The main idea here was for me to improve my laser cutting skills. But I reallllly wanted to make some art. Normally I like to combine engineering and art into one project, but for this it made sense to separate the two somewhat. I decided to make some artwork out of cardboard, but I saved the more in depth engineering for a partially optimized double "mortise and tenon" snap lock joint. The goal was to make it work for 3mm plexiglas first, and then hopefully develop some design rules that can be applied parametrically in either SolidWorks or Rhino/grasshopper.

Above is the final result of the "dark box" with negative space image. To be clear, this is not a stencil or a vinyl cut. This differs from a stencil in that the negative space automatically creates what appears to be a shadow when a dark background is used. The box was created with some very simple laser cut cardboard pieces. I suppose the cutouts could have easily been designed in Adobe Illustrator or Corel Draw, but I did them in SolidWorks which is just as easy and can update parametrically should chose to tweak the design. The image was created using a photo of my girlfriend, Kara Henderson, which was then edited in Adobe Photoshop and Illustrator.

I made several attempts at the image cut before I made the full box to make sure that it came out the way I wanted. It was a bit tricky to get the focus just right because the cardboard was a bit warped. Ultimately, I found that by cleaning the laser cutter mirror and lens and by forcing the autofocus on the top left corner I could get a better cut. I also turned up the power to about 40 and turned down the speed to 38. I also used a frequency of around 450. This ensured the cut went the full way through regardless of the warpage in the cardboard. Of course these settings are very dependent on how warped the material is, how thick it is, and the quality of the Epilog lens.

This image shows a snapshot of the DXF file that was cut on the Epilog laser cutter. The photograph was taken on an android phone after which it was processed in Adobe Photoshop. The "Adustments -> Threshold" tool was used to take the image and turn it into a black and white. I had to apply the threshold tool to local areas because some areas were darker than others. I'm not showing the original image because it's private!

This is what the raster (or bitmap) image looked like before I converted it to a vector image in Adobe Illustrator. This file was manipulated in Photoshop so that there were no large "black" portions that would make it impossible to stay together. I broke up the larges sections by running thin "positive space" lines through them. I also made sure there were no isolated positive spaces (that would just fall out after laser cutting). Isolated negative spaces are ok of course.

By using the "Object-> Image Trace-> Make" command in Adobe Illustrator I was able to convert from raster to vector. Keep in mind this vector format is "filled in", so you have to select the image and change it to "no fill".

Nothing interesting to see here… just the cutouts for the cardboard "kit" box. Really easy to do in pretty much any graphics or CAD program. I chose SolidWorks since everything updates parametrically when I made changes. At first I made the "tabs" a bit too small for example. But by simply chaining one dimension they all updated.

The cardboard laser cutting was fun, and it's a super cheap material to make artwork with, but it's difficult to get the precision required for more complicated stuff that could otherwise be achieved with plastics. I took some plexiglas and started messing around with different kinds of connectors. The image above shows the iterations on a double "mortise and tenon" snap lock joint. The first attempt is in the lower left corner and the last attempt is in the upper top corner.

These two images show the basic geometry.

This image shows how a closed snap join can clip into another snap joint. I didn't bother to laser cut this one, but it might be fun to have multiple elements in my kit.

Here I used SolidWorks Simulation to make sure that the flex clips could handle the stress (and provide enough force) when clipping the tenons into the mortise holes.