Design for the CNC Process
Successful CNC cutting begins before a project is programmed in RhinoCAM. The geometry, material, scale, machining strategy, workholding, and method of assembly should all be considered while developing the project.
Unlike laser cutting, CNC machining can remove material at different depths and produce three-dimensional surfaces. This creates a wide range of fabrication possibilities, but also requires the digital model to be prepared with the intended machining operations in mind.
Tool diameter, material thickness, machining depth, workholding, assembly, and the order of operations all influence what can be fabricated. Features that are easy to model digitally may not necessarily be practical—or even possible—to machine with the available tools.
For complex or unusual projects, users are encouraged to discuss their fabrication strategy with Digital Fabrication Lab staff early in the design process rather than waiting until the CNC File Check Appointment.
Preparing Geometry in Rhino
Before beginning RhinoCAM, ensure that the Rhino file contains all of the geometry required to define the intended machining operations.
Geometry should be clean, complete, appropriately scaled, and organized so that individual operations can be easily identified. It is also important to consider how the project will be machined while preparing the Rhino file.
Preparing Geometry for RhinoCAM Operations:
The geometry used to model a project in Rhino is not always the same geometry required to create its toolpaths in RhinoCAM. RhinoCAM refers to the curves, boundaries, surfaces, and other geometry used to define machining operations as Control Geometry. Think of Control Geometry as the geometry that tells RhinoCAM where an operation should occur, rather than simply geometry that represents the finished design.
A fully modeled 3D object does not automatically provide RhinoCAM with all of the Control Geometry needed to create the desired toolpaths. Depending on the operation, curves, boundaries, or surfaces may need to be created or extracted from the model before beginning RhinoCAM.
- Profiling: Uses open or closed curves to define the edges to be cut. Profiles may be used to cut completely through the material or to a specified depth.
- Pocketing: Uses closed curves to define the areas where material will be removed.
- Engraving: Uses open or closed curves to define the paths the cutting tool will follow.
- Drilling: Uses points or circular geometry to define the locations of holes.
- 3D Roughing & Finishing: Uses 3D surface geometry to define the form to be machined. Additional closed curves may be used as containment regions to limit the area in which machining occurs.
When preparing a project, consider the machining operations that will be required and ensure that the appropriate Control Geometry exists for each operation. Rhino commands such as DupEdge, DupBorder, Project, and Make2D can be useful for extracting or creating toolpath geometry from an existing 3D model.
Whenever possible, organize Control Geometry on clearly labeled layers separate from the original model geometry.
Arranging Geometry on the Material Stock:
The arrangement of parts affects material usage, machining time, toolpath programming, and how securely the material and finished parts can be held during cutting.
When arranging components, leave sufficient space between parts for the cutting tool, bridging tabs, and any required fasteners. Avoid placing important geometry too close to the edge of the material.
For sheet goods, provide approximately 1 inch of additional material around the perimeter for fastening the stock to the spoilboard.
Parts should be arranged efficiently while still maintaining enough clearance for tool movement, workholding, and safe removal after machining. When multiple components are cut from the same piece of stock, consider how each part will remain secured as surrounding material is removed.
Stock Size & Finished Dimensions:
When possible, avoid relying on the outside edges of the material stock as the finished edges of a project. Material stock may not be perfectly square or precisely aligned with the machine. Instead, leave additional material around the project and use a profiling operation to cut the finished perimeter.
For projects that can be profiled completely through the material, pockets, engraving, drilling, 3D machining, and other internal features should generally be completed first. The finished perimeter can then be profiled from the surrounding stock as one of the final machining operations. This helps keep the part securely attached while the other machining operations are completed.
The CNC router has a maximum cutting depth of approximately 2.5 inches. If the material stock exceeds this depth, the CNC cannot profile completely through the material to establish the finished perimeter. For these projects, it may be necessary to prepare the stock to the required finished length and width before CNC machining, then use the CNC to machine the required features from the accessible face of the stock.
When determining the size of the material stock, consider both the geometry that will be machined and whether the CNC is capable of cutting the finished perimeter. The appropriate stock preparation strategy will vary depending on material thickness, project geometry, available cutting tools, and the required machining operations.
Before Beginning RhinoCAM:
- Verify the model’s units and scale.
- Verify that the project is oriented correctly for machining, with the intended cutting direction aligned with the Z axis.
- Remove unnecessary or duplicate geometry.
- Verify that all Control Geometry required for the intended RhinoCAM operations has been created.
- Ensure curves are complete and appropriate for the intended operation. Closed regions should be properly joined and free of gaps or self-intersections.
- Organize geometry using clearly labeled layers.
- Verify the dimensions and thickness of the intended material stock and ensure the Rhino layout corresponds to the actual stock.
- Determine whether the finished perimeter will be profiled on the CNC or established before machining.
- Verify that parts are arranged with sufficient space for the cutting tool, tabs, and workholding.
- Consider the diameter and cutting depth of the tools required to produce the geometry.
- Consider how the material and finished parts will be secured during machining.
Preparing Toolpaths in RhinoCAM
RhinoCAM is a CAM plugin for Rhino used to create CNC toolpaths and generate the machine code required to run them on the CNC router. The most common machining operations used in RhinoCAM are profiling, pocketing, horizontal roughing, parallel finishing, drilling, and engraving.
Before a CNC File Check Appointment, users are expected to review the provided RhinoCAM PDF Guide and attempt to program the operations required for their project.
A typical RhinoCAM workflow includes:
- Define the material stock.
- Establish the machining coordinate system and origin.
- Select the appropriate cutting tools.
- Create the required machining operations.
- Define cutting depths and other operation parameters.
- Add tabs or other strategies required to secure finished parts.
- Generate and review the toolpaths.
- Simulate the machining process and check for potential problems.
- Review the estimated machining time.
- Save the Rhino file with the RhinoCAM setup and toolpaths.
The RhinoCAM PDF Guide provides step-by-step instructions and recommended settings for preparing these operations.
RhinoCAM Resources:
