The task this week was to 3D print an impossible object which basically meant to find an object that could not be manufactured in any other way other than by using a 3D printing method. I started this project by searching for objects on Thingiverse that met this requirement. At first I found a knot that seemed really cool, but because the object was also size constrained to fit inside a gum-ball machine container, I was not able to print it correctly. Eventually, I stumbled upon this fish stl file. It is an impossible object due to its articulated body that allows it to move without the pieces coming apart. To ensure this object was printable, I first only printed one fish in the Prusa i3 MK3 printer. I also scaled it down to ensure that it would fit in the little ball. I used a raft and printed it flat on the bed. My layer height was 0.2mm and wall thickness was 0.1mm. Within 30 minutes I had my first fishy. The raft was a bit hard to remove so I had to be careful so as to not break the part. Additionally, I noticed that the size was actually smaller that I had visualized at first, but it fit inside the ball, so I decided to not change the scale for the other 3 FDM prints (I used the same settings for all of them and printed the 3 fish at once). Because the assignment required me to print 5 copies of the part using two different 3D printing methods, I also printed my fish in the resin printers available at the OEDK. I expected my part (due to its geometry and size) to be fused together during printing due to extra resin getting stuck between the correct parts and cured. So, I decided to print two fished one at the same scale as my FDM parts, and another one scaled about 10% greater that way I had a back up in case the smaller print fused together. When setting up the print, I printed the fish at an angle as I’ve been taught that is best for larger flatter prints. The overall print took only 1.5hrs. After the washing step (15mins) I removed the supports and realized that I had been correct. The smaller fish had fully fused together and was no longer articulated (it even broke) while the larger fish worked perfectly. I cured the two of them to fully cure the resin and my pieces were ready to go. This assignment was fairly simple as I had previous experience using 3D printers. However, the hardest part was finding (and choosing!) the impossible object to print.

Cost Analysis:

• Labor cost: 0.5hrs @ $20/hr → $10
• Filament cost: $0.30 (estimated from 3DprinterOS)
• Resin cost: $1.50 (estimated from PreFrom)
• Machine cost → negligible since we are using the machines available to us from the OEDK

Total cost → $11.80