Hello! Welcome to the third lesson in our "From Model to Object" module.
In our last session, we traveled back in time to understand the traditional, industrial workflow for creating struck medals. We saw how an artist's large plaster model was mechanically reduced using a Janvier lathe to create a hardened steel die. This process, a brilliant fusion of art and 19th-century engineering, was the standard for over a century.
Today, we leap into the 21st century. We will replace the reducing machine with your computer and Blender. Our goal is to prepare a 3D model in Blender for digital fabrication, considering specifications for 3D printing or CNC milling. Since you are already proficient in Blender, we'll skip the basics and focus on the specific workflows and technical requirements needed to turn a digital file into a physical object ready for molding or machining.
1. From 2D Image to 3D Relief: The Displacement Workflow
While you can certainly sculpt a relief from scratch in Blender—a process very similar to your physical sculpting work—one of the most powerful digital techniques is to generate a 3D relief from a 2D image. This is done using a depth map (or height map), which is a grayscale image where white represents the highest points (closest to the viewer) and black represents the lowest points.
There are now highly effective AI-driven tools that can analyze a photograph and generate a surprisingly accurate depth map. This map can then be used in Blender to "displace" the geometry of a flat plane, creating a detailed bas-relief.
Let's watch a tutorial that demonstrates two powerful methods for creating a relief in Blender.
Generate Depth Maps and Displace Super-detailed Bas-reliefs - Blender Tutorial
This video from Gleb Alexandrov, a well-known Blender artist, demonstrates two excellent digital relief creation techniques. The first is the displacement method using a depth map, and the second involves combining existing 3D models.
Please watch the following sections: (00:00 - 04:15) Focus on the methods for generating a depth map from a 2D image. Notice the significant quality difference between older methods and modern AI-based tools. (04:15 - 10:18) Observe how the depth map is applied to a subdivided plane using the 'Displace' modifier. Pay attention to how he corrects the UV coordinates to prevent stretching. (10:18 - 15:35) Watch this alternative workflow, where existing 3D models are arranged and then projected onto a plane using the 'Shrinkwrap' modifier. This is a form of digital kitbashing that can produce complex results quickly.
These techniques provide a robust starting point for your digital model. Whether you generate a relief from an image or compose one from various 3D elements, the next step is to prepare that model for manufacturing.
2. The Digital Pre-Flight Checklist
Before a 3D model can be sent to a 3D printer or a CNC mill, it must meet several technical requirements. Think of this as a pre-flight check to ensure a successful fabrication process.
A. Make it Solid and "Watertight"
A 3D model for fabrication cannot be an infinitely thin surface. It must be a manifold (or "watertight") object with defined volume. This means it must have no holes, and every edge must connect to exactly two faces.
In the video you just watched (at 15:35), you saw one way to achieve this: selecting the boundary loop of the relief, extruding it downwards, and filling the bottom to create a solid base. The Remesh modifier was then used to create a clean, uniform topology.
Another common tool for this is the Solidify modifier, which adds thickness to a mesh.
B. Know Your Machine: CNC vs. 3D Printing
The method of fabrication dramatically influences your design choices. For medals, the two primary digital routes are:
- 3D Printing: Used to create a high-resolution master model (typically in resin), which you can then use to create a silicone mold for casting metal—a process you're already very familiar with.
- CNC Milling/Laser Engraving: Used to machine a die directly into metal (like steel or brass). This die is then used for striking medals.
These processes have different capabilities, especially regarding fine detail.
CNC vs 3D Laser: Best for Coin Dies & Precision Molds?
This article from HeatSign provides an excellent comparison between traditional CNC milling and modern 3D laser engraving for making dies.
Please read sections 1, 2, and the comparison table in section 3. Focus on understanding the 'Radius Problem' of CNC milling and the 'Zero Radius' capability of laser engraving. This directly impacts how you should approach sharp corners and fine details in your Blender model.
As you read, for CNC milling, you cannot create an interior corner that is sharper than the radius of the cutting tool. This means tiny, sharp details and incised lettering can be problematic. Lasers and 3D printers, however, excel at this. This knowledge should guide your design decisions from the start.
C. Remember Draft Angles
Just as with struck medals, if you are designing a part to be removed from a mold or a die, draft angles are critical. For a CNC-milled die, vertical walls are impossible. You must incorporate a slight taper to allow the tool to move and the final struck medal to be released.
While not strictly necessary for a one-off 3D print, it's a crucial habit for any design intended for replication.
D. Exporting the File
Once your model is solid, scaled correctly, and has all design considerations accounted for, the final step is to export it. The most common formats for digital fabrication are STL (Stereolithography) and OBJ. In Blender, you can do this via File > Export > Stl (.stl).
3. A Case Study: Trial and Error in Coin Making
Theoretical knowledge is useful, but seeing it applied in a real project is invaluable. The following forum thread is a fantastic step-by-step account of a user learning Blender specifically to create a 3D-printed challenge coin. It perfectly illustrates the iterative process of designing, testing, and refining a model for fabrication.
Creating Challenge Coins with 3-D Modeling Software
This forum post provides a candid, real-world look at the process of creating a challenge coin in Blender and the realities of 3D printing it.
Please read through this forum post. You can skim the text, but pay close attention to the images and the author's descriptions of the problems encountered. Specifically, note: Sections 1 & 2: How they combine existing 3D models and add text. Section 4: The results of the first test print. Notice the discussion of flaws like layer lines, loss of detail at a small scale, and how the incised letters have 'fused' together. Section 5 & 6: The decision to abandon incised lettering and switch to raised letters, leading to a much cleaner final print. This is a classic example of adapting a design to the limitations of the fabrication process.
This case study is a perfect lesson in design for manufacturing. The initial design with incised letters was aesthetically fine on the computer screen, but it failed in the physical world due to the nature of resin 3D printing at a small scale. The successful design was one that respected the physical limitations of the process.
Conclusion
You now have a framework for taking a design from a concept to a fabrication-ready file in Blender. This digital workflow offers incredible flexibility, allowing for rapid iteration and complexity that would be difficult or impossible with traditional methods.
Key Takeaways:
- You can create a 3D relief in Blender by sculpting, using depth-map displacement, or by combining existing 3D models.
- Before fabrication, a model must be made solid and watertight, often using the Solidify modifier or by manually extruding and closing the mesh.
- Your design choices must be informed by the fabrication method: CNC milling has limitations with sharp internal corners (the "Radius Problem"), while 3D printing and laser engraving can achieve finer detail.
- Practical testing is essential. As the case study showed, a design may need to be modified after a test print reveals unforeseen issues like detail loss or feature fusing.
In our next and final lesson, we will address the last step in bringing your medal to life: selecting appropriate patination and surface finishing techniques to enhance the beauty and narrative of the final metal object.