The following Rhino3D part, submitted for discussion by Greg White of the engineering staff at ART is a great example of the typical 2½ and 3 axis work-flow and anatomy of a 3D model programmed for CNC machining using RhinoCAM. The component is part of a robotic arm assembly of ART’s newest 10 axis CNC plasma cutter (a similar arm is shown here).
The 3D part geometry was originally designed in SOLIDWORKS and then loaded into Rhino. The associative CNC machining strategies (i.e., the toolpaths) are designed using the RhinoCAM plugin and are saved with the Rhino part file. Any revisions to the geometry in Rhino are automatically incorporated into the toolpath strategies!
Advanced Robotic Technology (ART) designs prototype & production components for their multi-axis routers and plasma cutters in the Rhinoceros CAD system. They then use the RhinoCAM plugin from MecSoft Corporation to design their machining strategy and post toolpaths to their CNC routers for manufacturing. This illustration identifies the anatomy of a typical RhinoCAM part from ART. Each item in the illustration is listed below with details.
1. Part Geometry
Any Rhino geometry type can be used for machining including points, curves, surfaces, meshes and solids. In this example, ART uses closed polysurfaces for 3 Axis part definition, closed poly-curves and surface edges for 3 Axis containment and a variety of open and closed poly curves for 2½ Axis containment.
In this example, ART is machining a set of prototype parts grouped together in one stock piece. ART has chosen to connect the parts with tabs, in this case, modeled directly in Rhino. RhinoCAM can also add tabs automatically during 2½ Axis Profiling operations.
2. Machine Setup, Material & Stock Definition
In this example, ART shows Setup 1 containing the toolpath strategies they need to cut the parts from one side. Depending on your RhinoCAM configuration, you can add additional setups to the Machining Job Tree (see Item #4 below) to machine the parts from the opposite side of the stock.
3. Tool Library & Knowledge Base
The Knowledge Base contains all of the information for that specific type of toolpath, including feeds & speeds, tool, cutting parameters, clearances, etc. Feeds & speeds values can be assigned to a tool as well as an operation. You never have to define a tool or toolpath twice!
The machining Knowledge Base also supports Geometry Rules. This means that if you machine families-of-parts, your CAM programming can be automated from the Knowledge Base for true push-button machining!
4. Machining Job Tree
When a toolpath operation is created, it is added to the Machining Job tree in the order you wish it to be processed. For example, you can group together all operations that use the same tool (minimizing tool changes) or by operation type (i.e., drilling, roughing, finishing, etc.). When operations are retrieved from your Knowledge Base, this organization is maintained. You can post one, multiple, or all operations from your Machining Job and their order will be maintained in the posted g-code file even if the MCS Setup changes.
5. Hole Machining Strategies
6. 2½ Axis Blind & Thru Pocketing Strategies
Top view of 2½ Axis Pocketing operation
2½ Axis Pocketing operation: Control Geometry: Closed poly curve, Tolerance: 0.5, Stock: 0, Tool: 12mm End Mill, Stock: 0, Cut Pattern: Offset, Cut Direction: Mixed, Step Over: 40% of Tool Diameter, Location of Cut Geometry: At Top, Total Cut Depth: 40.5, Rough Depth: 30.5, Finish Depth: 10, Rough Depth per Cut: 5.5, Finish Depth per Cut: 3
Top view of 2½ Axis Pocketing operation
7. 2½ Axis Engraving Strategies
Engraving is an extremely versatile strategy because (a) the center tip of the tool will always follow the open or closed curve selected to control it and (b) it supports a full variety of tool types (14 actually). In this case, ART uses the 2½ Axis Engraving operation to cut two open-ended blind slots using lines as control geometry.
2½ Axis Engraving operation: Control Geometry: Lines, Tool: 5mm End Mill, Tolerance: 0.03, Location of Cut Geometry: At Top, Total Cut Depth: 10, Rough Depth: 8, Finish Depth: 2, Rough Depth per Cut: 2, Finish Depth per Cut: 2, Cut Traversal between Cut Levels: ZigZag.
Top view of 2½ Axis Engraving operation
8. 3 Axis Horizontal Roughing Strategies
If no control geometry is selected, the entire stock is cut in relation to the part, wherever the selected tool can reach. If control geometry is selected (such as closed curves), it will limit the toolpath in X and Y. In the first operation shown below, ART uses a closed loop of surface edges as control geometry and limits the Top and Bottom of the cut in the Z axis. In the second operation, a closed planar curve is used to contain the operation to a limited area of the stock and part.
3 Axis horizontal roughing: Control geometry: closed edge surface loop, Tool: 12mm End Mill, Tolerance: 0.25, Stock: 0.6, Cut Pattern: Offset, Cut Direction: Mixed, Step over: 25% of Tool Diameter, Stepdown: 3.0, Top containment: 1.0, Bottom Containment: -35.0, Engage/Retract: Ramp, Ramp, Always engage in previously cut area: YES
3 Axis horizontal roughing: Control geometry: Closed Polycurve, Tool: 12mm End Mill, Tolerance: 0.25, Stock: 0.6, Cut Pattern: Offset, Cut Direction: Mixed, Step over: 25% of Tool Diameter, Stepdown: 3.5, Top containment: 1.0, Bottom Containment: -37.0, Engage/Retract: Ramp, Always engage in previously cut area: YES
3 Axis horizontal roughing: Control geometry: closed edge surface loop, Tool: 12mm End Mill, Tolerance: 0.25, Stock: 0.6, Cut Pattern: Offset, Cut Direction: Mixed, Step over: 25% of Tool Diameter, Stepdown: 3.0, Top containment: 1.0, Bottom Containment: -35.0, Engage/Retract: Ramp, Ramp, Always engage in previously cut area: YES
Top view of 3 Axis Horizontal Roughing operation
9. 3 Axis Parallel Finishing Strategies
3 Axis Parallel Finishing is a toolpath strategy used either as a pre-finishing operation or as a finishing operation. In this method, the cutter is restricted to follow the contours of the part in Z while being locked to a series of parallel vertical planes. ART uses this strategy as a finishing operation cutting areas previously roughed out. The cutter is controlled in X and Y by the same closed poly curve used for Horizontal Roughing shown in Item 8 above) and is controlled in Z by the contour of the part’s surfaces.
3 Axis Parallel Finishing: Control geometry: Closed Polycurve, Tool: 12mm Ball Mill, Tolerance: 0.03, Stock: 0, Cut Direction: Mixed, Angle of Cuts: 90, Cutting Area Control: Tops Only, Stepover: 0.5, Z Containment Highest Z: 1.0, Lowest Z: -37.5, Entry/Exit: Linear, Cut Connections: Straight
Closeup of 3 Axis Parallel Finishing operation showing Stepover, Angle of Cut, and Cut Connections
Top view of 3 Axis Parallel Finishing operation. Notice that the cut is limited to the part’s surfaces even though the control geometry selected is a larger closed poly curve. The red toolpaths represent retracts in areas where the there is no part geometry to cut.
10. Cut Material Simulation & G-Code Posting
Hole machining and the first 3 Axis Horizontal Roughing operation is simulated.
Hole machining and the second 3 Axis Horizontal Roughing operation simulated.
The 3 Axis Parallel Finishing operation is simulated.
Cut material simulation comparison with the actual part showing tolerance bands in various colors. Tighter toolpath operation tolerances will affect the tolerance bands displayed.
More about Advanced Robotic Technology (ART)
Advanced Robotic Technology (ART) came from humble beginnings to become an international supplier of quality and state of the art CNC Router and Plasma profile machines. Now employing over 40 personnel, ART is developing machines with up-to-the-minute cutting technology locally and internationally. Today, ART is a world leader in CNC technology. Their CNC machines have enabled manufacturers to make drastic increases in productivity. Manufacturers ranging from ship and boat builders, cabinet makers, sheet metal workers, steel fabrication, plastic engineering as well as others, have been able to benefit from ART’s CNC routers and plasma cutters.
Greg White, Advanced Robotics