For my 3D Printing assignment, I was tasked with designing and producing an “Impossible Object”—something that could only be manufactured using 3D printing techniques. Given that this would be my first time 3D printing, I wanted to tackle something visually compelling, technically challenging, and practical enough to serve as a desk accessory or organizational piece. I landed on a DNA-inspired double helix design with interlocking features that created internal spaces. Here’s how I tackled the process and what I learned along the way.

Initial Design Thoughts and Challenges

When brainstorming my impossible object, I initially considered creating a representation of the Runge-Kutta 4 (RK4) algorithm—an ode to my background in mathematical modeling. RK4’s structure was visually appealing but would demand intricate, interconnected structures. That is why, after considering the constraints of FDM and SLA printing, I realized that such a design would require extensive support structures, leading to tedious post-processing. This ruled out my original design as an ideal fit for FDM and SLA.

Switching gears, I looked at other options that could still capture complexity and elegance. I found inspiration in DNA’s double helix structure, which perfectly balances aesthetics and functionality. The double helix is deceptively complex but has a beautifully symmetrical structure, making it both a captivating visual and structurally robust. With this in mind, I chose from Thingiverse a model that starred an open structure that could hold small objects, like pens, tickets, or napkins—making it useful while still fulfilling the “impossible” criteria.

Defining Impossible: DNA Helix Meets 3D Printing

The double helix model satisfied several key “impossible object” requirements:

• Internal Geometry: The DNA-inspired shape has intertwining, enclosed sections that would be impossible to carve out using traditional manufacturing.
• Interlocking Features: The helix’s twists naturally form complex internal spaces, which would require considerable engineering effort to replicate by other means.
• Practical Size and Purpose: I scaled the model to fit within a standard gumball capsule, transforming it into a compact, multifunctional piece. Its open structure allowed for practical use while still showcasing intricate detail.

The 3D Printing Process

After finalizing the design, I began the actual printing process. This required balancing the requirements of two different 3D printing techniques: FDM (Fused Deposition Modeling) and SLA (Stereolithography). Here’s how each of these processes played out.

First Attempts with FDM

I started with FDM printing, as it’s generally faster and uses a less expensive filament. FDM was also an approachable first step, given the DNA helix’s open design and relatively simple support needs.

1. Initial Setup and Scaling: I scaled the model down to fit within the gumball capsule’s dimensions using Bambu Studio Slicer. To achieve this, I measured the capsule’s dimensions with calipers, then applied a 40% uniform scale to the model. This ensured that the part fit precisely within the constraints of the assignment.
2. First Print Attempt: As a beginner, I relied on the recommended settings for small prints: a layer height of 0.15 mm, wall thickness of 1 mm, and infill density of 15%. I loaded white PLA filament and printed the piece on Bambu Printer #3. The initial print was completed without supports, but the final piece lacked the desired structural detail and quality. 

3. Refining the Settings: After consulting with a lab assistant, I modified the settings to achieve a higher quality print. I adjusted the layer height to 0.1 mm, reduced the wall thickness to 0.25 mm, and increased the infill density to 25%. Disabling supports proved beneficial for this design, as it prevented support material from obstructing the intricate internal structure.

4. Final FDM Prints: Using these refined settings, I printed three pieces: first, the trial piece, which took about an hour to complete, and then, once I knew the used settings had worked, two additional replicates, which took approximately two extra hours to complete. On these results a higher quality finish with smoother curves and clearer details in the helix structure can be seen. Below, the image shows the contrast between the first try (unsuccessful) and the second (and final) one.

Trying SLA for Higher Resolution

With the FDM prints successfully completed, I moved on to the SLA process. SLA printing offers finer detail and smoother surfaces, making it ideal for an intricate design like the double helix.

1. Preparing for SLA Printing: I set up the model in PreForm Slicer, ensuring it maintained the 40% scaling used in the FDM process. I followed the recommended settings in the course instructions, using Tough 1500 Resin V1, a durable material suited for small parts with detailed geometry. After generating the file, I used the software’s auto-support function, which strategically placed supports on the model’s more fragile sections.

2. Printing and Curing: I printed three SLA pieces simultaneously, all of which took around 5.5 hours. After printing, I rinsed the parts to remove excess resin and left them to dry for 20 minutes. The pieces were then cured under UV light for an additional hour to harden the resin, ensuring durability.

3. Removing Supports and Post-Processing: This step was delicate and time-consuming. Using a variety of pliers, I carefully removed the supports without damaging the helix’s delicate strands. I printed an additional SLA piece as a backup, which wasn’t necessary as (luckily) no print was broken during the removal of the supports. By the end, I had three two-quality SLA models, each with smooth surfaces and sharp details. 

This way, I had the 5 replicates of the printed object that the homework requested, as it can be seen below. In white, we see the FDM results while, in gray, the SLA.

Reflections and Lessons Learned

This project was a fantastic introduction to the world of 3D printing. I learned a lot about the intricacies of both FDM and SLA printing, each with its own strengths and limitations:

• FDM vs. SLA: FDM was quicker and allowed for easy iteration. Even though I know this technique tends to struggle with fine details, in this case it did just fine with the helix structure. SLA, while offering slightly superior detail, required extensive post-processing and was more time-intensive.
• Choosing Materials and Techniques: I initially underestimated the importance of selecting the right material and process for each part of a project. In future projects, I’ll spend more time assessing model features and understanding which printing method will best bring them to life. This was something that I realized I had never thought about, that is, until I was trying to choose between the RK4 model and the double helix.
• Patience and Precision: 3D printing takes time—not only in the actual printing but in setup, post-processing, and troubleshooting. I learned to be meticulous in each stage, and that careful planning pays off in the final product.

Completing this assignment gave me confidence and inspiration to push my boundaries in future designs. I’m excited to explore new projects, experiment with different 3D printing methods, and create more complex, functional pieces that combine beauty and utility.

Cost Breakdown

Cost Type	Cost per Unit	Quantity/Time	Total Cost
Materials
PLA Filament (FDM)	$0.05 per gram	~25.41 grams (Calculated based on 33.87 cm³ volume and 25% infill for three FDM prints.)	$1.27
Tough 1500 Resin V1 (SLA)	$0.12 per gram	~101.61 grams (Based on 33.87 cm³ volume per piece for three SLA prints.)	$12.19
Machine Time
FDM Printer	$2.00 per hour	3.67 hours	$7.34
SLA Printer	$3.00 per hour	6 hours	$18.00
Post-Processing
Curing and Drying (SLA)	$3.00 per hour	1.5 hours	$4.50
Support Removal & Finishing	$15.00 per hour	1 hour	$15.00
Grand Total			$58.30

Cost per Piece

For this project, I am particularly interested in the cost of the used techniques compared with each other:

• FDM Cost per Piece:
  • Materials: $1.27 / 3 pieces = $0.42
  • Machine Time: $7.34 / 3 pieces = $2.45
  • Total FDM Cost per Piece: $2.87
• SLA Cost per Piece:
  • Materials: $12.19 / 3 pieces = $4.06
  • Machine Time: $18.00 / 3 pieces = $6.00
  • Curing & Post-Processing: ($4.50 + $15.00) / 3 = $6.17
  • Total SLA Cost per Piece: $16.23

Conclusions

The whole experience highlights how FDM Printing is more affordable per piece, largely due to the lower cost of materials (PLA filament is much cheaper than SLA resin) and faster machine time. Because of this, we can take FDM to be an efficient technique to use for functional prototypes or simpler designs where extreme precision isn’t as critical. Instead, SLA Printing in general yields higher resolution, smoother surfaces, and greater precision, which is valuable for very complex designs that demand fine detail. However, the overall cost per piece is a lot higher due to the cost of resin, longer machine times, and the need for more post-processing steps like curing and support removal. 

In this case, the use of SLA is not justified. As it can be appreciated in the photo below, the quality does not vary that much while the time it requires is a lot more.

Finally, in terms of the overall cost of the experience, as 3D printing continues to grow across industries, gaining hands-on experience with different methods like FDM and SLA is invaluable. The ability to create customized, complex, and impossible-to-manufacture objects opens up innovative possibilities, especially in biomedical engineering, where rapid prototyping of medical devices and models can accelerate development and tailor solutions to specific needs. Because of this, despite the initial investment in materials, machine time, and post-processing, learning 3D printing is increasingly valuable and totally worth it.