Week 07

Individual Assignment Requirements

• Make (design + mill + assemble) something big.
• Demonstrate 2D design development for CNC milling production.
• Describe workflows and operation for large format CNC machining.

Learning Outcomes

• Develop 2D parametric designs for CNC milling.
• Prepare files for large format machining.
• Understand stock preparation and workholding.
• Document assembly and structural stability.

1. Project Description – Modular Hexagonal Bookshelf

The project consists of a modular bookshelf with a hexagonal base geometry. The design is based on parametric modeling principles developed in Week 03, allowing flexible adjustment of dimensions and number of levels.

The structure was designed to be fully assembled without glue, screws, or additional hardware. All joints rely on press-fit tolerances calculated according to the 12 mm plywood thickness.

The modular system allows the incorporation of additional floors, making the bookshelf scalable and adaptable.

1. Parametric Design Development – SolidWorks

The bookshelf was developed using a fully parametric workflow in SolidWorks. Global variables and linked equations were defined to control critical dimensions such as material thickness, hexagonal base geometry, slot width, structural height, and floor spacing.

All dimensional relationships were exported and managed through an external .txt equation file, allowing centralized control of the entire design system. This approach ensures that modifying a single variable automatically updates all related components.

The project consists of 7 different parts, all parametrically linked to the same equation file. This guarantees geometric consistency and structural coherence across the entire assembly.

For the assembly stage, retention pins were integrated into the outer book supports to reduce mechanical wear caused by torsional stress from book weight. This reinforcement improves structural durability without compromising the modular press-fit concept.

The parametric strategy enables scalable customization, allowing the number of floors to be modified dynamically without redesigning each individual component.

2. CAM Processing and Toolpath Strategy – Fusion 360

The SolidWorks parametric parts were first imported into Fusion 360. All components were arranged on the TOP plane, matching the real plywood sheet dimensions: 1220 mm x 2440 mm.

Proper nesting was performed to optimize material usage while maintaining safe spacing between parts.

The DogBone plugin was installed and applied to all internal corners. Since CNC milling uses a cylindrical tool, sharp internal 90° corners cannot be produced. Without dogbone fillets, the rounded tool radius would prevent proper press-fit assembly.

By applying dogbone corrections, internal joints were modified to ensure accurate interlocking between components.

In the Manufacturing workspace, the cutting strategy was defined using the parameters tested during the group assessment.

Two separate 2D Contour operations were created:

• First operation: internal holes and slots
• Second operation: outer profile cutting

Although my tutor mentioned it was not strictly necessary, I chose to separate the operations as a precaution. This ensures that small internal features are completed before the final outer cut releases the part from the sheet.

Cutting parameters were adjusted to reduce material burning:

• Feed rate: 150 mm/min
• Spindle speed: 3500 RPM

These parameters were selected to prevent overheating and excessive edge charring observed during group tests.

Finally, a full simulation was executed to verify toolpath behavior, cutting order, and collision safety before exporting the G-code.

3. CNC Fabrication and Machine Setup

After completing the CAM preparation, the G-code file was exported using the post-processing tool and uploaded to the CNC router controller.

The milling bit was installed in tool position 3, and manual calibration was performed to determine the minimum Z reference.

Using the manual positioning controls, the work origin (X, Y) and the ΔZ offset were configured to correctly align the plywood sheet within the machine coordinate system.

Before starting the process, the preview function on the CNC control screen was used to verify the cutting sequence and estimated machining time.

The total estimated time was approximately 10 hours, which required dividing the fabrication into multiple cutting sessions.

Identified Error and Correction

During the first cutting attempt, an error occurred due to improper planning of the clamping system.

The layout was positioned without accurately accounting for the physical space occupied by the pneumatic clamps. The placement was estimated visually instead of measured precisely.

As a result, the CNC tool collided with one of the metallic pneumatic clamps, partially cutting it.

The process was immediately stopped, the material was repositioned, and the layout was adjusted to maintain safe clearance from all clamping components.

This experience reinforced the importance of:

• Accurate measurement of clamping zones
• Planning safe machining boundaries
• Never relying on visual estimation
• Simulating real-world constraints beyond digital models

After correcting the layout, the machining process continued successfully.

Final Reflection

Individual Reflection – Group Assignment