CNC Cutting Knowledge Base

How do I prepare architectural scale models for CNC cutting?

How do I prepare topography or terrain models for CNC cutting?

How do I prepare urban context models for CNC cutting?

How do I prepare a full scale project for CNC Cutting?

Section 1

Question: How do I prepare architectural scale models for CNC cutting?

Answer: Begin by thinking of the architectural model as two primary components: the site or base and the building. The CNC router is typically best suited for fabricating the base, while the building and smaller architectural components are often better produced using laser cutting or 3D printing.

Explanation: CNC machining allows an architectural model base to represent how a building interacts with its surrounding site rather than simply serving as a flat platform. Streets, landscape features, changes in elevation, stairs, ramps, property boundaries, and other site conditions can be incorporated directly into the CNC machined base.

Architectural scale model bases typically use 2D and 2½D machining operations, including profiling, pocketing, and engraving, with 3D surfacing operations used where continuous slopes or other non-planar surfaces are required.

When preparing an architectural model base:

  • Simplify geometry that will not be visible or meaningful at the selected scale.
  • Use pocketing to create recessed building footprints, stairs, stepped changes in elevation, or other features with defined depths.
  • Use 3D surfacing to create continuous site slopes, ramps, or other non-planar surfaces.
  • Use engraving for roads, property lines, grids, or other surface information.
  • Use profiling to cut the outside edge of the model base or other features that extend completely through the material.
  • Add recesses, holes, or other locating features where building columns, structural grids, or separately fabricated components need to align with the base.
  • Consider the diameter and cutting length of the available tools when designing small or deep features.
  • Complete pockets, engraving, surfacing, and other interior operations before profiling the outside edge of the model base whenever possible.
  • Consider how the CNC machined base, laser cut components, and 3D printed components will align and assemble in the finished model.

Using the CNC router as one part of a mixed fabrication workflow can simplify machining while allowing buildings and other architectural components to be produced at a higher level of detail.

Section 2

Question: How do I prepare topography or terrain models for CNC cutting?

Answer: Begin with a clean, continuous 3D surface at the appropriate model scale. Determine whether the finished model should represent the terrain as a smooth continuous surface or as a stepped contour surface.

Explanation: Both smooth and stepped terrain models can be produced from the same continuous 3D surface. The primary difference is how that surface is machined and represented in the finished model.

For smooth terrain, Horizontal Roughing is used to remove the majority of excess material, followed by Parallel Finishing to create the final continuous surface.

For stepped or contour-style terrain, Horizontal Roughing can be used to machine the terrain as a series of horizontal elevation levels. Adjusting the machining parameters allows the spacing and detail of these steps to be controlled without creating a separate machining operation for each contour.

When preparing topography and terrain:

  • Create a clean and continuous 3D surface representing the desired topography.
  • Establish the final model scale and determine the total elevation change that must be represented.
  • Verify that the elevation change can be accommodated within the thickness of the selected material.
  • Create closed 2D control geometry to define or limit the area that will be machined.
  • Determine how the terrain should terminate at the edges of the model.
  • Consider whether vertical exaggeration is appropriate for the intended model.
  • Provide sufficient material around the terrain for workholding.
  • Avoid terrain detail that is smaller than the selected cutting tool can reproduce.
  • Consider the relationship between tool diameter, stepdown, stepover, surface quality, level of detail, and machining time.

Section 3

Question: How do I prepare urban scale models for CNC cutting?

Answer: Begin by establishing the final model scale and deciding which site features need to be represented. Determine which elements will be incorporated into the CNC machined site or base and which buildings or architectural components will be fabricated separately using laser cutting or 3D printing.

Explanation: Urban scale models are often most effective when different fabrication methods are used for different types of geometry. The CNC router is well suited to producing a flat site base with roads, blocks, property information, and other larger site features, while laser cutting and 3D printing are often better suited to buildings and smaller architectural elements that require greater detail.

Although real sites typically contain some variation in elevation, these differences are often insignificant at the scale of an urban-scale model. Unless topography is important to understanding the project, keeping the base flat can simplify CNC machining and make it easier to locate and assemble separately fabricated buildings.

The CNC portion of an urban-scale model typically uses engraving, pocketing, and profiling operations, depending on the site information being represented.

When preparing an urban-scale model:

  • Establish an appropriate level of detail for roads, blocks, property information, and other site features based on the model scale.
  • Use engraving or shallow pocketing to represent roads, streets, property lines, transit routes, or other surface information.
  • Use pocketing for recessed site features or areas that need to be distinguished by a change in depth.
  • Use profiling where portions of the site or overall model boundary need to be cut completely through the material.
  • Fabricate buildings separately using the laser cutter or 3D printer when greater detail or more complex geometry is required.
  • Consider whether locating features are necessary for separately fabricated buildings. Recessed building footprints can help with alignment, but the radius left by the CNC cutting tool may not match the square corners of laser-cut or 3D-printed buildings.
  • For many urban-scale models, it may be easier to position and glue separately fabricated buildings directly to the CNC-machined base rather than creating a recessed footprint for every building.
  • Consider how the different fabricated components will align and assemble in the finished model.

Section 4

Question: How do I prepare a full scale project for CNC cutting?

Answer: Begin by developing the project at 1:1 scale and considering how each component will be machined, connected, and assembled. Material thickness, cutting tool diameter, and required tolerances should be considered during the design process so the components can be fabricated and assembled as intended.

Explanation: The CNC router can be used to fabricate full scale architectural and interior components, including furniture, casework, design-build projects, facade studies, architectural details, templates, and prototypes. These projects often consist of multiple parts cut from sheet goods and assembled after machining, so the fabrication and assembly strategy should be considered throughout the design process.

Full scale projects typically rely on 2D and 2½D machining operations, including profiling, pocketing, drilling, and engraving.

When preparing a full scale project:

  • Model components at 1:1 scale.
  • Verify the actual thickness of the material rather than relying solely on its nominal thickness.
  • Use profiling to cut component outlines and other geometry completely through the material.
  • Use pocketing for recessed areas, joinery, or features that do not extend completely through the material.
  • Use drilling to create holes for assembly and to accurately locate workpiece hold-down screws.
  • Use engraving for labels, alignment marks, assembly information, or surface details.
  • Design joints and connections with the diameter of the cutting tool in mind.
  • Account for inside corner radii where components must fit together, using corner reliefs such as dog-bones where required for assembly.
  • Consider tolerances required for press-fit, slip-fit, or mechanically fastened connections.
  • Arrange parts with sufficient space for the cutting tool, tabs, and workholding.
  • Consider how each part will remain secured as it is cut from the surrounding material.
  • Complete pockets, holes, engraving, and other interior operations before profiling components from the surrounding stock whenever possible.
  • Include a method for identifying similar parts when the project contains many components.
  • Consider the assembly sequence before programming the toolpaths.

For projects involving joinery or repeated components, it is strongly recommended that users machine a small test piece before cutting the complete project. Material thickness, tool diameter, and machining tolerances can all affect the fit of CNC fabricated connections.