In week 7, the focus was on large-scale digital fabrication using the CNC router (Computer Numerical Control router). Unlike smaller digital fabrication tools such as laser cutter or vinyl cutter, the CNC router allows the fabrication of large structural objects from sheet materials like plywood or MDF of greater thickness.
Before designing for CNC machining, it’s important to understand some key concepts that influence both design and fabrication process. For this, I consulted our Group Assignment.
When working with a CNC router, it’s important to follow basic safety guidelines to prevent accidents and ensure a proper machine operation.
For this project, I designed a rocking chair for young children with soft organic shapes. The design focuses on simplicity and CNC fabrication, using press-fit joints to assemble the structure without glue or additional fasteners.
Onshape is a cloud-based CAD software used to create and model the 2D and 3D design of the rocking chair before preparing it for CNC fabrication.
The design process started by creating a 2D sketch of the side profile of the rocking chair in Onshape. This sketch defines the main shape of the rocker base, the backrest angle of 30º, and the 12 mm thick slots used for the press-fit joints.
All the spaces for fitting pieces were 12 mm thick, as that corresponded to the plywood board I will be using.
Next, the geometry of the rocking base was defined using 2 large ovals. The dimensions were added to control the radius and length of the rocker, to ensure a stable rocking motion and proper balance of the chair.
After defining the geometry of the rocking chair, the chair's dimensions were refined to adjust the design's proportions. Tangent lines were added to connect the shapes and the intersections of the ovals were eliminated.
Then three more intersecting ovals were placed to create an organic perforation in the profile of the chair and these were joined with tangent lines to close the geometry.
Finally, when the desired shape was obtained, the Trim tool was used to remove the extra lines.
A separate sketch was created to design the backrest panel of the chair. The piece was defined as a rectangular shape of 650 mm wide and 300 mm long, with rounded corners of 30 mm radius to improve comfort and avoid sharp edges.
Another sketch was created to model the seat of the chair. The shape was defined as a rectangular surface of 650 mm wide and 450 mm high with rounded corners of 30 mm radius, and slots of 126 mm long were added to allow the side panels to fit into the seat structure during assembly.
After finishing the molding of the parts, I used a new Part Studio to create a rectangle measuring 1220 mm by 2440 mm, which are the dimensions of the plywood sheet. This will help to fit the parts into the material and make better use of it. Finally we export it in a DXF file.
VCarve is a CAM software used to prepare designs for CNC machining. It allows importing vectors, creating toolpaths, and defining cutting parameters before exporting the file for the CNC machine.
When opening VCarve, the first step is to Create a New File. This will open the Job Setup window, where the material dimensions will be defined.
In this section, we enter the dimensions of the wood sheet that we will be using. Once all the values are entered, click OK.
For this go to: File → Import → Select your DXF File → Open File
After importing the design, it has to be positioned inside the material boundaries. The pieces can be moved, ratted or duplicated if necessary with the tools on the left side. Also here can be added the dogbone to the internal corners where parts need to fit together.
Select the vectors to cut and choose Create Profile Toolpath. In Tool, we click on Select → Metric Tools → End Mills → Configure the Diameter of the mill → OK.
In Cutting Depths we configure the Cut Depth (C) which should be slightly deeper than the material thickness to ensure the pieces are fully cut through.
In Machine Vectors we can choose if the CNC can be cut inside, outside or on the vector line, depending on the desired final dimensions of the part. In my case, I used the outside cut for the outer contour of the pieces, and inside cuts for the slots. Nevertheless, to configure an internal and an external cut, they must be created in different VCarve files.
Once all the parameters are defined, click Calculate Toolpath. VCarve will generate the cutting path for the CNC machine.
After calculating the toolpath, we save it by doing click on Save Toolpath(s) to File, but first we select the Post Processor, in my case a choose the Mach2/3 ATC Arcs (mm) (*.txt), since this is the program that I will be using to control the CNC.
Mach3 is a control software used to operate CNC machines. It loads the G-code generated from CAM software and controls the movement of the machine during the machining process.
First the CNC machine and the control computer must be turned on.
Once the wood sheet is placed on the CNC bed, it needs to be secured using nails to prevent any movement during the cutting. I put nails in the warped parts of the board.
First, open the Mach3 CNC software on the computer connected to the machine.
Click on Open → select the file exported from VCarve. Once loaded, Mach3 will display the toolpath preview of the design.
Using the jog controls in the keyboard, move the spindle to position the tool above the desired starting point on the material. For this I positioned it above the lower left corner of the board.
In the software, set the X, Y and Z in zero positions by clicking in the yellow icons of each axis. This defines the reference point from which the machine will start cutting.
Before starting the cutting process, we set the spindle speed to 18000 revolutions and then turn on the spindle so the cutting tool begins rotating.
Press the green button to Start to begin the machining operation. The CNC will follow the toolpath defined in the G-Code of our file. During this process it is important to continuously monitor the machine.
Once the job is finished, the spindle will come back to its original position. After this it is important to move the spindle to a safe position and turn off the machine before removing the material.
After removing the cut pieces, we removed the nails from the material with a hammer and removed the material. Using a vacuum cleaner, we began to remove the dust generated during cutting.
To improve the surface finish, the flat areas of the pieces were sanded using an orbital sander, removing small imperfections left after the cut. Once sanded, the chair was assembled using press-fit joints, allowing the pieces to interlock and form a stable structure without glue or additional fasteners.
Working with the CNC machine was a challenging but very rewarding experience at the same time. Learning how to prepare the design, generate the toolpaths, configurate a big machine, calculate the right parameters and fabricate the parts required careful planning, but I really enjoyed the process since I could get to know hoy to operate correctly the CNC router. In the future, I would like to further develop this project and build my rocking chair at a larger scale.
In this section, you can find the downloadable source files developed during this week.