Assignment #7
Computer-controlled machining

The seventh Fab Academy assignment is computer-controlled machining. We have to design and build “something big” using a large CNC milling machine.

1 – A plant holder

Fab Labs can be full of fumes and dust from laser cutting, milling, and soldering. This inspired me to make a holder for a plant, bringing some greenery into the workspace. The holder will have three legs joined by two rings. The pot will sit in the centre and help keep the legs pressed against the rings, making it part of the structure.

2 – Parametric 3D modeling in FreeCAD

I began by creating a spreadsheet of the dimensions for my 3D model. In FreeCAD’s Part Design workbench, I used Sketch and Pad to make the first leg and the rings. Finally, I used a circular array to create three legs.

3 – CAM

Once I was happy with the design, I arranged the parts on the XY plane using the Draft workbench and switched to the Path workbench. Path generates toolpaths around the shapes and exports G-code for the CNC machine. First, I created a “Job” and specified the dimensions of the wooden stock. Next, I added the cutting tool to the tool library: a flat 3 mm bit. I also set the feed and jog parameters in the “Data” panel on the left. I generated a contour path for the outer edges and an edge-based profile for the inside of the rings. I then added dogbone reliefs at the joints and tabs to keep the parts in place during milling, using the “Path dressup” menu. Finally, I exported the job with the LinuxCNC post-processor, which is compatible with UCCNC, the software used to control the machine. The setup used a flat, two-flute 3 mm bit, a feed of 30 mm/s, a 3 mm stepover, and a spindle speed of 10,000. The spindle speed is set manually with a knob on the spindle. Before moving to the actual machine I used the simulation function of the software, so that I could double check if all the settings were correct.

cam_simulation_plant_holder from Chi Ha Ucciso Il Conte on Vimeo.

3 – CAM for final project

Alongside Neil’s furniture assignment, I decided to mill a part for my MIDI controller. I returned to its CAD model and followed the same process to generate toolpaths for the circular wooden handle.

Screencast 2020-03-14 010104 from Chi Ha Ucciso Il Conte on Vimeo.

4 - Cutting my pieces

Lab access was limited during the COVID-19 pandemic, but I eventually had a few hours to complete the CNC work. I used a Stepcraft 2/840. I attached the wood to the sacrificial layer, set the origin in UCCNC, and started the cut. The job went smoothly. Afterwards, I removed the parts and sanded their edges.

5 - Assembly

The final step was to assemble the plant holder.
I designed the connections to fit perfectly, and the result was as expected:
The parts are easy enough to put together and they stay in place firmly. On top of that, the vase prevents the legs of the holder from moving backwards, and the piece is therefore very steady.
I'm really happy with how this assignment went.

6 – Milling final project wooden element

After my plant holder, I went for the wooden element of my final project.
The circular handle for my final project will be milled from a piece of fir wood.
As before, I set the milling origin and sent the job to the machine. I then removed the tabs with a Proxxon and smoothed the piece with sandpaper.

7 – Assembly test for the wooden element

The printed shells fitted the wooden element perfectly. Once secured with screws, the assembly was firm and stable. I really like the combination of black plastic and wood. I may stain the wood before applying a protective finish.

Source files

Here are all the source files for the computer-controlled machining assignment:
1 – Plant holder 3D model
2 – Plant holder CAM
3 - Final project CAM