Split Models: Rhino 3D and Physical Joining
Ways to split models
Sometimes, your model may be too large to fit the bed or you want to have a section of the model that can move. This section will cover how to split your model in Rhino 3D. It will also cover certain methods on aligning and joining these models physically.

Aligning & Connection Pins

When you split your 3D print into multiple parts, consider using aligning pins/dowels that help align your parts together. Typically, these dowels and alignment holes have a tolerance of 0.5mm.
Using printed dowels as alignment strategies.
Instead of printing dowels, consider using bits of filament as the dowel itself. This will save you time in both modelling and printing the dowels. However, this method does not produce a strong connection; it's only purpose is to align. There are two ways you can approach this, either with vertical dowels or horizontal dowels.
Using pieces of filament as an alignment dowel.

Splitting up a Model in Rhino

Your geometry can be manipulated with Boolean commands in Rhino using [BooleanSplit] for NURBs geometry and [MeshBooleanSplit] for Meshes.
While there are commands such as [MeshSplit] and [MeshTrim], note that these produce open meshes that are not closed.

Splitting Models

Any surface or plane can be used to split a mesh. The main advantage of using Rhino to perform mesh boolean splits is that models can be split along curves rather than straight lines.
To split a mesh in Rhino:
  1. 1.
    Import your model into Rhino
  2. 2.
    Draw a plane/surface where you intend to split your model. Make sure the plane/surface overlaps the model.
  3. 3.
    Type the command [MeshBooleanSplit]
  4. 4.
    Select you model, and hit enter
  5. 5.
    Select the plane as your Cutting Object and hit [enter]
  6. 6.
    The resultant meshes should be split
  7. 7.
    Meshes can now be exported as .stl files for optimal orientation for 3D printing

Adding Alignment Geometry

To add pins/sockets, use [BooleanUnion] or[BooleanDifference] or its Mesh equivalents to add alignment geometry such as nubs, pins, and their corresponding holes. You can use any sort of closed extrusions/polysurfaces/meshes for these.
Overlap the geometry within the mesh first. Dimensions shown are just an example.
Ensure you leave some tolerance in the pins to account for ease of joining and micro-imperfections due to filament width - around a 0.25mm gap will do.
To perform a mesh boolean difference operation on a mesh in Rhino:
  1. 1.
    Import your model into Rhino.
  2. 2.
    Split your model following the steps described in the previous section.
  3. 3.
    Draw the geometry where you intend to add alignment pins to your model. Make sure the box overlaps the model to ensure a successful boolean operation.
  4. 4.
    Type the command [MeshBooleanDifference]
  5. 5.
    Select your split model, and hit enter.
  6. 6.
    Select the box as your polysurface to be subtracted with and hit [enter]
  7. 7.
    The resultant meshes should have the alignment hole.
  8. 8.
    Meshes can now be exported as .stl files for optimal orientation for 3D printing