The first assignment of the semester was to create an “impossible object,” an object that could only be created practically using a 3d printing method, that could fit inside of a gumball capsule.

To begin my project, I went onto Thingiverse and browsed the potential prints I could make. I settled on a hollow truncated cube that housed a sphere inside of it.

I decided to first try FDM printing my objects on the Prusa i3 mk3s and used the OEDK’s default slicer settings with supports and a skirt. I ended up scaling down the object to 75% of its original size (40x40x40 mm to 30x30x30 mm).

The print came out fairly nice and I had no trouble taking off the supports. However, one part of the sphere came out rougher than the rest so I wondered if a different orientation would reduce the rough area of the sphere. I also noticed that there was slight warping on the side that was attached to the bed and wondered if a raft would help.

So then, I tried printing three of my objects at once, but flipped 180 degrees in the y axis so that the tiny cylindrical protrusion out of the sphere was pointed upwards instead of down towards the bed. I also used a raft instead of a skirt, but kept the same default slicer settings.

Unfortunately, the Prusa glitched and about 75% of the way through, all of the layer shifted slightly and resulted in the rest of the layers being off set. I was not sure what happened, but I assumed that the printer had lagged or paused and resulted in a shift.

Thankfully, with another run, my prints were successful. I had used the same settings as before and they

From here, I decided to try out the SLA printing method. I used the preform machines in the wet lab to try printing my truncated cube. I decided to take out the internal supports in hopes that it would be easier during post processing to pry off the supports from the internal sphere. Otherwise, I kept the default settings. After my object printed, I had to let it sit in a wash for 15m, and then cure it for another 15 minutes at 60 C. Between the wash and the cure, I tried my best to take off, or at least detach, some of the supports. After curing, I took off the rest of the supports, and noticed that the surface was rough where the supports had been and had to try and sand them down. Overall, the quality of the part was far superior to the FDM printed pieces. The only downside was that the sphere would not spin.

 

Cost Analysis: FDM

32.09 g x2 = 64.18 g of PLA

Print time total: 4h44m x2 = 9h 28m

Cost of materials: $0.64 x 2 = $1.28

Labor: Proficient in FDM printing/using Prusas, so no assistance needed from lab techs.

Cost analysis: SLA

20.32 mL of resin

Print time: 2h 27m

Wash and Cure time: 30m

Total time : 2h 57m

Cost of materials: $175/1000mL –> $3.56

Labor Cost: 30m from lab assistants@ $10/hr –> $5

Total Cost: $8.56