This week’s assignment was to create an impossible object (an object that can’t be created if not for 3D printing) using two different 3D printing methods. When searching for my object I simply typed in “fun objects” on Thingiverse and stumbled across this slug, which I decided to print. This design satisfies the impossible criteria with its interlocking body sections, which allow it to articulate.

I started by downloading the .stl file onto 3DprinterOS, which is the software the OEDK uses when to prepare and slice objects to be 3D printed. After I uploaded it, I made sure it was centered and on the bed. I went with the OEDK default of 0.2 mm layer height, 1 mm wall thickness, and 215 degrees Celsius printing temperature. I decided to change the default infill density from 15% to 10% because my slug didn’t need to be super strong. For my build plate adhesion type, I went with skirt, which ended up working perfectly.

 

I printed all of my FDM slugs on the Prusa i3 mk3. My first slug was way too big for the gum ball container, so I thought scaling my slug to be 45% of the original slice would work. It worked, but it was way too small and didn’t articulate how I wanted it to. So, I decided to scale my slug to be 75% of the original slice (83.90 mm long) so it could fit nicely in the gum ball container.

After printing four correctly sized slugs on the Prusa, I decided to tackle the SLA printer. Because I graciously gave myself a week until the assignment was due to use the SLA printer, I had room for error.  I decided to print the same size slug on the SLA printer as I did the FDM printers (the slug scaled 75%). I printed the slug in grey hard resin and upon taking it out and trying to move it, my slug unfortunately broke due to the force I was applying to its body. The resin supports bonded to the joints, which prevented the slug from being able to move, which led to me breaking it.

Because my first resin slug broke, I decided to scale the size down to 45% like I did the FDM slug that was too small for the gum ball container. I also printed this slug in grey hard resin; like the first one, the supports bonded to the joints and prevented the slug from moving. But, I didn’t break it this time because I learned from last time that if I tried too hard to move it, it would break. Luckily this one fit in the gum ball container, but it doesn’t bend, so its length is the exact length of the container.

In conclusion, I am happy to say that I ended up with five successful prints! Here’s a video of the articulation in action.

Cost Analysis: I asked for help from the lab assistants for about 30 minutes, so at $10 an hour, that totals to $5. On the FDM printer, I used 6.39g PLA for one print ($0.13), 0.59g for another print PLA ($0.01), and 3.11g PLA for 4 prints ($0.06), which totals to $0.20.  On the SLA printer, I used about 5g of material, which totals to about $1, give or take a few cents. The FDM machines spent about 2.8 hours printing, and at a machine cost of about $1.44/hr, that totals to $4.03. The SLA machine spent about 3.75 hours printing, and at a machine cost of about  $0.70/hr, that totals to $2.63. The gum ball machine containers cost about $0.20 each, and I used 5, so that totals to $1.00. This leaves me with a grand total of $13.86.