check” the geometry.
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.
Origin
Modeling and Math: Big numbers create problems when defining geometry: work near the world home 0,0,0 and there will be better fidelity to the data when saving, exporting, and opening files in other programs. This is universally true of all applications of digital fabrication, including 3D printing. Strange things can happen if the geometry is placed far from the origin.
Geometry Types
It is important that geometry be well defined. Try to be familiar ahead of time with the types of toolpaths you will use, and generate geometry accordingly. Some toolpaths are defined by surfaces, some by points, others by curves.
Surfaces
Mastercam can utilize both meshes and surfaces to create toolpaths. It recognizes overlapping surfaces (diagram) and will only mills the portions visible from above. Vertical surfaces are not necessary and can make a file more difficult to process. In Mastercam, surfaces are used in two ways: drive surfaces or check surfaces. Drive surfaces define the surfaces to be milled in the model. Check surfaces mask drive surfaces beneath them and prevent tool from cutting areas.
- very small surfaces
- edges of meshes
- which curves, surfaces to create (boundary, stock, etc)
Curves
Curves for pockets and 2D or 3D contour cuts should be located at the bottom of the cut to be made by the cutting tool. (Screen Shot)
Points
Points for drill toolpath at bottom of hole to be drilled.
Organize Layers
It is extremely helpful to organize geometry by layers and define the layers for how it will be used in Mastercam. If you are doing a series of contour cuts, put interior cuts on one layer and exterior cuts on a separate layer. You can select them as a group and cut them in order from the inside out. Keep surface milling geometry on a different layer than containment curves.
If you need to generate additional geometry after you've begun tooling in Mastercam, it is possible to export selected geometry as a new file and bring it into Mastercam using the File/Merge Pattern option.
Bounding Box
A volume that defines the size and shape of the material you will be placing on the machine to cut. Usually, this is a rectangular prism. This volume will be used later to simulate the milling operation and predict collisions, so it is important that you model its dimensions as accurately as possible to the actual material dimensions that you will be working with.
Specify Machine Origin
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.
X-axis is 48" max on onsrud router, 96" on AXYZ, __ on Roland, __ on knee mill, ?? on small robot, ?? on large robot.
Y-axis is 96" max on onsrud router, 48" on AXYZ, __ on Roland, __ on knee mill, ?? on small robot, ?? on large robot.
Z-axis is 6" max on onsrud router, 4" on AXYZ, __ on Roland, __ on knee mill, ?? on small robot, ?? on large robot.
Check File
When your file is scaled, positioned, and ready for Mastercam, run the “check” command in rhino, to make sure all geometry is valid. (Add something about checking for bad objects, naked edges, etc., inverted) Shrink trimmed surfaces. Rebuild particularly dense surfaces with fewer isocurves. Redefine particularly dense meshes so that they have a more coarse texture (keep in mind that a facet that has an edge of 1/64" across will probably not make the file look better than one that is 1/16" across, especially if the smallest tool you are using is 1/8" in diameter and you are working in foam or hardwood. The only thing it will do it make it more difficult and time consuming to work in Mastercam as there will be more data for Mastercam to process.)