PropCad: Tips for root fillets with Rhinoceros3D
Root fillets is often the most time-consuming process during CAD/CAM migration – but this feature in Rhino can help!
PropCad is often used as an intermediate step to the final CAD model of the propeller. There are often additional details included in the CAD model such as puller holes, stern seal recesses, keyway reliefs, etc. As a result, the blades and hub geometry from PropCad is often exported to a native CAD format for direct manipulation within that environment.
PropCad data is exported to native CAD formats using “macros” that call the specific CAD commands. One of the most difficult surfaces to recreate in a native CAD format is the root fillet. Fillets are highly-specialized routines and have different inputs for each native CAD environment – some fillets must be created as surfaces, while other must be derived from solid geometry.
The Rhino3D command file (*.txt) is one of the most popular CAD exports for PropCad projects. Rhino is very useful because it has sufficient tools to handle both solids and surfaces. Recently, HydroComp staff found a new, Solid-based approach to developing root fillets. This approach is considered the most-effective and most-expeditious method for adding root fillets to a propeller model.
The propeller above is a 4-blade Kaplan developed in PropCad. First, we export the propeller using the Rhino 3/4/5 macro (*.txt). The Surface Export options are used to export the blade surfaces as well as the root, tip, and edge surfaces. The hub is also exported, but the fillet (generated from PropCad) is disabled.
The Rhino macro is imported to Rhinoceros 3D (v5.12.50810) via Tools > Commands > Read from File. The first step is to join all blade surfaces (including the root, tip, and edge surfaces) into a solid using the Join ( ) command. This solid blade should be rotated and copied using Transform > Rotate to create the correct number of blades. The individual solid blades are combined with the solid hub using the Solid > Union command.
To create the root fillet, use the Solid variable radius fillet command. This command is located under the Solid fly-out context panel. The solid variable radius fillet allows you to select multiple edges, which makes creating a full-round fillet much easier than manually intersecting individual fillet surfaces for each edge.
The steps for creating the fillet are shown fully in the press release below.