It’s 3D printing week, and there’s a chill in the air. I, for one, have been fully embracing the autumnal mood, particularly via making myself countless cups of instant apple cider. As such, when prompted with 3D printing an object that is engaging, impossible to create through traditional processes, and capable of fitting inside a gumball machine capsule, I searched Thingiverse for a design that would help celebrate the season. Fairly quickly, I found a design for a pumpkin made of eight 3D gears, and it was love at first sight. The different pieces came together to form such a cohesive image, yet they were also capable of mechanically interacting in a very sophisticated manner. Below is a photograph of the object from the website, and other photographs/info about the design (including a cool video of it being used) can be found here.

I wanted to use this project as an opportunity to try out the wet lab printers, but before doing so, I needed to make sure that the design could be sized down to fit in a gumball machine capsule while still being functional. Thus, I decided to make an initial print on one of the cheaper FDM machines in the OEDK proper. To determine which scale to use, I found that the smaller dimension of the capsule was its diameter, measuring at about 47.5 mm. Additionally, the Geared Pumpkin design is roughly spherical much like the gumball machine capsules, so there was no concern of the object having corners that couldn’t fit in the round container. Therefore, if I sized the design down such that each of its overall dimensions was safely under 47.5 mm, I should have no problem fitting the object into the capsule.

Luckily, the creator of the design had prepared a file of the full assembly, which, while unprintable, would allow me to gauge how large my print would be when all its pieces were put together. I opened this file in Simplify3D and sized it down until all three dimensions were at least 4 mm less than 47.5 mm, as I am not one to tempt fate. At this point, the scale of the object was 49.78%. Could I have rounded it up to 50%? Probably. Was I going to risk it? Not a chance.

Looking further into the 3D files for the Geared Pumpkin design, I found that the creator had also prepared a print file of all of the object’s pieces: eight gears, a central core structure, and eight connector pieces. Scaling this file to 49.78%, I proceeded to print it on one of the free FDM printers.

My first print was not perfectly successful, however, because of the support material generated within the central core. I had used Simplify3D’s default settings, which generate support material in any regions that could conceivably collapse, such as the holes of the Geared Pumpkin’s central core. However, these holes are very small, so it is practically impossible to remove this support material, as shown on the right. After trying to jam connectors into the central core anyway and breaking several in the process, I started a new print of just the core and the eight connector pieces, this time without support material. On the other hand, all eight gears had come out very nicely, as shown below.

Despite the danger of printing without supports, my second central core was essentially flawless, and the connector pieces fit into it perfectly. Thus, I was able to assemble the entire object with little difficulty. I first tried fitting the pumpkin inside a gumball machine capsule, and as seen on the left, it fit just fine. I then tried to spin the system’s gears and found that they worked as intended. As I tested the gears, I noticed that if they are initially positioned so that they form a perfect pumpkin, it takes several rotations for the gears to sync back up into that perfect pumpkin shape as a result of their different sizes. I was also worried that the pumpkin was asymmetric and its stem a little deformed, but when I looked back at the creator’s assembly file (shown below), I realized that these were intentional design choices so as to make the pumpkin look more realistic. Thus, I was very happy with this iteration of the Geared Pumpkin and recorded a brief video of me using it, which can be seen further down.

 

I then sought to create a higher-quality model with the wet lab printers, but that’s where the classic plot twist comes in. At lab assistant recommendation, I used the Dimension printer, which generates support material that can be dissolved away in the lye bath. However, the pieces resulting from this print were of a significantly lower quality than those in my initial print, with globby layers that didn’t always line up with each other, as well as one gear tooth that inexplicably curled upward (i.e., away from the base of the print). Nevertheless, I decided to place the pieces in the lye bath so that I’d know how to use it, as well as hoping that the lye would miraculously smooth the globby edges of the pieces. However, the lab assistant recommended that I simply drop my pieces onto the surface of the lye rather than submerge them in the cage because “they look very fragile, and you don’t want the lye to eat away at them too harshly.” I wasn’t sure of the chemistry logic of this statement, but I trusted the experience of this veteran lab assistant, so I dropped my pieces into the lye and decided to retrieve them early the next morning, lest my oddly placed pieces become an inconvenience to anyone else.

When I removed the pieces, though, the situation was as one might expect. Only some of the half-submerged pieces’ supports had dissolved, while some holes were still clogged as ever. Furthermore, the quality of the gears was no better than it had been the night before, so I decided to abandon the newest set of pieces entirely. While I would’ve liked to experiment with the remaining wet lab printers, I didn’t have time this week for iterations upon iterations, so I decided to backtrack to a method that I knew could produce objects of a much higher quality than that which I had just created: the FDM printers in the main part of the OEDK.

One question still remained: should I sand the pieces of my pumpkins, or should I leave them as is? I decided to sand down a gear from my original print to see if I preferred the resulting texture over the default one. After sanding this gear down with sandpapers of decreasing grit sizes, I found that the surface was significantly smoother, but it was also slightly discolored and had a much more raggedy appearance. I decided that I liked the default texture better, particularly because the way in which each gear is printed with its outer face pointed upwards such that its surface has a cool topographical effect. With my aesthetic decisions solidified, I set out to make my final prints.

I printed my first new copy on a different FDM printer than before, with very different results. It appeared as if this printer had a larger extrusion nozzle diameter, as the gear teeth were in no way pointy, and the connector pieces didn’t fit into the holes. With an unusable batch, I began a new print on a third machine, but this time, some of the half-printed pieces were somehow knocked out of position while I was away, resulting in the formation of “tumbleweeds” as the machine tried to print new layers atop absent objects. I stopped this print, added rafts to the print settings to help hold the pieces in place, and began the print again. At this point, the FDM printer that I originally used had become available, so I started another print on that printer, this time adding rafts.

Both of these rafted prints were successful, although one print’s rafts were denser and were easier to peel off, while the other print’s rafts were less dense and broke upon peeling, requiring sanding to remove stubborn strands of raft. I assembled both sets of pieces and found that, confusingly enough, both prints’ gears slipped off of the connector pieces more easily than those of my original print. It was as if the connectors were somehow looser than before. To resolve the situation, I picked the less loose of the two new prints and swapped out the more troublesome connectors for connectors from previous failed prints. This resulted in an assembly with sturdiness comparable to my original print. Then, rather than printing a second new object, I simply printed a new gear to replace the sanded one on my original print, thus making it good as new. At last, I had two complete assemblies of the Geared Pumpkin, which can be seen below.