This assignment challenged us to create an “impossible” object that can only be created easily by 3D printing. I came across the Mobius Doughnut, designed by the user Tzani, while digging into Thingiverse for cool and uncommon interlocked objects. While there were dozens of interesting objects that caught my attention, this object stood out because it looks like two interlocked rings at first but becomes a perfect doughnut when rotated correctly. In addition, I experimented with this object first and failed, which motivated me to push through and get it right. As I have the most experience with FDM(Fused Deposition Modeling) printing, I started working with FDM printers first.

Above are pictures of my first attempt with a Prusa MINI. Despite the geometry of the object suggested it would require supports, I chose to start with a Prusa MINI because I wanted to get an idea of how big the object will turn out to be, and I was also curious how single-extruder printers generate supports. Once I got the print back, I quickly realized what improvements I could make. The size of the object (10mm x 12mm x 7.5mm) was very small compared to the gumball, and there was too much support that I was unable to break them off of the doughnut as desired. This prompted me to scale the object up by 400% and use a dual-extruder printer for the next step.

I chose to experiment with the Ultimaker 3 next. I had high expectations for Ultimaker 3 because it is equipped with two extruders and a different support material, which would address the problem of detaching supports from the print. However, my prints failed time after time due to different reasons. On my first try, the job had to be aborted quite early when the support structure collapsed. On my second iteration, the extruder got clogged at the beginning and didn’t deposit support material correctly. On the third trial, the support structure collapsed again, further into the print. Below are some pictures of failed prints on the Ultimaker 3.

Upon discussing the issue with Fernando Cruz, I was encouraged to try out the brand new printer at the OEDK: the MakerBot. The MakerBot was able to produce exactly what I wanted from the Ultimaker 3. Since the supports are soluble, I used the bath in the wet lab to remove all supports. I didn’t get any pictures of the object straight out of the MakerBot as Fernando moved it to the bath for me, but below is a successful FDM print of the Mobius Doughnut!

I planned to replicate this process for more models, but the MakerBot broke down shortly after my successful print, which forced me to look into single-extruder printers again. Using the Prusa i3 MK3, I was able to obtain an object similar to my very first experiment but scaled up by a factor of 4. Even though this model also had a lot of support, I was able to use a knife to break the support off manually as it was much larger. In this process, there was minor damage done to the print and the bottom of one of the prints got pulled off with the support as shown in the picture below.

The second 3D printing method I used was SLA(Stereolithography) printing. While the Formlab printers used a different slicing software, it was similar enough for me to navigate through it. The first trial failed at first when the mixer fell out of place, but the second iteration generated a high-definition print, which surprised me. The only downside to this print was that I had to snap off the supports manually, and it left marks or bumps on the surface of the print which I had to sand down.

Cost Analysis

In conclusion, I was able to obtain 3 FDM prints and 2 SLA prints of the Mobius doughnut through multiple iterations.

FDM (1 print, MakerBot)

*** The slicer is currently not allowing me to access the print information as the printer is out of order. Once it is fixed, I can update this!

FDM (2 prints, Prusa i3 MK3)

Print time: 3hr 29min

Material: PLA, 22.28g

Cost: $0.45

SLA (2 prints, Form 3)

Print time: 3hr 19min

Material: Grey pro resin, 27.24mL ($175/1000 mL)

Cost: $4.77