My next assignment was to create an “impossible object” using 3D printing. This two requirements for this object were that it be something that can only be produced through 3D printing and that it fit inside a gumball machine capsule.

 

First, I browsed Thingiverse to find a good object to print. After a bit of searching, I found the Infinity Cube by mjdargen (https://www.thingiverse.com/thing:4997903). This cube has 8 hinged joints, allowing it to be inverted and folded infinitely. It is printed using a single STL and no assembly is necessary.

 

I then measured one of the gumball machine capsules with calipers to get an idea of the dimensions this cube would need to adhere to. I downloaded the STL file and scaled it down an appropriate amount. The size change wasn’t too drastic, so I was not worried about my tolerances being too small for the joints. I performed slicing with 0.15mm layer height, 1mm wall thickness, and a raft. I then generated a .gcode file to print the object.

 

I put this .gcode file on an SD card and put that SD card into the printer. My object began printing with no difficulty. I watched the print at first to ensure that the first layer was adhering to the bed well, then left it to run.

 

After the print completed, I took it off the build plate. I was very happy with the print quality!

 

I then began removing the raft. This actually proved to be quite difficult since it did not come off cleanly. After a while, however, I did succeed at removing all of it. I decided to just print with a brim rather than a full raft going forward.

 

Once the raft was off, I folded the cube to test its movement. It was slightly stiff for the first few turns but eventually got very smooth. It was fun to play with and I was happy with how it turned out!

 

FDM had been successful, but I had to choose a second printing method as well. I decided to use SLA. I used Preform to convert my STL and send my model to the printer. The print took about 45 minutes, at which point I returned and set it to wash. After the washing, I set it to cure. This whole process went smoothly, but unfortunately, my object was a little more “impossible” than intended.

 

Every cube and joint had been fused together. I was aware that resin printing was notoriously difficult for objects with small tolerances and moving joints, but I still decided to give it a shot. Now, I have certainly confirmed that to be true! I thought there may have been a chance that the cubes were just lightly fused together, so I applied some extra force to see if I got any movement. Sadly, all this did was snap my part into two pieces. On the bright side, I learned a valuable lesson and was now able to fit it inside the gumball machine capsule.

 

At this point, I considered switching to a different object that could be more effectively printed using both methods. However, the queue for each resin printer was ~10 parts long and I didn’t want to take machine time from someone who may have been patiently waiting to get their first print done. So, I decided to walk away with 4 functional FDM parts and 1 SLA lesson.

 

My final cost for the 5 parts comes out to be $36.12. I used 3DprinterOS for slicing, and it gave me an estimate of $0.24 for each FDM part. I then found that SLA printing is roughly double the cost for materials. The majority of this cost came from my time spent creating and finishing the part; 3D printing is generally a very affordable production method!