To become familiar with using 3D printers at the OEDK, we were tasked with printing an impossible object from Thingiverse that would fit inside a gumball machine capsule. I chose the object “Impossible Box” by bkidmose.
“Impossible Box” by bkidmose.
I chose this object because I believe the fact that it has a moving ball in the center will make it fun to play with. Since we had to use at least two different printing techniques, I chose to do FDM printing using the Prusa printer and SLA printing using the Formlabs Form 2 printer.
I started off by printing with the Prusa because I knew it would be the faster of the two processes and figured it would be easier to correct any mistakes. To do so, I first downloaded the stl. file for the object and uploaded to 3D Printer OS. The object was too big (55mm per side), so I scaled it down to 25 mm per side.
Scaling the object on 3D Printer OS.
After scaling the object, I lowered the infill of the print to 15% rather than 20% so that it would print faster. Then, I sliced it and sent it to the printer. It took approximately 30 minutes to print each box, so the total print time for four boxes was two hours and seven minutes.
One finished box on the Prusa printer.
To post process the box, I removed its support material with pliers. I didn’t face any challenges in the actual printing process, but I did struggle to remove some of the support material. Particularly, the support material at the base of the sphere was difficult to take off and I had to remove part of the actual material in the process.
The flawed bottom of the sphere.
After printing with the Prusa, I went on to use the Form 2 printer. I kept the same scale for the box, since I knew it had worked previously. I used the Preform software to upload the file and prepare the print (I rotated the piece on the bed to minimize contact and selected to auto generate support material). I ended up doing my print with Kaede, who was also working on her homework at the same time. Since we printed both of our objects together, the print time was three hours.
After the print, the parts were washed in alcohol for 10 minutes to remove excess resin and were then cured with UV light for 20 minutes. The parts were sticky after the initial curing, so the two steps were repeated.
The parts before being washed.
The parts after being washed.
Once my parts were washed and cured, I completed my final post-processing step, removing the support material. I used a shear cutter to cut off the supports and then sanded the points of contact between the supports and the part, since small artefacts had been left. In the process of removing the support from one of the boxes, I accidentally snapped the edge of one of the boxes. I had made an extra box with the Prusa, so I chose to use that one instead of the cracked box.
The cracked edge of the box.
After post processing, I printed out a slip of paper with the part’s information (designer and link) and stored each paper along with the part inside a gumball capsule.
The final boxes.
Cost estimate
Labor
- Approximately 2 hours of labor (finding the part and post-processing)$15/hour = $30
Material
- $0.07 for each box printed on the Prusa (0.07 x 4)= $0.28
- Cost of printing on Form 2= $2.3-$3.12 per cubic in, average of $2.71 per cubic in (($2.3+$3.12)/2)
- Volume of 1 box= 3.86 mL=0.2355517 cubic in
- 0.2355517 x $2.71 = $0.64 per box
- 5 gum ball capsules ($0.10 per unit from SmileMakers)= $0.50
Equipment
- Membership at a makerspace to use the same equipment (TXRX Labs)= $50
Total cost: $30 + $0.28 +$0.64 + $0.50 + $50 = $81.42
