WEEK 07 – Computer-Controlled Machining

Objective

The objective of the individual assignment is to design and fabricate a large object using a CNC machine.

For this assignment, an initial large wooden table was designed using press-fit joints and plywood sheets. However, during the design validation process, several structural and assembly limitations were identified. For this reason, the project was redesigned and developed as a CNC fabricated bench.

Step 1 – Identify the Components

The first step of the design process was to define the structural components that form the object.

• Top surface
• Side supports
• Cross supports

These components were designed to provide structural stability and allow assembly using press-fit joints without screws or glue.

Step 2 – Define Material Thickness

The design was planned using plywood with a material thickness of 15 mm. This value was important because all slots and joints were dimensioned according to the real material thickness.

• Material: Plywood
• Thickness: 15 mm
• Tolerance: 0.2 mm

Step 3 – Design the Components

Each component was designed in Autodesk Fusion 360 using parametric sketches. This allowed the dimensions, thickness, and joint clearances to be adjusted easily before CNC fabrication.

• Top panel
• Side supports
• Structural cross beams
• Press-fit slots

Step 4 – Generate Dogbone Joints

Because CNC milling tools are circular, internal corners cannot be cut perfectly square. For this reason, dogbone joints were added to the slot corners.

The dogbone geometry allowed the pieces to fit correctly during assembly and reduced interference between parts.

• Dogbone clearance: 0.2 mm

Step 5 – Assembly Simulation

Once the components were created, the assembly was simulated in Fusion 360 to verify alignment, joint position, and structural stability.

• Correct slot dimensions
• Structural alignment
• Assembly feasibility
• Stability of the final structure

During this validation stage, the first design presented some problems. The original table design did not provide enough stability in the support area, and some press-fit joints generated excessive stress in the plywood. This could cause weak connections, difficult assembly, or possible material damage during CNC machining.

Another limitation was related to ergonomics and functionality. The first design was too large and did not use the material efficiently. For this reason, the design was reconsidered and a new proposal was developed.

The final decision was to redesign the object as a bench. This new design improved structural rigidity, reduced the complexity of the assembly, optimized material usage, and offered a more functional object for real use.

Result

This assignment demonstrated the importance of iteration in digital fabrication. The first table design helped identify structural, ergonomic, and assembly problems before the machining process.

Because the initial design presented instability and inefficient material use, a second design was developed. The new bench proposal improved structural rigidity, simplified the press-fit assembly, and allowed better use of the plywood sheet.

Through this process, I learned that CNC machining is not only about cutting parts, but also about validating the design, understanding material behavior, applying tolerances, and improving the object through testing and redesign.

Bench Redesign Process

Unlike small-scale prototyping processes such as laser cutting or 3D printing, CNC machining introduces additional challenges related to material resistance, structural rigidity, machining tolerances, tool diameter limitations, and assembly precision.

For this project, an initial furniture concept was developed and evaluated inside Autodesk Fusion 360. During the virtual assembly process, several structural limitations were identified in the original design proposal, especially in relation to load distribution, connection rigidity, and the overall stability of the structure.

As part of an iterative design methodology, the original proposal was redesigned into a CNC-manufactured bench using plywood sheets and press-fit joints. This redesign process allowed optimization of the assembly system, reduction of unnecessary material usage, and improved mechanical stability.

The final result demonstrates the integration of digital fabrication workflows with parametric design strategies and CNC manufacturing processes following Fab Academy methodologies.

Step 1 – Design Concept and Functional Analysis

The first stage of the project involved defining the functional requirements of the object and analyzing possible structural configurations for CNC fabrication.

The redesign process aimed to create a compact bench that could support vertical loads efficiently while maintaining a simple assembly system based entirely on press-fit joints.

One of the main design considerations was minimizing the number of components while maximizing structural rigidity. This approach reduces fabrication complexity and improves assembly efficiency during the physical construction stage.

The circular upper surface was selected to distribute forces uniformly across the support structure, while the angled legs improved lateral stability and reduced the risk of structural deformation.

Step 2 – Parametric Design Development

The complete bench was modeled using Autodesk Fusion 360. A parametric workflow was implemented to allow rapid modification of dimensions, slot tolerances, and structural relationships between the different components.

Parametric modeling is especially important in CNC fabrication because material thickness, machining tolerances, and tool diameters frequently require design adjustments during the development process.

The model was divided into independent structural parts, including:

• Upper circular seat
• Central cross joint system
• Three angled support legs
• Internal structural intersections

Each component was designed considering assembly feasibility, material optimization, and machining accessibility.

Step 3 – Material Characterization and Joint Calibration

Before fabrication, the physical properties of the plywood material were analyzed to determine the correct slot dimensions and press-fit clearances.

Although the nominal material thickness was 15 mm, real plywood dimensions can vary depending on humidity, manufacturing tolerances, and surface finishing conditions.

For this reason, calibration tests were necessary to determine the most appropriate assembly tolerance.

Proper tolerance definition was critical to avoid loose joints or excessive insertion forces during assembly.

Step 4 – Structural Validation and Redesign Process

After completing the initial CAD model, the structure was evaluated through virtual assembly simulations inside Fusion 360.

This analysis helped identify critical issues in the original proposal, including:

• Insufficient lateral stability
• Excessive stress concentration in the joints
• Difficulty during insertion of press-fit components
• Inefficient material distribution

These observations demonstrated that the first design would present assembly complications after CNC machining.

Instead of continuing with a structurally inefficient proposal, the design was reconfigured into a more compact and stable bench geometry.

The redesign stage became one of the most valuable learning experiences of the assignment because it highlighted the importance of iterative engineering processes during digital fabrication workflows.

Step 5 – CNC Manufacturing Preparation

Once the final geometry was validated, the parts were prepared for CNC machining.

The workflow included flattening all components into a single manufacturing plane and organizing them efficiently to reduce material waste.

CAM preparation also required the generation of toolpaths compatible with the CNC router.

Several machining considerations were included:

• Profile cutting strategies
• Dogbone corner compensation
• Tab generation for part retention
• Cutting sequence optimization

Dogbone geometries were especially important because CNC tools cannot create perfectly square internal corners due to the circular geometry of the end mill.

Large Format CNC Machining Workflow and Operation

Large format CNC machining requires a complete workflow that connects digital design, material preparation, CAM toolpath generation, machine setup, cutting operation, and final assembly validation.

The process began with the 3D model in Fusion 360. The bench components were checked to confirm that all parts could be manufactured from plywood using a subtractive process. After validating the design, the parts were organized in a flat layout according to the dimensions of the available sheet material.

Before sending the file to the CNC router, the material thickness, tool diameter, cutting depth, joint tolerance, and dogbone clearances were reviewed. These parameters are important because small errors in large format machining can affect the fit of the press-fit joints and the final stability of the object.

During operation, safety was an essential part of the workflow. The plywood sheet had to be firmly fixed to avoid movement during cutting, and the toolpath was checked before starting the job. While the machine was running, the process was monitored to identify possible problems such as loose material, excessive vibration, incorrect cutting depth, or tool overload.

The CNC operation also required a clear cutting sequence. Internal cuts and slots were machined before exterior profiles so that each part remained stable on the sheet for as long as possible. Tabs were used to keep pieces attached during cutting, preventing parts from moving when the final contour was completed.

After machining, the parts were removed from the sheet, the tabs were cleaned, and the press-fit joints were tested. This final verification confirmed whether the selected tolerance worked correctly and whether the large format CNC workflow produced parts that could be assembled into a stable bench.

Step 6 – CNC Machining Process

The fabrication stage was performed using a CNC router and plywood sheets.

The machining parameters were selected according to the material properties and tool dimensions to guarantee clean cuts and accurate press-fit joints.

During machining, particular attention was given to vibration control, material fixation, and toolpath verification to prevent dimensional inaccuracies.

Step 7 – Physical Assembly and Final Validation

After machining, all parts were manually separated from the plywood sheet and cleaned before assembly.

The press-fit system allowed the structure to be assembled without screws, adhesives, or external fastening systems.

One of the most important validation aspects was confirming that the slots maintained the correct dimensional tolerance after machining.

The final bench demonstrated:

• Good structural stability
• Correct dimensional calibration
• Efficient load distribution
• Functional assembly performance

The final object also demonstrated the importance of combining engineering analysis with iterative digital fabrication workflows.

Hero Shot

Final CNC-manufactured bench fabricated using plywood, parametric design methodologies, and press-fit assembly systems.