Recently, I have been working on 3D printing an “impossible” object for the 3D printing project. Since I had already 3D printed many things before, I knew how to utilize the Prusa 3D printers and the slicer software. I still appreciated the fact that we got to utilize the FormLabs SLA 3D printer and I got to learn something new. However, despite my prior experience with 3D printing, I found this project very frustrating for several reasons.
My Process
Initially, I had many ideas for the impossible object that I wanted to print. I found several files on Thingiverse that I thought were interesting including some moveable animals and interlocking chains. However, after considering the amount of iterations these likely would have taken to get right, the limited time I had due to other work, and 3D printer availability, I decided to change course to a simpler object. I settled on a “impossible box” which is a box inside a sphere that is too big to be removed from the box.
Figure 1. Impossible Box 3D Rendering
For my first prints, I decided to use the Prusa FDM printers since I had prior experience with those. I measured our capsules to be roughly 37 mm so I very foolishly decided to make my box 35 mm on 3Dprinteros. After setting up 3 boxes in a row, I printed the boxes without supports (another stupid mistake) and only a skirt . My print failed very quickly and I realized I needed to add supports so I tried again with auto-generated supports and a skirt this time. The print turned out well and I was pretty happy with my boxes. However, once I tried putting the box inside the capsule, I realized that it wouldn’t close.
Figure 2. Original FDM 3D Print Not Fitting
After my original 3D print did not fit inside the capsules, I scaled my object down to 3o mm and decided to reprint on the Ultimaker FDM printer. After the Ultimaker failed as well, I decided to print on the Prusa FDM printer again. This time, I utilized both the auto-generated supports and a raft on the print and was successfully able to print my impossible boxes. However, when I started trying to get the supports off, I realized that the auto-generated supports were extremely hard to remove since they completely surrounded all but one face of the box.
Figure 3. Auto-Generated Supports for FDM 3D Print
After struggling with pliers for a while and some super gluing, I was able to produce two impossible boxes that were FDM 3D printed.
Figure 4. 3D Printed FDM “Impossible” Boxes
For the SLA 3D print, I utilized the help of a lab assistant for most of it since I had never done an SLA 3D print before. After sending my file to the SLA slicer software, I used the one-click print feature to auto-generate supports and set it at the optimal orientation. Once everything was ready, I sent the file to the 3D printer and was ready to print. After the print was finished, I had to wash and cure the object as per the directions for the SLA printer. Unfortunately, since I printed the object on Friday and picked it up on Sunday, a lab tech had already washed and cured it so I was not able to go through that process. After my part was ready, it was time to break off the extremely annoying auto-generated supports.
Figure 5. Auto-Generated Supports for SLA Print
Since the supports for the SLA print were less all-encompassing and had areas where I could go in with pliers to break them off, I had an easier time removing the supports for the SLA print. Once the supports were removed, I had three SLA 3D printed “impossible” boxes.
Figure 6. 3D Printed SLA “Impossible” Boxes
Areas of Improvement
Overall, I definitely think that there are areas I could have improved on this project. Although I did not have too many issues with the SLA print, I do think that I could have removed the supports better so that my boxes were not as bumpy. Due to the shape of my object, I struggled to reach every little support and was not able to remove all the tiny bumps on my boxes. Other than that, however, I was pretty happy with how my SLA print came out as I had never done one before. I noticed how you can’t really see any of the individual layers on the 3D print and how the object itself felt much smoother than the FDM 3D printed objects.
Surprisingly, the part that caused me the most trouble was the FDM 3D printed boxes. Initially, I made the boxes too big which was just a stupid measuring mistake on my part. However, my prints did fail twice and I really struggled to find an open 3D printer several times. My biggest issue was the auto-generated supports and trying to get those out of boxes. Although I was trying to be gentle with my pieces, I ended up breaking both of my boxes on my final 3D print and, since it was late Sunday night and no printers were available, I was unable to reprint more. Although I did spend a good amount of time trying to super-glue some of the pieces, it is very obvious that my FDM 3D printed parts are glued together after the print.
Figure 7. Broken FDM 3D Print Reassembled
Additionally, I had one print where one piece was just too broken to be reattached. I tried super-gluing the pieces back together but they were too small and would not stay connected. However, the ball inside the box still was not able to leave the box so it is still an “impossible” box.
Figure 8. Broken Side of FDM 3D Print Box
Additionally, if I were to go back, I think I would have decreased the layer height and maybe increased the infill density. Although these are just stylistic choices, I would have wanted my FDM print to look more smooth.
Cost Analysis
For this cost analysis, I will be looking at the cost of: PLA 3D printer filament, SLA 3D printer resin, pliers, Prusa 3D printer, Ultimaker 3D printer, Formlabs Resin 3D printer, and the cost of my personal time.
For my original FDM 3D print of three boxes, 3Dprinteros says it costs about $1.01 of filament. Since I tried printing around three times (although some failed and some were bigger), I will say my failed attempts cost $3 of filament. For my final FDM 3d print, I only printed two boxes and it cost $0.57. For the SLA printer, the slicer software gave no estimate for how much resin I used but a bottle costs around $150 so I will approximate I used around $5 of resin. For pliers, I found some on the Home Depot website for around $20. The Prusa i3 costs $999, the Ultimaker 3 costs around $4,500 and the FormLabs SLA printer costs around $10,000. Finally, I spent around 6 hours on this project which, with my pay of $10/hr, costs $60. However, this does not include the amount of time that it took for the 3D prints to complete but, since I did not have to be present during that time, I did not factor it in.
Overall, this project costs $15,587.57 with machine costs however, considering the OEDK has the 3D printers and pliers available, it costs $68.57.
