Custom CNC Bases for a Mineral Collection Using Close-range Photogrammetry

This project documents a complete workflow for creating a 3D model impression of a mineral in sand, and producing a custom milled acrylic base using photogrammetry, 3D modeling, and CNC machining.

The process consists of the following steps:

1. Photographing the Sand Imprint. Capture high-quality photos of a mineral pressed into sand, ensuring good lighting, sharpness, and coverage from multiple angles. Printed calibration markers (12-bit single ring) are placed around the imprint for scaling and alignment.
2. Generating the 3D Model with RealityCapture. Import the photos into RealityCapture, detect markers, define scale using the marker distances, align the images, and generate a mesh. The 3D model is exported in .stl format.
3. Model Cleaning in Fusion 360. Import the STL into Fusion 360, set the workspace to meters, and reposition the model. Trim excess geometry using the mesh cutting tool to isolate only the sand imprint. Reposition the model to align it properly with the build surface and export the cleaned STL.
4. Preparing for CNC Milling with Easel Pro. Set up the project in Easel Pro: define material (cast acrylic), import the STL model, adjust cut settings and origin (Z-height from the top surface), and configure the roughing and finishing toolpaths.
5. Milling the Acrylic Base with a CNC. Mount the acrylic piece, define work zero using a Z-probe or manual method, and run the milling job in two phases: roughing and finishing. After milling, clean the piece and test the fit of the mineral in the recessed shape.

🔗 The original documentation is available in Spanish at our personal web buenabase.eu.

All brands shown are for informational use only — no commercial affiliation.

*This translation was done with the assistance of ChatGPT.

Each step includes a detailed list of required tools and materials.

To create a precise negative mold of your mineral specimen, we use kinetic sand (also called "magic sand") as a molding medium. It's reusable, easy to shape, and captures detail surprisingly well.

🛠 What you'll need:

1. A plating mold (any circular or square frame) painted to avoid reflections
2. Kinetic sand
3. Your mineral specimen
4. A flat workspace
5. Modeling tools

🧭 Instructions:

1. Fill the mold ring with kinetic sand to the top. Lightly compress it — firm, but not rock-hard.
2. Flip the mold upside down so the flattest surface is now on top. This ensures a smooth contact surface for the scan later on.
3. Choose the best pose for the specimen, paying attention to its natural balance and stability. The chosen orientation should match the piece’s center of gravity to avoid future wobbling when mounted.
4. Lower the mineral into the sand slowly, aiming for a depth of about 15 mm (maximum cutting depth of a ⅛" end mill).
5. Do not press too hard. Gently press the piece while observing if it stays level. Lift and adjust as many times as needed until it's balanced and visually pleasing.
6. Once the mineral is in place, press slightly deeper — this extra depth acts as a trimming margin for the 3D model. The top surface may deform slightly and will later be cleaned up digitally.
7. Before removing the piece, gently shift it side to side and up-down to compact the surrounding sand and strengthen the imprint.
8. Lift the specimen vertically with care, watching for any loose sand displacement.

🧼 Refining the Mold:

1. After removal, inspect the mold from above. If there are loose areas or overhangs, smooth or compact them. CNC machines cut perpendicularly — so any overhang could obstruct the tool path.
2. Use a modeling tool to unify concave or rough areas, without altering the shape.
3. You can now reinsert the mineral to verify the fit. If it's unbalanced or misaligned, adjust and repeat until you're satisfied.

💡 Tip: You could also refine the 3D scan later in Meshmixer, but we find that physical editing of the mold yields better fidelity and less digital cleanup.

Now that we’ve made the mold, it's time to digitize it using close-range photogrammetry. This allows us to generate a 3D model suitable for CNC machining.

🛠 What You’ll Need:

1. A manual turntable. We used the SNUDDA from IKEA.
2. A3 white cardstock or white paint
3. Black background (cloth, paper, foam board, etc.)
4. Printed control point markers (📌 You can generate the photogrammetry marker template using Reality Capture or download it directly from this link: https://www.buenabase.eu/sdc_download/3444/?key=4v9j1nx3irapg52uk0fpss8a6c1bjh)
5. Tripod and DSLR or mirrorless camera
6. Two diffuse lights (softboxes or lamps with diffuser paper)
7. Photo editing or photogrammetry software (e.g., RealityCapture)

⚙️ Setup:

1. Prepare the turntable: Cut white A3 cardstock to fit your turntable surface or paint it white. A uniform, matte surface helps eliminate shadows and glare.
2. Set up your backdrop: Place a black background behind the turntable. The strong contrast between the white base and the black background helps the software clearly identify the "floor."
3. Place the marker sheet: Center the printed marker pattern on the turntable, then place your sand mold inside the marked area.
4. Lighting the scene: Use two diffuse light sources (e.g., softboxes or lamps with tracing paper) at roughly 80° angles — like the hands on a clock at 11 and 1 o’clock. The goal is to avoid harsh shadows, especially inside the mold.

Example setup:

1. Two DIY softboxes
2. LED bulbs (35W, equivalent to 350W), 5700K, CRI 93+

📷 Camera Settings and Shooting:

1. Camera configuration
2. ISO: 100–200
3. Aperture: f/16 to f/22
4. Mode: Aperture priority (camera auto-selects shutter speed)
5. Lens: 50mm fixed (to avoid zoom distortion)
6. File type: JPG (Large or Maximum Quality)
7. Overhead (zenithal) photos: Mount the camera directly above the setup. Make sure all four markers are visible.Take at least 4 overhead shots, rotating the turntable slightly each time. This ensures backup images in case marker recognition fails in one of them.

💡 Tip: One well-lit zenithal shot is technically enough — but more is safer.

1. Oblique photo series: Move the camera to ~80° (relative to vertical). Take 1 full rotation of photos, rotating the turntable ~10° between shots.Each circle should have 30–36 photos to ensure at least 60% image overlap.
2. Repeat for lower angles: Take additional image sets from:
3. 70–60°
4. 50–40°
5. 30–20°
6. 10–0°

Each angle adds depth and ensures the model captures all relevant detail.

With all your photos taken, it's time to turn them into a detailed 3D model using RealityCapture (RC). This step will calibrate the scene, scale it correctly using control points, and produce a mesh file ready for editing and machining.

🔄 Importing and Marker Detection:

1. Open RealityCapture and drag your photo folder into the workspace.
2. Go to the Inputs panel and confirm that all images have loaded.
3. In the Alignment tab, click Detect Markers.
4. In the right-hand panel, select the marker type:
5. Single Ring, 12-bit
6. Click Detect and wait for RC to identify the control points.

Once completed, uncheck Detect Markers to continue.

📏 Define Marker Distance (Scale the Scene):

1. Go to Scene 2D > Tools > Define Distance.
2. Open one of the zenithal (top-down) photos where all four markers are visible.
3. Click and drag from one marker to the adjacent one to draw a measurement line.
4. In the distance input box, type 0.12 m (assuming 12 cm between markers).
5. Repeat this process for each side of the square formed by the four markers.
6. When done, uncheck Define Distance to exit measurement mode.

🔧 Image Alignment and Ground Plane:

1. In the Alignment tab, click Align Images.
2. RC will now process the photos, detect camera positions, and align the point cloud.
3. This process may take several minutes depending on your hardware and image count.
4. After alignment, inspect the scene in 3D. To set the proper ground plane:
5. Go to Scene 3D > Tools > Set Ground Plane
6. Use the axis handles to adjust the floor orientation so the model sits flat.

✂️ Cropping and Mesh Generation:

1. You can either crop the model before or after mesh generation.
2. For now, we’ll crop before to speed things up and avoid unnecessary geometry.
3. Select the area of interest using the cropping box.
4. Go to Scene 3D > Mesh Model > Normal Detail to generate the mesh.
5. This process also takes a few minutes depending on your model’s complexity.

📤 Export the Mesh:

1. Once the mesh is created, go to the Export tab.
2. Choose Export Model > STL format (ideal for further editing and CNC prep).
3. Save it to your working folder.

✅ You now have a fully scaled, watertight 3D mesh of your negative mold — ready for cleanup or direct CAM processing.

Before machining the model, we’ll use Fusion 360 to clean up the geometry. This includes trimming excess surfaces and preparing the model for CAM by keeping only the sand imprint.

🔧 Set Workspace Units to Meters:

1. Open Fusion 360 and click the gear icon (Document Settings) in the browser panel.
2. Hover over Units, click the pencil icon, and select meters as the active unit.
3. Confirm and close.

📥 Insert the STL Model:

1. Go to INSERT > Insert Mesh.
2. Load the STL file exported from RealityCapture.
3. Position the mesh roughly in place and click OK.

🧱 Move the Model to Ground:

1. Open the SOLID > Move/Copy tool.
2. Use:
3. Right-click drag to rotate the model.
4. Scroll wheel to zoom.
5. ViewCube (top right) to orient the view.

Move the mesh so that the impression aligns with the workplane (ground level). Accept when aligned.

✂️ Trim Unnecessary Faces:

We’ll now cut away the outside of the model to keep only the sand impression.

1. Go to MESH > MODIFY > Plane Cut.
2. Select the mesh > Select the face you want to cut through.
3. Under Fill Type, choose No Fill.
4. Use the blue arrow and circular handle to adjust the cut direction.
5. Click OK to apply the cut.

Repeat this operation for all five outer sides, leaving only the top face for last.

🔄 Reposition and Final Cut:

Before trimming the top face, we’ll reposition the model to rest flat on the workplane. Use:

1. SOLID > Move/Copy again to adjust vertical position.
2. Ensure the model sits on the ground and measure the final Z-height, which will be used later in Easel.

Once repositioned:

1. Go back to MESH > MODIFY > Plane Cut.
2. Select and trim the top of the mesh as with the other sides.

💾 Save and Export:

1. Go to File > Save to keep the Fusion project.
2. Then, right-click the mesh in the browser and choose Save as STL.

✅ Now the model is clean, scaled, and ready for CAM operations in Easel or your preferred CNC software.

🧰 Materials You’ll Need:

1. 🖥️ CNC machine (We use Genmitsu 3020 Pro-Max)
2. 📏 Z-probe (Z-axis calibration probe)
3. 🔧 Vice or clamps to hold the acrylic sheet in place
4. 💠 Cast acrylic blocks
5. 🔩 Flat nose end mill 1/8" (3.175mm), single flute
6. 🔵 Ball nose 1/8 end mill 1mm cutting diameter, two flutes
7. 🧑‍💻 Easel Pro subscription

🛠️ Configure the Workspace in Easel

1. Select Material: Cast Acrylic.
2. Set your block dimensions (subtract bevel if your acrylic is angled).
3. Import your STL file via IMPORT > 3D STL, and uncheck auto-scale.

📐 Adjust the Model Parameters

1. Orientation: Top
2. Z-position: Base height - model height (to align model to top surface)
3. Cut Style: Model Boundary Relief
4. Cut Depth: Thickness of your acrylic
5. Padding: 0
6. Finishing Toolpath: Try 45° (gives a good finish in acrylic)

🔧 Toolpaths & Bit Settings

The process consists of two phases: roughing and finishing.

🪓 Roughing Pass:

1. Bit: Flat nose 1/8", single flute
2. Feed Rate: 800 mm/min
3. Depth per Pass: 0.5 mm
4. Spindle Speed: 9000 rpm

🎨 Finishing Pass:

1. Bit: Ball nose 1 mm, two flutes
2. Feed Rate: 400 mm/min
3. Spindle Speed: 6000 rpm

Generate toolpaths to preview time and results.

🧷 Mounting the Acrylic on the CNC

1. Use a vise or clamps.
2. Alternatively, apply painter’s tape to both the CNC bed and the acrylic, then glue them with cyanoacrylate.

🚀 Start the Milling Process

1. Install the roughing bit.
2. Move the bit to the bottom-left corner of the acrylic (flat face, not bevel).
3. Set XY zero.
4. Use the Z-probe to set the Z zero (or the paper method if not using a probe).

⚠️ Use a thin probe (like YoraHome Z-probe) to avoid tight clearances when using a vice.

1. Start the roughing cut.
2. When done, raise the Z-axis, change the bit, and use Work Zero to reset the CNC to its original origin.
3. Repeat Z-probing for the new bit.
4. Start the finishing pass: Monitor chips during the cut and vacuum carefully if needed to avoid melting.