This week, we learned how to 3D print an impossible object using two methods: FDM and SLA. We also needed to maximize the size of our prints to optimize the available space in the gumball capsule we were given. This involved a lot of experimentation with sizing.
First, I chose the object I wanted to print. I used the template for a Flexible Cat found on Thingiverse. This qualifies as an impossible object because of the hinges/interlocking features found on the cat that allow it to move and bend.
I began by trying out the FDM printer at 100% scale. The print ended up having an extra support layer I had to tear off, and was too large. The next print I made I did at 70% and it turned out to be too small to optimize the space in the gumball capsule. The next four images show the cats that were too small and too large. I decided on a scale of 80% to fit the requirements of the assignment.
I printed out the right scale and the cat fit perfectly! It was just the right size to fit within the gumball capsule – any larger and it would not be able to close. I printed 4 of these cats with immense difficulty. Whenever I started a print and left before it finished, it got interrupted or stopped because I think people assumed it was a “fun” print. It was pretty unfortunate that I had to keep re-starting the process but I did end up with 4 identical and fully-articulated cats. I post-processed these by scraping and plucking off the excess filaments before sanding them down lightly to get smoother surfaces.
Next came the difficult part – SLA printing. The resin printer was never available when I was in the OEDK, which made it pretty tough to test out! But I printed out my cat successfully and washed it. However, the resin stuck together and sadly my cat was not able to be fully articulated in SLA printing. I followed all the steps that the TAs gave us – washing, blowing out excess resin with compress air, and then curing, but none of that worked. I was able to get one hinge of the interlocked part to move, but when I tried the other sections, my resin print very sadly and unfortunately snapped. It was tragic.
These pictures show my resin cat after being washed, and then after being air compressed and cured. Through this process, I understood the limitations of the SLA printer. As mentioned in the assignment, because my design has small tolerances and moving parts, the joints ended up fusing on the SLA machine, but are functional on the FDM machine. These are all my capsules loaded with cats. I also printed out pieces of paper with the user who uploaded the original CAD design and the link to the object.
Here is a picture of my clean workspace.
The total cost of my project is the following:
- PLA Filament: each of my cats used around 10g of filament, so total was around 50g. Scaling for a standard order of 1kg filament for $19.99 = $0.99
- Resin: FormLabs sells 5L of resin for $715. I think each cat probably used 5mL and I printed 2, so 10mL = $7.15
- 1 pack of sandpaper = $10.98
- Makerspace access for 7 days a week = $90/month
- Labor: 5 hours x 10/hr = $50
Total: $159.12
