Piranhas have invaded the OEDK! There everywhere – on the tables, in the Maker Bar, and even on the 3D printers! How did they get there in the first place?
The piranhas were first conceived from the birthplace of all CAD files: Thingiverse. Given my inability to come up with my own CAD models, I was under the constraints of pre-existing files that I could “borrow” from the web. In thinking of “impossible objects”, or objects that can only be easily manufactured with a 3D printer, my mind wandered off to geometric shapes, and I landed on a Klein Bottle. However, that did not seem a fun enough item to get from a gumball machine. The last thing I wanted my 3D prints to be was disappointing, so I surfed Thingiverse some more until I stumbled upon PIRANHAZ by muzz64.
The reason this is an impossible object is that it has two “buttons” that go through holes in the body of the piranha, and these buttons can be pressed to make the jaws of the piranha open and close. I could not think of any traditional manufacturing method to produce such an item.
I thought I was one step closer to bringing these piranhas to life when I promptly downloaded the file. However, when I tried uploading it to 3DPrinterOS, no CAD model that could be sliced. I was alerted by someone else that I had to download a .stl file. I have no idea what I initially downloaded, but the .stl file worked!
I scaled the model to what I thought was an appropriate size, sliced it, chose the wall thickness/infill/layer height settings (applying what I learned from the 3D printing module on Canvas), and sent it to the printer. I felt so powerful! It was my first ever print. I realized one problem, though: I might have slightly overestimated the size of the print. It was absolutely tiny, but it looked so cute.
I rescaled the piranha such that its length would be slightly smaller than the diameter of the flat side of the capsule it would be put it for the gumball machine. I sliced it and opted to print it without a raft or supports to test the outcome. It overall turned out great, but there was a very slight imperfection in the overhang parts of the buttons. Striving for perfection, I decided to test out different variations to get the exemplary piranha.
I added a raft to enhance adhesion to the plate and supports for the overhang regions. I noticed two things: the bottom side of the piranha is slightly different from the top side from peeling away the raft, and internal supports were generated that increased friction and restricted the motion of the jaws. I was unfortunately unable to find a solution to the raft dilemma, but I got advice from a Lab Assistant about the internal supports: I should instead use PrusaSlicer to slice the CAD model, and use PrusaSlicer I did.
PrusaSlicer had a myriad of more advanced settings than 3DPrinterOS, and I spent a lot of time exploring the different features. I was able to disable internal supports with the click of a button, and I was able to reduce the number of layers in the raft to 2 (which I could not figure out how to do with 3DPrinterOS). I exported the G code to 3DPrinterOS and printed again. This time, the results were immaculate (minus the difference between the top and bottom layers).
I printed 4 piranhas with the FDM Prusa printers, but I had to print a 5th with another technique. This is where things got a bit messy. The obvious technique was SLA, but every time I went to the OEDK, it was in use. Prints simply took to long on the SLA printer, and living off campus was quite disadvantageous as I could not go late at night or early in the morning. Instead, I had to wait until the last day when it became too urgent to wait around. By then, only one of the SLA printers was supposedly functional, as all OEDK machines tend to a higher state of entropy with time.
Someone told me that we could print multiple items simultaneously, and the print time would only marginally increase. As such, I collaborated with other people with poor time management to get our prints done all at once. After 4 hours of printing at 1 AM, it was a slap to the face to see that only the supports of my item were printed. The piranha was drowning somewhere in the resin.
Take 2. I was printing another piranha with other people’s prints. I stayed the night at the OEDK, impatiently waiting for the print to finish. As a backup, I decided to use the FDM UltiMaker printer to print a piranha. Even though it uses the same technique as the Prusa printers (FDM), it was still another brand of printer that could serve as my last resort. However, I could not export G code to the UltiMaker, so I had to rely on 3DPrinterOS to slice the file and generate supports. As such, internal supports were also generated, and the resulting piranha had paralyzed jaws. The SLA print had to work.
Fast-forward to 8 PM, and after getting only 2 hours of sleep, I went to the OEDK to check on the print. To my horror, only the supports were printed again. I decided to print the piranha with the printer that was supposedly past its lifetime (after getting permission by Danny). It would be done in 2 hours, so I went to class and came back at 11. It was now or never, as I did not have enough time for another round.
IT WORKED! I was absolutely ecstatic. It was gorgeous. I washed it and cut off all the supports. Before curing it, I pressed on the buttons multiple times to loosen the resin up so that the jaws could still move. I then cured it for 15 minutes, and a resin piranha was born. The jaws are not as smooth as the FDM prints, but they still moved, which I believe is quite the accomplishment to achieve with SLA. I lightly sanded all sides with 400-grit sandpaper to establish a smooth surface, and I washed it to remove the resin particles.
In the nick of time, I was able to put my 5 piranhas in their capsules and write the link to the CAD file on Thingiverse on pieces of paper to be put in the capsules as well. I was exhausted, I was sleep deprived, yet I was triumphant.
Disregarding the SLA printer, I had a lot of fun with this assignment. I was carrying piranhas on me all the time, and I would showcase them to all my friends. I even showed them to the Lovett Magister, Dr. Mike Gustin, and he requested that I make him a piranha. I also learned how to correctly spell piranha. The possibilities are vast now that I know how to use the 3D printers; I only need to learn how to create CAD models for the possibilities to be limitless.
MONEY TIMEEEEE 🤑
- $0.14 for each FDM piranha, as shown in 3DPrinterOS –> $0.56 for four FDM piranhas
- $0.14 for a single SLA piranha (cost is assumed to be equal to that of FDM piranha because I have no idea how to calculate the cost of the resin used)
- $10/hour of labor –> $40 for four hours (even though 3D printing is mostly passive waiting, I am including the transportation time to and from the OEDK, as that was a huge time sink)
—–> $40.70 per 5 piranhas, or $8.14 per piranha. Selling it for a quarter in the gumball machine is quite the steal.
brianbishara
