Ever since I got my 3D printer, I have been wondering whether it was possible to produce transparent parts. While there are plenty of transparent filaments sold on the market, they typically do not produce transparent prints, but rather translucent ones.
The difference between transparency and translucency is in the material’s tendency to diffuse light. Diffusion may result from several factors, the most dominant one in our case is the inhomogeneity of the print. Under normal settings, the printer leaves small cavities (bubbles) inside the print. Each cavity acts as a small lens (as it is curved) and scatters the light passing through, obscuring any image standing behind the print and making it… translucent!
Having in mind that the plastic itself is inherently transparent and that bubbles from the printing process are the only thing preventing us from achieving optically clear prints, I began searching for the right print setting to accomplish the task.
I started by searching the internet for prior attempts, but all I could find was this YouTube video. It was a great start, but I wanted to achieve clearer results.
In short, the basic settings using CURA are:
- Layer Height: 0.05 mm
- Infill Density: 100%
- Infill overlap percentage: 6%
- Flow: 108%
- Print Speed: 24 mm/s
- Enable Print Cooling: OFF
- Printing Temperature: 255 °C (on the highest end of the recommended range, I was using prusa’s ABS)
- Build Plate Temperature: 100 °C
- Nozzle Diameter: 0.4mm
The main purpose of the setting above is to make the laid plastic’s consistency as thin as possible by heating it to the highest possible temperature, and then forcing it into the grooves of the previous layer by applying over-extrusion (flow > 100%).
(I found it especially difficult to eliminate bubbles at the interface between the infill and the outer wall. To deal with this I changed the infill overlap).
Before printing, make sure that the hotend is clean, as leftover material in the part can damage its purity. After the first layer has been laid down, the hotend must be as close to the build plate as possible, but not too close as it might get clogged or even scratch the build plate. To find the sweet spot, I found it best to adjust the “live Z” (on prusa MK3/2) to the point where the air gap between the tip of the hotend and the build plate just disappears. This rule of thumb ensures that the plastic is forced into any gaps between the first layer lines and the build plate.
The down-side of over-extrusion can be seen in the video below, in which a “plano-convex spherical lens” (flat on one side, and curved on the other) is being printed. Notice that the hotend is scraping the last layer, and is pushing on a chunk of excess material resulting from over-extrusion. The chunk is more pronounced on the first layers and typically ends up on the surface of the model. Worry not, as it can be easily removed with a crafting knife.
The next step is to turn the rough surface into a smooth one. In my first attempt I used acetone smoothing, and indeed, the surface got a lot smoother, but it also made the part look undesirably foggy.
Another technique I’ve tried and found successful was dry sanding using sandpapers raging from 600 grit to 4000, incrementally. It’s worth noting that cardboard can also be used instead of a high grit polishing paper.
The reason why I’ve made all of my lenses flat-bottomed is that printing curved shapes would require hard-to-remove supports. Additionally, while sanding a flat surface can be done easily on a flat platform, such as a table, there is no easy way to smooth a curved surface, and hand-sanding it can distort its geometry.
Although the quality of these lenses is not good enough for imaging (e.g. for the use of cameras), they’re certainly capable of focusing light!
So Let’s Have Some Fun!
And nothing says fun more than LASERS! (pew pew pew) I’ve made a plano-convex cylindrical lens and a mount for holding the lasers parallel to each other. You can see how the laser beams are all focused into one spot. Success!
Another neat idea I had was to try and make something similar to those glass blocks that are laser-engraved with 3D figures. I downloaded a model of my favorite character – Mario. Using Blender I placed the model inside a cube and used the tool ‘Boolean’ to produce a cavity with the figure of Mario inside the cube. The result was not perfect, but I find it pleasing and unique.
One thing to note is that slicing softwares don’t like internal cavities. They see floating spaces as an error and try to correct them automatically. In order to “convince” the software to leave my shape alone I had to connect at least a small part of it to the outer shell. With the Mario figure, I simply moved it down so the shoes will touch the bottom part of the cube. I couldn’t find any option in Cura or Slic3r to disable error correction, and would love to find a way to allow internal cavities.
Looking for something more complex to make, I found this little thing and printed it using the process described above (this time I was a bit lazy with the polishing).
Below are some more examples: the prism on the right produces a small rainbow and the big lens can focus sunlight from one side of the room to the other. The bottom right print is just a simple round window that turned out almost perfect, because, as I mentioned before, flat surfaces are the easiest to sand.
And last but not least: a Fennec fox ring