Assignment #3
Computer-controlled cutting
The third Fab Academy assignment is computer-controlled cutting. Unlike the previous assignment, it does not yet have a direct application in my final project, so I designed exercises to test and improve my cutting skills.
1 – Vinyl Cutter
The first machine I’m going to experiment with is the vinyl cutter, a very powerful machine that allows you to cut many materials… To work with this machine I thought about cutting a graphic to transfer on my computer... As you might have seen on my previous assignment I’m really into open-source software, and therefore I’m going to make for myself a KiCad sticker, inspired by a graphic used to promote an event called “the state of KiCad”.
I imported an image downloaded from the KiCad website. I tried using “Trace Bitmap” to convert it into vectors, but the results were not satisfactory.
Instead, I drew the logo elements manually using Bézier curves. I adjusted the stroke widths and used “Stroke to Path” to turn them into closed shapes. Finally, I combined the elements with Boolean operations to create a single cutting graphic.
To drive the Crunchlab’s Cameo 3 I used Inkscape with the plugin Inkscape-Silhouette, it is possible to install it via terminal following
this tutorial.
Once the drivers and the plugin were ready it was time to play with the machine.
To get an overview about the machine I carefully watched this other tutorial.
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I placed the vinyl on the supplied cutting mat and loaded it into the machine. Then I opened the Inkscape-Silhouette plugin settings.
The plugin lets you set the cutting speed and force and includes presets for materials such as vinyl. I set both the force and speed to 10.
So I clicked on “apply” and the machine started moving, producing the graphic I wanted on my piece of vinyl.
The speed and force settings worked, but the generated cutting job left about 85 mm of empty space above the graphic. Adjusting the plotter settings did not fix it.
In the end, I moved the vinyl down slightly, which solved the problem. This issue did not occur when I tested the machine with its official software.
Cutting went well, but peeling away the unwanted vinyl was more difficult, probably because the logo had some intricate details. After one failed sticker, I sent the job again, and the second attempt succeeded:
Now like any other extremist I’ve got my symbol to venerate and show around...
2 – Laser cutting
Next, I worked with the laser cutter at Crunchlab. I designed test shapes to explore the cutting settings, the material’s flexibility, and the joint tolerances needed for a construction kit.
I used FreeCAD and Inkscape again. In FreeCAD, I linked parametric sketches to a spreadsheet containing the dimensions I wanted to test. I modelled simple pieces with slots, using the spreadsheet values as constraints. Then I exported 2D drawings through the Draw workbench and added bending patterns in Inkscape.
I found online here an old DXF/AI file containing several bending patterns. I imported these into my test design. An SVG version is available at the bottom of this page.
At this point I was quite happy with my test file, and I finally started to work with the machine!
I prepared the first cutting job in the laser cutter’s software, using the test shapes and a series of squares. I adjusted the power, initially between 0 and 90%, and the speed in millimetres per second. Crunchlab keeps a record of previous cuts, which helped me choose starting settings. I also experimented with the values, then exported the cutting files to a USB drive. At the machine, I placed the wood on the bed, focused the lens on its top surface, loaded the files, checked the material’s position, and started the cut.
Afterwards, I examined the results. Some squares had not cut all the way through, and the kerf widths varied with the settings. Of the bending patterns, the cross-shaped one was the most flexible. The joints were more challenging: even the smallest slot produced a loose fit.
I first tried increasing the cutting speed, but the joints were still too loose. I then returned to FreeCAD and reduced the slot dimensions in the spreadsheet. The next cut finally produced a good fit.
The settings that worked for these pieces were 95% power and a speed of 60 mm/s. The software lets you assign colours to paths and set different speeds and power levels for each colour.
Next, I designed the construction kit requested by Neil. It would consist of cross-shaped pieces with flexible arms and connectors that could form different shapes.
In FreeCAD, I designed a cross-shaped piece and a connector, using a spreadsheet to control their dimensions based on the earlier tests. I exported the model as an SVG and added the bending patterns in Inkscape.
I returned to the cutting software and prepared the machine files. Using 95% power and a speed of 60 mm/s again, the cut went smoothly, and I finally had the pieces for my construction kit.
3 – Assembly
The last step was assembly. Although I had tested the joints and bending patterns, I was still nervous about breaking the pieces. Fortunately, they fitted together and stayed in place. I only had time to make two pieces, but more could be produced and combined in different configurations.
And that’s it, the kit works well and everything stays in place…
4 – Source files
Here are all the source files for the Computer-controlled cutting assignment:
1 – vinyl cutter vectors
2 – laser test parametric 3D model
3 – laser test vectors
4 – bending patterns vectors
5 – construction kit parametric 3D model
6 – construction kit vectors
5 – Notes, takeaways, and plans for the future
I enjoyed this assignment and would like to explore several aspects further. First, I want to understand the extra space introduced by the Inkscape cutting plugin. I’d also like to try engraving graphics on my designs and make more construction kit pieces for larger configurations.