Week 7: Computer-Controlled Machining

Group Assignment

What I Learned from the Group Assignment

From the group assignment I learned how to properly characterize and operate a CNC router. Before machining any design, it is important to understand the machine parameters and how they affect the cutting process.

One of the key concepts was understanding the relationship between spindle speed, feed rate, and chip load. These parameters determine how much material the tool removes and directly affect the quality of the cut, the temperature of the tool, and the overall machining performance.

Another important lesson was learning how to correctly set up the CNC machine. This includes fixing the material securely to the bed, choosing the appropriate cutting tool, setting the origin point, and verifying that the machine is properly aligned before starting the cut.

I also learned about an important design consideration when working with CNC routers. Since the cutting tool is circular, the machine cannot produce perfectly square internal corners. To solve this problem, it is necessary to add small circular reliefs in the internal corners of the joints, commonly called dogbone fillets. These allow the parts to fit together correctly during assembly.

Safety was also a critical part of the group work. CNC machines should never be left unattended while running, and it is important to use proper protective equipment. In our lab this includes wearing safety glasses and a lab coat, and it is also recommended to use noise-canceling headphones because the machine generates a significant amount of noise during operation.

Overall, the group assignment helped me understand that successful CNC machining depends not only on the design, but also on correctly configuring the machine, following safety procedures, and selecting the appropriate machining parameters.

Individual Assignment

Design Process

The first step was designing all the pieces in SolidWorks. I modeled every part individually and then created an assembly to verify that everything would fit together correctly.

To check this, I used the Interference Detection tool in SolidWorks. The path to this tool is:

Tools → Evaluate → Interference Detection

This tool allowed me to identify where parts were colliding or overlapping. After running the analysis, I made the necessary adjustments to ensure that all the pieces could fit together properly without interfering with each other.

When defining the joints, I used the thickness of the plywood board as my reference, which was 12 mm. Based on that measurement, I designed the slots and holes for the joints.

Preparing the Files for CNC

Once the design was finished, I exported the parts as DXF files so i could use them into VCarve to prepare the machining process.

In VCarve, the first step was configuring the dimensions of the material, including the width, height, and thickness of the plywood sheet.

After that, I imported all the pieces, the path is:

File → Import → Import Vectors / Bitmap

Then arranged them within the workspace. While positioning them, I made sure to leave enough space near the edges of the board so that the CNC clamps would not interfere with the cutting process.

Next, I selected each piece and used the Join Vectors tool to merge the lines that formed each shape. This step is important because it ensures that the CNC follows a continuous cutting path instead of stopping in the middle of the operation.

Toolpath Configuration

After preparing the vectors, I defined the machining operations.

First, I selected the vectors where I needed to remove a small amount of material so that certain parts could fit together properly during assembly. To achieve this, I used a pocket toolpath, which removes material inside a vector to a specific depth without cutting all the way through the material.

This pocket was necessary to create a small recessed area that allows the pieces to sit correctly when assembled. Without this step, the parts would collide and the joint would not fit properly.

Then I selected the vectors that needed to be cut completely through the material.

This is the final toolpath:

CNC Machining Process

Once the toolpaths were ready, I moved to the Asia Robotica CNC router to start the machining process.

Before starting the cut, I saved the file locally on the machine. This allows the cut to resume from the same point if the machine stops or pauses.

Next, I set the origin point by positioning the tool at the bottom-left corner of the material, making sure the tip of the bit was just touching the surface of the board.

The machine initially started cutting at 40% of the programmed speed, and I gradually increased it to around 90%. This must be done carefully because the wood chips generated during cutting can accumulate and heat up due to friction.

Post-Processing and Assembly

After the pieces were cut, I removed them from the board and prepared them for assembly.

Some joints required slight adjustments, so I used a Dremel tool to sand the edges until the parts fit properly. During assembly, I also used a rubber mallet to gently tap the pieces into place.

Once everything was adjusted, I assembled the structure.

Finally I performed some tests to verify that the furniture was stable and correctly aligned.

Final Result

Mistakes and How I Solved Them

Very Tight Joints

One of the main mistakes in the design was leaving the joints too tight. I designed the slots exactly at 12 mm, which was the nominal thickness of the plywood, without considering machining tolerances.

Because of this, the pieces did not fit together after cutting. To solve this issue, I manually sanded the joints using a Dremel until the pieces could fit properly.

Incorrect Cutting Depth

Another mistake occurred during the first toolpath configuration. I initially set the cutting depth to 12 mm, which was exactly the thickness of the plywood.

Because of this, the CNC did not completely cut through the material. To fix it, I changed the final cutting depth to 13 mm, allowing the tool to cut slightly into the sacrificial board and fully separate the pieces.

Recommendations

Use Tabs

It is highly recommended to add tabs when cutting pieces on a CNC router. Tabs are small bridges that keep the piece attached to the material while the machine is cutting.

I did not add tabs in my design. Fortunately nothing went wrong, but I saw others having problems when their pieces became loose during cutting. Tabs help prevent parts from moving, which could damage the tool or ruin the cut.

Leave Space for CNC Clamps

When arranging the parts in VCarve, it is important to leave enough space near the edges of the material to avoid interfering with the clamps that hold the board in place.

Downloadable Files