For this project, we were tasked with 3D printing an impossible object – something that theoretically cannot be created with a method other than 3D printing. I started by looking at previous blog posts for what is considered “impossible” and liked the “Flexi-Rex” object several people had posted about before. These objects are considered “impossible” because they have interlocking body sections that allow it to move.

I went to Thingiverse and searched for “flexi” to find similar animal designs, then selected this elephant. From there, I realized you can pick “remixes” to find files of modifications other people have made to the original file. I picked this one, which had a hole to make this flexi-elephant into a key chain.

FDM Process

I downloaded the .stl file onto 3DprinterOS to prepare and slice objects to be 3D printed on the Prusa i3 MK3. After I uploaded it, I centered it and put it on the bed. I used calipers to measure the outside diameter of the gumball container to be about 50mm. Based on this, I adjusted the size of my elephant to be 44mm wide so that it would fit standing in the container. I went with the recommended settings from Thingiverse of 0.1 mm layer height and no supports and kept the OEDK default settings of 1 mm wall thickness, 15% infill density, and 215 degrees Celsius printing temperature. For this iteration, I did not adjust the build plate adhesion type because I did not notice that option and did not review the OEDK printer guide beforehand. So, my first 3 prints printed with a raft. Ultimately, the raft was way too strong for my short print and I was unable to remove it from the back of the prints.

 

To adjust this, I printed the next 3 elephants with a brim instead of a raft and made the layer height 0.2mm instead to make the print run faster. Overall, the quality difference between the layer heights was not noticeable, the brim was easy to remove, and they printed much faster!

SLA Process

For the other two elephants, I used the Form 3 printer with Grey Pro Resin. Since I have more previous experience with the SLA printers, I think this process was more seamless for me. I printed these two elephants with a slight angle in the supports and they came out nicely the first time. Luckily, the supports did not bond the interlocking parts together and the elephants can still articulate.

In conclusion, I am happy to say that I ended up with five successful prints! Next time, I will definitely double check the plate adhesion settings to avoid unnecessary time spent on the printer to speed up production.

Cost Analysis:

• Labor – I spent about 30 minutes identifying a part to print, modifying the file in 3DPrinterOS’s slicer, and about 1 hour setting up prints and waiting at the OEDK. With an hourly rate of $20/hr, the total labor time was $30. I assume the hourly rate per my time also accounts for part of the machine time.
• SLA Prints – I printed 2 elephants on the Form 3 with the Grey Pro Resin. In total, the print took ~2.25 hours to print and 17.21mL of material. At $175/L of resin, the approximate cost for this print was about $3. Then, the prints took about 30 minutes to wash and cure.
• FDM Prints – In total, I printed 6 elephants on the Prusas. The first 3 that did not come out as planned cost $0.33 for 16.11g and took about 4 hours and 11 minutes to print according to 3DPrinterOS. The 2nd 3 elephants that worked properly cost $0.27 for 13.62g and took about 1.75 hours to print.
• The initial cost of the Form 3, its associated wash and cure machines, and the Prusa were not included in this calculation.
• The total cost of the project was $33.61.