W7 | Computer-Controlled Machining

Safety

The safety training reinforced how important it is to give a CNC router your full attention at all times. This is not a machine that can ever be left unattended. Someone must always be present, closely monitoring the cut and listening to the sound of the spindle, since any unusual noise can be an early sign that something is wrong. If that happens, the emergency stop button must be within immediate reach so the machine can be stopped without delay. On the PPE side, safety glasses and ear protection are non-negotiable: the spindle runs at high RPM and generates a noise level that, with prolonged exposure, can seriously damage your hearing. Dust extraction also needs to be running throughout the entire job — MDF dust is harmful if inhaled over time.

For this week's assignment, I took on the challenge of designing, CNC milling, and assembling a large-scale object — approximately one meter in size. The goal was to apply everything I had learned about CNC milling, and after training with the ShopBot PRS Alpha, it was time to put it into practice. The perfect opportunity came up through a challenge proposed by one of the university's departments: creating a backlit sign featuring their logo, where each letter and the base had to be illuminated, with all the wiring completely hidden. I accepted the challenge and got to work! 👩‍🔧

We were provided with a reference image of the design, along with the required dimensions and the designated installation space.

1 Material & Tolerance Test

Before jumping into the design, I chose 12mm MDF as the material. To ensure a proper fit for the press-fit joints, I first milled a tolerance test. The result showed a kerf of 0.2mm, which I took into account throughout the entire design process.

2 3D Design — Autodesk Inventor

In Autodesk Inventor, I designed the structural components of the project: the back box pieces with their press-fit joints, the front board, and the grooves on the back of the board to house the LED strips.

3 2D Design — CorelDRAW

For the letters and their connections to the board, I worked in CorelDRAW. Since the CNC router also works with vectors — just like the laser cutter — I vectorized the logo and designed the joints between the letters and the board, as well as any additional adjustments the board required.

1 CAM — VCarve Pro

Before generating the toolpaths, the first step was to set up the job in VCarve Pro 7.5 ShopBot Edition by entering the material dimensions and depth — 2440 x 1520 x 12mm. Then I imported the pieces previously exported as DXF files from both Autodesk Inventor and CorelDRAW, and arranged them across the board to make the most of the material.

Once the pieces were placed, I checked for any open vectors before moving on. The next step was adding T-Bone fillets at the corners where the bit would struggle to reach. A CNC router uses a circular bit, which means it physically can't cut a perfectly sharp interior corner — it always leaves a radius. T-Bone fillets solve this by adding a small circular relief cut at each corner, allowing mating pieces to fit together properly without interference.

With the fillets in place, I generated the toolpaths. The order matters: pocket first, then internal cuts, then external cuts — this way the pieces stay secured to the sheet until the very last pass. Tabs were also added for extra security. For the second part, an additional pocket toolpath for the LED channels was included.

Part 1 — box pieces and board structure

• Pocket → 24 min 11 sec
• Internal profile → 1 min 7 sec
• External profile → 45 min 23 sec

Part 2 — main board with LED channels

• Pocket → 18 min 58 sec
• Internal profile → 3 min 55 sec
• Pocket — LED channels → 43 min 19 sec
• External profile → 16 min 17 sec

Part 3 — letters and logo

• Pocket → 3 min 41 sec
• Internal profile → 1 min 22 sec
• External profile → 13 min 31 sec

For the individual project, I used the 1/8" Straight End Mill (13728) for all toolpaths — a finer bit chosen to capture the level of detail in the letters and logo. Compared to the 1/4" Down-cut used in the group assignment, this bit required a lower feed rate to avoid breakage. The parameters used were the default values from VCarve Pro's tool database. Finally, VCarve Pro's 3D preview was used to verify everything looked correct before sending the files to the machine. The total estimated machining time for the entire project was 2 hours, 51 minutes, and 44 seconds.

To start, I turned on the machine and opened the ShopBot CNC software, which automatically prompted me to press the reset button to initialize the controller. Then I loaded the corresponding file for the first block.

To start, I turned on the machine and opened the ShopBot CNC software, which automatically prompted me to press the reset button to initialize the controller. Then I loaded the corresponding file for the first block.

1. Z-axis Calibration

Using the Z Zero Plate, a metal plate placed directly under the bit, connected via an alligator clip. The software automatically lowers the bit until it touches the plate, detecting the exact surface height. Once done, the software displays an alert reminding you to remove the alligator clip and put away the plate before continuing — a key safety step.

2. X and Y Axis Calibration

Setting the origin point for the horizontal plane, ensuring the machine knows exactly where to start cutting on the X and Y axes.

Once calibrated, I loaded the file and clicked Cut Part. The software then prompted me to turn on the spindle — on this machine, spindle control works through both the software and the machine itself: the software displays an alert, you press the physical Start button on the machine, and then confirm in the software — and the milling began.

Between each block, I took the opportunity to vacuum the sawdust generated during milling to prevent any buildup that could interfere with the next cuts. I also removed the pieces that were already loose, checking that each cut was clean — the tabs helped keep everything in place, so anything still well-secured stayed on the sheet. For the pieces that were harder to reach, I had to climb onto the machine bed to extract them — always with the machine off, of course.

Once all pieces were removed, each one was sanded individually to smooth out the edges and remove any excess material. After sanding, it was time to do a test assembly to verify that the tolerances were correct and that everything fit together properly and securely.

With all pieces sanded, it was time to assemble. The back box came together like a rectangular frame: the longer slats ran along the length of the board, and the shorter ones across the width. The joints fit smoothly into their corresponding slots — no forcing required, the press-fit worked exactly as designed.

The letters, each with their connectors, also fit perfectly into the cuts on the front board. One important design detail: the connectors had a deliberate height difference between the board and the letters, creating a gap that would allow light to escape around the contour of each letter once the LED strips were installed.

Since MDF tends to warp with humidity, once the sign was in its final installation position it was reinforced with wood glue for long-term safety — but during the dry assembly, the press-fits held everything together without any additional fasteners. The electrical work — painting, wiring, and installation — was handled by the infrastructure team, who collaborated on bringing the final piece to life.

The sign installed in its final location — off.

And just like that, the whole thing lights up! ✨ The LED strips bring each letter to life, illuminating the contours and the base of the sign.