Computer-controlled Cutting

The Coat of Arms of the Faroe Islands

I am from a tiny country in the North Atlantic Ocean called the Faroe Islands. If you draw a triangle between Iceland, Shetland and Norway, the Faroes lie in the middle of that triangle. For the vinyl project this week, I chose to make a vinyl version of the coat of arms for my laptop.

I found the image online, but although it was an svg file, it was not ready to be cut. The lines criss-crossed all over the design, and it would have been a terrible mess. I refined and simplified the image until I had two colors in individually distinguishable pieces that could be cut with ease. I cut them, peeled them and stuck one on the computer first, then the second. I drew squares to help me align the design, but it still wound up being slightly misaligned.

Editing and Refining

I used Inkscape to edit the svg file. As you can see, the original had many suporflous and criss-crossing lines. I used "path" - "simplify" (CTRL-L) to fix some of these issues, and used the "edit path by nodes" tool (F2) to manually delete and move any misbehaving nodes that remained.

Additionally, some of the shapes drawn up did not need to be there at all, so using the same tool, I selected them by clicking on them, then pressed "delete" on my keyboard to make them go away for good.

Origami and Sonobe units

Origami is the art of folding paper to create complex 3d shapes without cutting or tearing the paper. To me, it is an excellent aide in teaching 3d thinking, since it is at its core the art of transforming a plain 2d object into a 3d object. One of the most powerful origami patterns is that of the Sonobe unit. By combining multiple units one can create complex mathematical structures such as icosahedrons and dodecahedrons.

Last fall, I decided to attempt to recreate the Sonobe unit in wood using the laser cutter, press fit construction and living hinges. I drew it in Inkscape using the tabbed box maker extension While I created a functioning pattern this way, it has several drawbacks, one of which is that it is not parametric, so if I wanted a different size, I would have to start from scratch. I named these units Bunobe.

Parametric design in Fusion 360

I decided to continue working with Fusion 360 to recreate my Bunobe units as a parametric design, with adjustable material thickness, unit size and kerf. Initially I attempted to create the living hinge component as a parametric object as well, but repeated failures eventually convinced me that living hinges should be left as a fixed size that is constrained to align with a specific axis on the module. This also ensures a better functioning and more reliable hinge.

My first failed attempt was a mixup where I forgot to keep my construction lines in a separate sketch, so they transferred along with the shape. Additionally, the lines did not show on the 3D rendering.

The arrowhead hinge

This type of hinge has proven to be exceptionally flexible, but turned out to be rather difficult to draw. Each hole of the hinge has at least 14 lines, each line has several constraints telling it how to behave, each one was obeying 3 or for parametric measurements, and each time I made a parametric change the computer needed five minutes to compute the new drawing.

I learned a lot about constraints and anchor points during this exercise. As you can see, I had to redo them several times, since more often than not, a change in the parameters sent the shapes into new and unexpected configurations.

The oval hinge

Creating the oval hinge was an attempt to reduce the amount of lines and constraints required in the constructions.

This worked fairly well, but was ultimately abandoned because I realized that as the laser would draw the ovals, the material was highly likely to catch fire, since it would naturally draw an entire oval before moving on. With each line so close to the previous, once enough had been drawn to provide lots of airflow, it was a recipe for combustion more than anything else. I did test this design as a 3d drawing which was successful and gave me hope for the continuation of the project.

The (first) final design

Finally, I discovered that the hinges should be as simple as possible. I drew them up using the 3-point rectangle tool and mirroring them over the diagonal axes within the units. This time, redrawing the units from scratch took only about an hour, because of the experience I gained working my way through my failed attempts.

By this time, I have discovered the importance for a well structured layout, using sepperate components and sepperate sketches for each function. This way, I had one layer for guides, which consisted entirely of construction lines. On top, I had sketches for each type of unit, which I then extruded to the material thickness.

Further fine-tuning

Once I tried cutting the units above, the material caught fire. I knew it was a risk and I was ready so I could extinguish it immediately. The problem was that the lines were too close together, and the holes too large, which brings too much air in. Also, the material did not have time to cool down in between cuts. Knowing that I have a very good living hinge generator for Inkscape, I decided that the next version should skip the hinges in Fusion 360 altogether, instead adding them through Inkscape, where I will arrange the units for cutting anyway.

Even further fine-tuning

I decided to redraw the units because I discovered that these units do not fit together as well as I want them to. This is because I added the tabs onto the squares, rather than cutting the tabs into the squares. The difference is in the shape of the corners and the final size of the units. The new design works better, and is much simpler to edit parametricaly.

Ready to cut!

Here's the final version of the units, ready for cutting. I prepared two files, with the sides being 55 and 70 respectively, and added living hinges to them using the Inkscape extension mentioned above. The settings I used for the extension were in mm: cut length 20, gap length 2 and separation distance 1.6.