With SubD, I only went back until 2021, so that’s my short “tool/approach” primer for that subject. Again, if you think something’s missing/wrong, please chip in.
Display
- For SubD surfaces in Rhino, there are two display modes, unlike with NURBS surfaces: The Tab key toggles the display between box mode (control cage) and smooth mode. Most manipulations are usually best done in box mode. Use the Shaded display mode with SubD wires, SubD boundaries and SubD creases toggled on for viewing and manipulations. F10 and F11 toggle a SubD surface’s vertices between visible and invisible.
Select
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Vertice(s): SHIFT + command/CTRL + click vertice(s).
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Vertice loop: SHIFT + command/CTRL + click (end) vertice, and SHIFT + command/CTRL + double-click adjacent vertice.
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Vertice loop range: SHIFT + command /CTRL + click vertice, and SHIFT + command /CTRL + click non-adjacent vertice along vertice loop, and SHIFT + command /CTRL + double-click adjacent vertices between.
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Edge(s): SHIFT + command/CTRL + click edge(s).
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Edge loop: SHIFT + command/CTRL + double-click edge.
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Edge loop range: SHIFT + command/CTRL + click edge, and SHIFT + command/CTRL + clicknon-adjacent edge along edge loop, and SHIFT + command/CTRL + double-click edge between.
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Face(s): SHIFT + command/CTRL + click face(s).
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Face loop: SHIFT + command/CTRL + click face, and SHIFT + command/CTRL + double-clickadjacent face.
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Face loop range: SHIFT + command/CTRL + click face, and SHIFT + command/CTRL + click non-adjacent face along face loop, and SHIFT + command/CTRL + double-click adjacent face between.
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Control point(s): Click control point, and SHIFT + click more control points.
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Control point loop: Double-click control polygon.
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Control point loop range: Click control point, and SHIFT + click non-adjacent control point, and SHIFT+ click non-adjacent control polygon between.
Transform
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You can move, rotate, and scale single or multiple faces, edges, and vertices using the Gumball or arrow keys (nudge keys) after selecting them, or using the classic Move tool.
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Use SetPt to planarise vertices and edges.
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Use Slide to move edges or edge loops along the SubD surface.
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With SoftTransform (an on-off toggle), you can transform selected vertices, faces, or edges with a fall-off influence radius.
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Create
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3DFace creates a single face. Always use the Quad option. A single face has four vertices and four edges.
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SubDPlane creates a plane with 1, 4, 9, and more faces.
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SubDBox, SubDSphere, and SubDCylinder are ready-made closed SubD surfaces that you can further manipulate and augment. For a nearly perfectly circular cylinder, use a minimum of 8 faces.
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SubDSweep1, SubDSweep2, SubDLoft and Revolve generate SubD surfaces also. When using NURBS curves for these tools, you must apply MakeSubDFriendly to the curves first. Your curves will change their shape.
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With ExtrudeSubD, you can extrude edges or faces in the X, Y, Z or the U, V, N direction. Multiple faces will be extruded according to their vertice normals, edges according to a mix of face normals and vertice normals (possible bug).
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You can also extrude edges or faces with the Gumball. Set the Gumball to Align to Object to extrude in the face normal direction. Multiple edges or faces will be extruded in a linear fashion. Using the Gumball scale handle while pressing SHIFT + command (macOS)/CTRL (Windows), you can build flanges or lips from open edge loops.
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OffsetSubD offsets a SubD surface to create wall thickness.
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Refine
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Subdivide adds new faces in both U and V directions.
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Bevel inserts one or more faces or face loops along one or more edges or edge loops. The effect is like filleting NURBS surfaces.
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For a constant sharp or a soft/fading crease with user-defined values per vertex, use SubDCreaseand select consecutive edges. To remove a crease use RemoveCrease. You can also crease vertices to obtain sharp corners.
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Inset inserts new faces into existing faces. You can also inset on the fly using the Gumball, while pressing SHIFT + command (macOS)/CTRL (Windows) to select one or more faces, then dragging one of the scaling handles.
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InsertEdge adds a new edge loop or ring, or a partial one, on one or both sides of an existing one. For a partial edge loop or ring use the Range option. Use the Proportional mode with a value of, for example, 0.5 to insert at 50% of the distance.
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SubDExpandEdges inserts new faces on one or both sides of an edge. Using only one side on an object’s edge resembles applying a G2 continuous fillet in NURBS surface modelling.
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InsertPoint adds new vertices and edges. Work in Box mode and press F10 to reveal the vertices for more accurate snapping.
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Bridge inserts new faces between equal numbers of open (naked) edges or existing faces. You can choose the number of insertions and straightness of the interconnection.
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For a rectangular hole, Inset a face, soft or hard crease the four diagonal edges, and then delete the central face.
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For a circular hole, create a SubDCylinder with 8 faces and no caps, and place it centred on a square region with 4 x 4 faces, with 2 x 2 central faces deleted. Press F10 to reveal the vertices of both, and snap the square region’s vertices to those of the cylinder.
Fix
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Stitch fuses separate edges or vertices into one, either averaging their position, or allowing you to choose either one. The number of edges or vertices must match.
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Use Join to fuse adjacent SubD surfaces together. The sides to be joined should have the same number of edges. You can join smoothly or creased. Joined SubD surfaces cannot be exploded again like NURBS surfaces.
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To close an open rectangular shape, ensure you have an equal number of edges on both sides of the opening, then use Bridge.
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To close an open circular shape, place a 1 x 1 SubDPlane at the centre of the opening, then Subdivide it to match the number of edges of the circular shape, and use Bridge.
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To split a SubD surface into two individual parts along an edge loop, use Split with the Edge Loop option. You can also use the ExtractSrf command and select the faces to be separated, or to be duplicated. The Sub D Add Corners option creases both SubD surfaces to keep the edges/corners sharp.
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To straighten a string of edges or vertices, use Align with the To Plane option, selecting the start and end points.
Output
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For NURBS surface modelling (precise detailing, etc.), use ToNURBS with the Sub D Option. Use the Packed and Show Face Packs options to get an idea of the NURBS surface patches created. Be aware that if you have extraordinary vertices like star points (that you should avoid in the first place), you should use the G0 option to minimise distortion and bulging, and then reconstruct/match G1 or G2 using Rhino’s NURBS tools.
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For 3D printing, use Mesh and set the slider under SubD meshing parameters to one of five Adaptive subdivision levels. Set your Display mode to Shaded with Flat shading selected, so you can judge the size of facets in relation to your 3D printing purpose. For more detailed meshing controls, use ToNURBS as above, so you have Detailed Controls for more tessellation options. Again, check with Flat shading. Save your part with File > Export Selected… STL and the Binary option selected.
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For rendering, first use ToNurbs as above. Then save your part with File > Export Selected… OBJ. In the OBJ Export Options, set Geometry to Polygon mesh objects, Format to Map Rhino Z to OBJ Y, Naming to As OBJ groups, and Meshes to Welded, Export texture coordinates and Export vertex normals. Finally, set the slider under NURBS meshing parameters depending on your needs while checking the tessellation with Preview. Also here, Detailed Controls can be very useful. You may have to scale down your parts by 0,01 in some renderers so they’re 1:1 scale.
Miscellaneous
A subdivision surface (SubD) is a smoothly curved surface, represented by a coarse polygon mesh (control cage), generated by a recursive algorithm (usually Catmull-Clark) that splits (subdivides) the mesh polygons into ever smaller ones. SubD surfaces consist of vertices (points), edges, and polygons (faces) that you can manipulate in various ways and convert into NURBS surfaces to apply more precise surface modelling operations.
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Always work with “quads” (four-sided polygons), and avoid “star points” where more than four edges end.
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Before you detail your model, it’s a good idea to make a duplicate first, because SubD modelling is not parametric - there is no “construction history” or “feature tree” to easily go back to an earlier iteration.