7. Computer Controlled Machining¶
Global Class¶
This week’s global session brought together two complementary perspectives on machining.
Tony Schmitz introduced the fundamentals of CNC machining from an engineering and manufacturing perspective.
Tom Bodett, a lifelong woodworker and founder in Vermont, followed with a craftsman’s view on how digital fabrication fits within traditional woodworking practices.
Computer controlled machining is a subtractive manufacturing process using a rotating cutting tool.
As the tool moves through the material it shears away small fragments called chips, gradually shaping the final object according to the digital design.
As Tony Schmitz put it, machining is a competition between the tool and the material — and in the end, the material always wins.
Because of these physical constraints, successful machining depends heavily on choosing the correct parameters, commonly referred to as speeds and feeds. These determine how aggressively the tool interacts with the material and strongly affect surface quality, machining time, and tool lifespan.
The most important parameters include:
- cutting speed — the velocity of the cutting edge relative to the material
- feed rate — the speed at which the tool advances through the material
- chip load — the thickness of material removed by each cutting tooth
The machines typically used in Fab Labs are 3-axis CNC routers. More advanced systems may add rotational axes, enabling 4-axis or 5-axis machining, which allows complex geometries and surfaces to be produced.
Another important aspect of machining is the direction of milling.
Up milling (conventional milling) begins with a near-zero chip thickness that gradually increases during the cut. Down milling (climb milling) begins with the maximum chip thickness and decreases as the tool exits the material. Down milling often produces smoother surface finishes because the cutting force reduces toward the end of the cut.
Tom Bodett’s perspective added an important reminder: CNC machines are extremely powerful tools, particularly when producing large structures or repeated parts. However, machining itself is only part of the making process. The CNC machine removes the bulk of the material and produces precise shapes, but the craft continues afterwards through finishing, sanding, assembly, and detailing.
In other words, when the machine stops cutting, the real making often begins.
Local Class¶
Introduction to CNC machining¶
The local session focused on understanding CNC machining workflows and the preparation steps required before operating the machine.
CNC machining provides higher dimensional precision compared to processes such as laser cutting or 3D printing. Tolerances are tighter and parts can be produced with greater structural accuracy.
A rule of thumb introduced during the session was that machining projects are typically divided into three equal phases:
1/3 design
1/3 machining
1/3 post-processing
This highlights that time must be distributed across design preparation, machine operation, and finishing work.
CAM Setup in RhinoCAM¶
During the local session we focused on preparing toolpaths using RhinoCAM.
The workflow starts by selecting the appropriate cutting tool and defining machining parameters such as spindle speed, feed rate, and tool geometry.
This step is critical because the selected tool defines how material will be removed. The diameter, flute length, and cutting parameters influence cutting forces, surface finish, and machining time.
Defining the Stock¶
Before generating toolpaths the material stock must be defined.
This step establishes the size and position of the raw material block that the CNC machine will remove material from.
In this case the stock was defined as a rectangular board matching the dimensions of the plywood sheet we plan to machine.
Selecting Machining Regions¶
Once the stock is defined, the next step is selecting the regions that will be machined.
Different layers were used to organize the machining operations:
- profiling
- screws / hold-down points
- pocketing
- engraving
Separating geometry into layers makes the CAM workflow easier to control and debug.
Profiling Toolpath¶
The profiling operation defines the outer contour of the part.
This toolpath is usually executed last, once all internal machining operations are complete.
Tabs or bridges can be added to prevent the part from moving during the final cut.
2.5 Axis Machining Strategy¶
The example used a 2.5-axis machining approach, where the tool moves in X and Y while stepping down incrementally in Z.
This approach is common for CNC routers working with sheet materials such as plywood.
3-Axis Machining¶
For more complex geometries the workflow can move to full 3-axis machining, where the tool follows curved surfaces.
In this case the toolpath begins with roughing passes to remove large volumes of material.
Roughing and Finishing¶
The final step demonstrated a typical workflow used in 3-axis machining:
- horizontal roughing to remove most of the material
- parallel finishing passes to achieve the final surface.
Finishing operations typically use smaller stepovers (around 20–25% of tool diameter) to achieve smoother surface quality.
Material¶
Each student receives a single sheet of material for the assignment.
The typical Fab Lab sheet size is approximately:
1220 mm × 2440 mm
For the assignment the design should occupy roughly a 1 meter by 1 meter area of the board to demonstrate the use of large format CNC machining.
Weekly Assignment¶
The assignment for this week is to design, mill, and assemble something large using CNC machining.
For the Asfalt project, the proposed direction is to prototype a structural component of the cooking system: a CNC-cut hood structure designed to sit above the griddle.
The reference dimension for the cooking surface is:
900 mm × 600 mm griddle.
The hood structure can be designed as a simple flat-pack assembly made from plywood.
Proposed components:
- back panel
- left side panel
- right side panel
- top panel
Material:
18 mm plywood sheet.
The panels can be joined using slot joints or tab joints that allow the structure to be assembled without complex hardware.
This prototype will help evaluate:
- CNC milling accuracy
- slot-fit tolerances
- assembly behavior
- structural stability
The assignment will also demonstrate the full CNC workflow:
- CAD design
- CAM toolpath generation
- CNC machine setup
- machining process
- assembly and finishing
Documentation for the final assignment will include:
- CAD design files
- CAM toolpaths
- description of machine setup and parameters
- machining process and challenges
- final assembly
- a “hero shot” of the finished object