Week 7
Computer-Controlled Machining
Week assignments
- Group assignment
- do your lab’s safety training. ✔
- test runout, alignment, fixturing, speeds, feeds, materials, and toolpaths for your machine. ✔
- Individual assignment
- make (design+mill+assemble) something big (~meter-scale). ✔
- extra credit: don’t use fasteners or glue. ✔
- extra credit: include curved surfaces.
Group Assignment
I think the CNC is my favorite machine in the Fab Lab, though the robotic arm has been gaining a lot of points in the last few months. Pablo and Francisco had never used the machine before, so as part of my work at the Fab for years, I’ve been sharing the instructions for safe use and how the machine works.
On Thursday, March 6, I showed them how to use the machine safely. I explained the importance of wearing gloves, protective glasses, and also headphones to protect their ears from the noise the machine makes when milling materials like wood.
I also taught them the basics of how VCarve Pro works, and we designed a small piece with a drilled hole, engraved text, an inside cut, and an outside cut. We used a drill bit, a V-bit, and a 6mm straight end mill. This way, we could practice the initial warm-up process of the machine, tool placement, setting the origin for the job, and calibrating the Z0 height. We repeated the process several times until everything was perfectly clear for everyone.
Before making something big, we first prepared small samples to find the optimal allowance offset. This way, the components in our design could fit together without needing screws or glue. I created three toolpaths with different offset values to test which one worked best after milling the pieces. I also explained how to generate different types of fillets to ensure the components fit together properly.
Link to week 7 group assignment
Individual Assignment
I’ve had a couple of ideas in mind for a while about building something big. One of them was making one of the beam supports for my final project, but right now, I think I can improve the design and optimize its final shape. That’s why I decided to build something I believe we need at the Fablab ETSAC Coruña—a standing worktable.
As you can see in the picture, the main space in the Fab Lab has two freestanding pillars, and that’s where I want to place the table.
After sketching out some basic ideas, the table started to take shape. The following screenshots show the first design proposal.
The perimeter of the two pillars forms a rectangle of 800 x 400 mm. Using leftover wood from the Fab Lab, I’ve put together a basic design that can be adjusted as needed before fabrication and assembly. My plan is to make it so it can be assembled without glue or screws, except for the top surface, which will be secured with hidden fasteners to the lower tabletop for extra rigidity and stability.
The 3D design and its XY 2D projection were generated using key parameters like table height, board thickness, and the overhang of the supporting elements. The crossbars will be locked in place with wooden wedges to secure the table to the perimeter of the support structure.
I started designing on Thursday night. On Friday morning, I had class at school, so I couldn’t work on it until the afternoon. Right now, it’s 8:11 PM, and the design is finished. I just need to carefully review it tonight, and tomorrow I’ll be able to set up the toolpaths in VCarve and start fabrication.
This afternoon, I also took inventory of leftover MDF boards, phenolic plywood, and particleboard. My plan is to use scraps from other projects to build the table components. The inventory is also essential to determine the cut list for both the upper and lower tabletops.
Due to the size of the available boards, I designed the table with two uses in mind. One of the uses is as a standing worktable with a riser in the lower section and when this riser is removed, the table can also be used as a traditional seated one.
CNC Machining Process for Table Construction
Initial Setup and Toolpath Preparation
Once the base geometry was defined from the 3D model, I imported the vectors into VcarvePro 8.5 and began preparing the toolpaths for each of the tasks. I made sure to chamfer the interior corners to allow for proper assembly of the different parts. These chamfers are directly related to the tool selected for cutting the boards—in this case, a 6mm straight end mill.
The image below shows the end mill I used, along with the rotation speed, movement speed, and plunge rate values.
These values are indicative. Fine adjustments are typically made at the start of the machining process. For me, the noise generated during cutting is the key indicator of whether I can increase or decrease the speed or adjust the rotation of the end mill.
Fabrication of the Crossbars
The first pieces I fabricated on the morning of Saturday, March 8th were the top crossbars that will support the tabletop.
Compared to the initial design, I modified the crossbars to reduce their section after the support area, achieving a lighter visual appearance.
Testing and Error Detection
Next, to detect potential errors, I cut the board with the lower extension of the table. This step was crucial to verify that the dimensions matched reality and to ensure I wouldn’t waste material before generating all the pieces.
At this point, reality came knocking. While placing the pieces around the pillars, I detected a beginner’s mistake—one that, as an architect, I’m somewhat embarrassed to admit. When I noted the dimensions of the pillar contours, they were 800x400 mm. While generating the toolpaths, I accounted for a 0.5 mm tolerance, but I failed to consider the dimensional changes in the base of one of the pillars. Due to construction errors in the building’s formwork, one of the pillars has a thickening at its base, requiring an additional 10 mm for the lower support pieces to fit properly. Fortunately, I caught this mistake in time.
Perhaps I should have 3D scanned the pillars to obtain an accurate 3D model.
Material Constraints and Adjustments
As mentioned earlier, I’m using leftover boards from other projects to build the table, which adds an extra layer of complexity. I had to adjust the sizes to match the available material in the fab. For my final project, I’ll ensure that the necessary materials are ready weeks in advance.
Weekend Progress
Saturday’s work went pretty well—got a lot done. I took the afternoon off to hit the cinema and catch The Brutalist. On Sunday, I got the cutting paths ready for the rest of the pieces, so I can cut them on Monday in the fab.
I’m also figuring out how to connect the boards for the tabletop and thinking about adding some kind of engraving as a cool little reminder of this project.
Assembly
On Monday, I had to wake up early, and by 7:00 AM, I was already cutting the pieces I needed for the table support structure. In the picture, you can see the parts prepared for assembly. I had to make some minor manual adjustments to adapt to the irregularities of the support structure mentioned earlier.
Pre-assembly
Overall, the parts fit quite well. The offset adjustment to -0.25 mm in VCarve Pro turned out to be perfect.
Before tightening the wedges, I performed one last check to level the base of the workboards.
With the structure assembled and leveled, I was able to cut the pieces that make up the lower tabletop. I used 12mm thick MDF laminated boards.
I divided the tabletop surface into four sections joined together using these wooden connectors.
In the picture, you can see the assembly of the table top on the table structure.
For the upper tabletop, I needed adjust the inner boundary to the irregularities of the two concrete pillars. To do it properly this time, I scanned the area using my mobile phone with the Scaniverse app.
I exported the scan in .obj format and imported it into Rhinoceros, positioning the mesh centered at the origin and aligned with the XY plane.
I defined a flat mesh to find the intersection between both, obtaining a polyline with the actual shape of the supports at that level. I will apply a 5 mm tolerance to this curve to generate the inner contour of the workboards.
I’m really happy with how the connection elements between the parts of the table top turned out with such amazing precision!
On Wednesday, March 12th, at 11:00 AM, the table is already set up, and the ETSAC students are acting as Beta users. So far, their feedback has been really positive. In a few days, I’ll need to apply a protective lasur and add a veneered top layer to make the work surface more durable than the MDF I initially used.
FabAcademy works!!
Final Thoughts & Lessons Learned
Working with the CNC milling machine comes with some risks when handling it. I’ve been trying to explain to my teammates, Pablo and Francisco, how important it is to use protective gear—gloves, safety glasses, and ear protection—to work as safely as possible.
The ability to create models and the variety of tools available for different tasks make this machine incredibly versatile. This week’s assignment gave me the chance to fine-tune the tolerances between the connection and anchoring elements of the table components.
Next week, we’re moving to a smaller scale, and we’ll need to apply everything we’ve learned so far to successfully mill the PCB.
Files week 7
Test plots for group task. Vcarve 8.5
Standing Worktable. Vcarve 8.5
Standing Worktable. Rhinoceros 8. Zip
Pillar intersection with Mes Plane. Grasshopper
Free download from SketchFab: