Week 07 — Computer-Controlled Machining

I designed, tested, milled, and assembled a CNC-milled shell chair.

Tools used

Key outputs

Overview

This week was about CNC machining.

CNC machining cuts material with a rotating tool.

It can cut thicker material than a laser cutter.

It also needs more safety preparation.

I made a shell chair from wooden sheet material.

The chair used ribs, side frames, slots, and curved parts.

Assignment

Group Assignment

We reviewed CNC safety and tested the machine.

We checked runout, alignment, fixturing, speeds, feeds, and toolpaths.

Individual Assignment

I had to design, mill, and assemble something big.

I chose to make a CNC-milled shell chair.

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.

CNC router used for computer-controlled machining
CNC router used for this week's computer-controlled machining assignment.

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.

Power start and emergency stop buttons on the CNC machine
Control buttons on the CNC machine. The red button is the emergency stop button.

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.

Dust collection system for CNC machining
Dust collection system used during CNC machining.

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 cut on wooden sheet before the final CNC job
Test cut on the wooden sheet. I used this step to check the machine setup, material fixation, and cutting quality before machining the final chair parts.
Video of the test cut. I used this test to check the toolpath, material fixation, and cutting quality before starting the final job.
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 shell chair

For this assignment, I made a chair from a wooden sheet.

The chair was inspired by the classic Shell Chair.

I liked its open side frame and curved seat.

I did not copy it directly.

I changed the armrests and side profile.

I wanted the shape to feel calmer and more like Song dynasty furniture.

Design workflow

I started with a quick sketch.

The sketch helped me test the shell-like seat and rib direction.

Hand sketch of the shell chair concept
Early sketch of the chair idea.

Then I rebuilt the parts in Fusion 360.

I used parameters for the slots.

The board thickness was 12 mm.

So I set slot_w and slot_l to 12 mm.

Fusion 360 parameters for 12 mm slot width and length
Fusion 360 parameters for the 12 mm slot size.

I drew the armrest as a separate sketch area.

This made the upper curve easier to control.

Fusion 360 sketch of the armrest area
Armrest sketch in Fusion 360.

I also drew the seat curve with dimensions.

This helped me control the width, height, and center slot.

Fusion 360 sketch of the seat curve
Seat curve sketch with dimensions.

The last side sketch connected the seat to the legs.

This part gave the chair its main support.

Fusion 360 sketch of the support transition
Support transition from seat to leg.

After the sketches were ready, I arranged all parts into a cutting layout.

The layout included ribs, side frames, arms, and connection slots.

CNC cutting layout of all chair parts
Final part layout before CNC toolpath preparation.

I checked the full chair in Blender before cutting.

This helped me see the whole shape in 3D.

3D assembly check of the chair in Blender
3D assembly check in Blender.

I also 3D printed a small sample.

The sample helped me check the form and assembly.

After that, I sent the layout to CNC cutting.

Small 3D printed sample of the chair
3D printed sample before CNC cutting.

Toolpath design software

I exported the clean profiles as a DXF file.

Then I imported the file into the toolpath software.

I checked the outline of each part.

I also checked the cutting side of each toolpath.

This was important because the end mill has a real width.

Toolpath design software for CNC machining
Toolpath software used before sending the file to the CNC router.

CNC working software

I opened the job in the CNC working software.

I checked the toolpath, coordinates, and generated code.

This was my last software check before cutting.

CNC working software showing toolpath and G-code
CNC working software with toolpath and G-code.
CNC toolpath preview and G-code interface
Toolpath preview before machining.

Cutting parameters

I set the cutting parameters before machining.

The visible tool width was 3.0 mm.

The material height was set to 22 mm.

The cutting depth was 12.46 mm.

The maximum step-down was 3 mm per pass.

The machining speed was 2 mm/s.

The spindle speed was 10000 RPM.

CNC cutting parameter window
Cutting parameter window in the CNC software.
Parameter Value used Purpose
Tool width 3.0 mm It defines the cutter diameter.
Material height 22 mm It sets the stock height.
Cutting depth 12.46 mm It sets the total cutting depth.
Step-down 3 mm per pass It limits each cutting layer.
Machining speed 2 mm/s It controls tool movement speed.
Spindle speed 10000 RPM It controls tool rotation speed.

Machine and material setup

I placed the wooden sheet on the CNC bed.

I fixed the sheet before machining.

Good fixturing prevents movement during cutting.

I also checked the tool bit before starting.

Checking the CNC tool bit before machining
Checking the tool bit before machining.

CNC milling process

The CNC router followed the generated toolpath.

It cut the chair parts from the wooden sheet.

I watched the cutting process carefully.

I checked the sound, dust collection, and cut quality.

Close-up of CNC cutting curved component
Close-up of cutting a curved chair component.
Final cutting process on the CNC router.

CNC milling result

After cutting, the parts were still inside the wooden sheet.

I checked the ribs, side frames, and slot details.

I made sure the main profiles were complete.

CNC-cut chair parts on the machine bed
CNC-cut parts after the job finished.

Removing the parts

I removed the parts from the wooden sheet.

I did this carefully because the ribs were long and curved.

Then I checked the slots and edges.

Removing CNC-cut chair parts from the wooden sheet
Removing CNC-cut parts from the sheet.
CNC-cut parts prepared for assembly
CNC-cut parts prepared for assembly.

Assembly

I assembled the chair from CNC-cut wooden parts.

The ribs were inserted into the side frames.

The slot fit was the most important part.

Tight slots made assembly difficult.

Loose slots made the structure unstable.

Assembling the CNC-milled shell chair
Assembly process of the CNC-milled shell chair.

Final result

The final chair was made from CNC-cut wooden sheet material.

Flat parts formed a curved shell-like structure.

The design still needs better edge finishing.

The slot tolerance also needs more testing.

Final assembled CNC-milled wooden shell chair
Final assembled CNC-milled shell chair.
Final shell chair from another angle
Final result from another angle.

Problems and Solutions

Problem Reason Solution
The first DXF had too many points. Fusion 360 became slow and hard to edit. I rebuilt the main curves with cleaner sketches.
The board thickness affected every slot. The real material thickness was 12 mm. I used slot_w and slot_l as 12 mm parameters.
The curved parts were hard to understand. Flat profiles had to become a 3D chair. I checked the full assembly in Blender.
The assembly was risky before CNC cutting. A large CNC mistake wastes material and time. I 3D printed a small sample first.
The slots needed a better fit. Tight slots were hard to assemble. I checked the fit during sample assembly.

AI Use Statement

I used AI to help organize my documentation text.

I used it to make the sentences shorter and clearer.

I also used it to check the English wording and page structure.

The design, modeling, machining, testing, photos, and final decisions were my own work.

Design Files

I exported four DXF files for the main chair parts.