Overview
This week was about computer-controlled machining, especially CNC milling at a larger scale. Unlike laser cutting, CNC machining removes material with a rotating cutting tool. This makes it possible to cut thicker and stronger materials, but it also requires more attention to tool diameter, cutting depth, feed speed, fixturing, safety, and toolpath strategy.
The assignment required us to make something big. For my individual work, I designed and fabricated a curved wooden rib chair. The object was made from flat sheet material, but the final assembly created a three-dimensional curved structure.
Assignment
Group Assignment
The group assignment was to complete the lab safety training and test the CNC machine. We needed to understand the machine behavior by testing runout, alignment, fixturing, speeds, feeds, materials, and toolpaths.
Individual Assignment
The individual assignment was to design, mill, and assemble something big, approximately meter-scale. Extra credit options included avoiding fasteners and glue, including curved surfaces, and using three-axis toolpaths.
Group Assignment
CNC safety training and machine test
For the group assignment, we first reviewed the safety rules for using the CNC router. CNC machining can be dangerous because the spindle rotates at high speed and the machine moves with strong cutting force. Before operating the machine, it is important to understand the emergency stop button, machine boundary, material fixation, tool installation, dust collection, and safe body position.
We checked the control area of the machine before starting the job. The emergency stop button is one of the most important safety controls. I needed to know where it was and make sure I could stop the machine quickly if anything went wrong.
The CNC router was connected to a dust collection system. This is very important when cutting wood-based materials because the process produces a large amount of chips and dust.
Safety checklist
- Wear safety glasses during machine operation.
- Keep loose clothes, long hair, and accessories away from the machine.
- Do not wear gloves near a rotating spindle.
- Check the emergency stop button before starting.
- Fix the material firmly to the machine bed.
- Check that the tool is properly installed.
- Turn on dust collection when cutting wood-based material.
- Never leave the CNC machine unattended while it is cutting.
- Look, listen, and smell during machining to detect problems early.
Machine test
Before cutting the final design, I first made a small test cut on the wooden sheet. This test helped me check whether the material was fixed properly, whether the toolpath direction was correct, and whether the CNC machine could cut the board cleanly.
This step was important because CNC machining is not only about the digital file. The actual result also depends on the tool, the material, the cutting depth, the feed speed, and the fixation of the board.
| Test item | Purpose | Observation |
|---|---|---|
| Runout | To check whether the rotating tool is centered and stable. | A stable tool rotation helps improve cutting accuracy. |
| Alignment | To check the relationship between machine axes and the material. | The material must be squared and aligned before cutting. |
| Fixturing | To prevent the material from moving during machining. | The sheet must be fixed firmly before starting the job. |
| Speeds and feeds | To test the cutting quality and machine stability. | Incorrect settings can cause chatter, burning, or poor edge quality. |
| Toolpaths | To compare inside cuts, outside cuts, and cutting order. | Toolpath order and offset direction directly affect the final fit. |
Individual Assignment
Designing and making a CNC-milled rib chair
For the individual assignment, I designed and fabricated a curved wooden chair structure using CNC machining. The assignment required us to make something big, so I chose to make a chair-like structure from a large wooden sheet. My goal was to explore how flat CNC-cut parts could be assembled into a three-dimensional curved form.
The final design is a rib chair. It is made from repeated curved wooden ribs, side frames, and interlocking slots. Although every part was cut from flat sheet material, the assembled object creates a curved seat and backrest structure.
Design idea
The idea for this project started from exploring how CNC machining could be used to create a chair with a curved and lightweight structure. Instead of making a solid chair body, I wanted to construct the form by combining repeated rib-like components with side frames, so that the final object would feel both structural and visually open.
I first developed the chair in Blender to test the overall form, proportion, and the relationship between the curved ribs and the side frames. This helped me understand how the chair could be assembled from individual CNC-milled parts while still maintaining a cohesive shape.
Before fabrication, I also visualized the design as a finished furniture product. These renderings helped me imagine how the chair could appear in a real interior setting and as a standalone product object.
This design direction allowed me to explore one of the strengths of CNC machining: transforming a flat wooden sheet into a precise set of parts that can be assembled into a much more spatial and expressive object.
Toolpath design software
After preparing the 2D layout, I imported the file into the toolpath design software. In this step, I checked the outline of each part and prepared the cutting paths. The software was used to define how the CNC tool should follow the geometry.
This stage was especially important because the CNC end mill has a real diameter. The toolpath needs to compensate for the tool width. Internal slots and external profiles must use the correct cutting side.
CNC working software
After the toolpaths were prepared, I opened the job in the CNC working software. This software shows the machine path, coordinates, and generated G-code. I used this interface to check whether the file was correctly loaded and whether the machine movement matched the expected cutting layout.
Cutting parameters
Before machining, I set the cutting parameters in the CNC software. The visible settings included a 3.0 mm tool width, 22 mm material height, 12.46 mm cutting depth, 3 mm maximum step-down per pass, 2 mm/s machining speed, and 10000 RPM spindle speed.
| Parameter | Value used | Purpose |
|---|---|---|
| Tool width | 3.0 mm | Defines the cutter diameter for toolpath compensation. |
| Material height | 22 mm | Sets the stock height in the software. |
| Cutting depth | 12.46 mm | Total cutting depth used for the job. |
| Step-down | 3 mm per pass | Limits the cutting depth of each layer. |
| Machining speed | 2 mm/s | Controls how fast the tool moves through the material. |
| Spindle speed | 10000 RPM | Controls the rotation speed of the cutting tool. |
Machine and material setup
The wooden sheet was placed on the CNC machine bed and fixed before machining. Good fixturing is necessary because any movement of the board during cutting can damage the material, the tool, or the machine.
I also checked the tool bit before starting. The cutting tool had to be installed properly, and the tool position had to match the material surface and the machine origin.
CNC milling process
During machining, the CNC router followed the generated toolpath and cut the chair parts from the wooden sheet. The dust shoe covered the cutting area and helped collect wood chips while the end mill moved along the designed curves.
I monitored the cutting process carefully. I checked the sound of the spindle, the movement of the gantry, the dust collection, and the quality of the cut. If the material moved or the toolpath was wrong, the whole job could fail.
CNC milling result
After the CNC cutting process finished, the chair components were still located inside the wooden sheet. At this stage, I could clearly see the curved ribs, side frames, and slot details cut by the machine. Before removing the parts, I checked whether the main outlines and connection details were complete.
Removing the parts
After checking the cutting result, I removed the parts from the wooden sheet. This step needed to be done carefully because the ribs and side frames were long and curved. I separated the parts from the remaining board and checked whether the slots and edges were usable for assembly.
Assembly
The final chair was assembled from the CNC-cut wooden parts. The repeated ribs were inserted into the side structures through slots. Because the design used many curved strips, the assembly process required careful alignment and patience.
The most important part of assembly was the fit between the ribs and the slots. If the slots were too tight, the parts were difficult to insert. If they were too loose, the structure would not be stable. This made me understand how important tolerance is in CNC furniture design.
Final result
The final result is a curved rib chair structure made from CNC-cut wooden sheet material. The chair shows how flat sheet material can become a three-dimensional object through repeated ribs, interlocking joints, and careful assembly.
The final object still needs further refinement in edge finishing and tolerance control, but the overall structure was successfully fabricated and assembled. This project helped me understand the full workflow of CNC machining, from digital layout and toolpath preparation to machine setup, cutting, part removal, and assembly.
Problems and Solutions
| Problem | Reason | Solution |
|---|---|---|
| The chair had many curved parts. | The design was not a simple rectangular press-fit object, so the parts were harder to organize and assemble. | I separated the structure into repeated ribs and side frames, then checked the assembly logic before cutting. |
| The slots needed accurate tolerance. | If the slots were too tight, the parts could not be inserted; if they were too loose, the structure would become unstable. | I adjusted the slot size according to the material thickness and tested the fit during assembly. |
| The cutting file needed correct offset direction. | Inside and outside contours require different toolpath compensation. | I checked the toolpath preview before machining and confirmed which lines should be cut inside or outside. |
| The wooden parts had rough edges after cutting. | CNC machining removes material mechanically, so small burrs can remain on the edges. | I cleaned the parts manually after cutting and before assembly. |
| The material sheet had to stay fixed during cutting. | Large sheet material can move if it is not held securely. | I fixed the sheet on the machine bed and monitored the cutting process carefully. |
What I Learned
This week helped me understand the difference between designing for a screen and designing for a machine. In CNC machining, the tool has a real diameter, the material has real thickness, and the machine has physical limitations. Therefore, every small design decision can affect the final result.
I also learned that fixturing and safety are not secondary steps. They are part of the fabrication process. A well-prepared design can still fail if the material is not fixed properly or if the toolpath is not checked carefully.
The most important lesson was that CNC machining requires a complete workflow: design, material measurement, joint design, toolpath preparation, machine setup, cutting, post-processing, and assembly.
Reflection
This week helped me understand CNC machining as a complete workflow, not just a cutting process. I had to think about the design, the material, the tool diameter, the cutting parameters, the toolpath, the machine setup, and the final assembly at the same time.
My biggest learning was that a CNC object must be designed for the machine. The shape can be creative, but it still has to respect the real limitations of the cutting tool and the material. The round end mill, the cutting depth, the slot tolerance, and the assembly order all affected the final result.
I also learned that curved structures can be made from flat sheet material by using repeated rib components. This was very useful for me because it connected digital modeling with physical fabrication. The final chair was not simply a flat-pack object; it used flat parts to create a curved spatial form.
Compared with laser cutting, CNC machining felt more powerful and more demanding. It can produce larger and stronger objects, but it requires more safety awareness, more preparation, and more careful checking before cutting.