Phone Photo to CNC: The Complete Digital Slab Workflow

Step 1: Photograph the Slab

Stand approximately 1.5–2 meters from the slab and take a single photo that captures the entire surface. The photo does not need to be perfectly overhead — the calibration step corrects for perspective. What matters:

• The entire slab must be visible in the frame
• All four calibration targets must be visible
• Lighting should be even — avoid harsh shadows or glare spots
• If veins are faint, lightly wet the surface to increase contrast

Step 2–3: Place and Measure Calibration Targets

Place four calibration targets on the slab surface — one near each corner, inside the slab boundaries. Using a tape measure, record the distance from the center of each target to the center of every other target. You need a minimum of four measurements (the four sides of the quadrilateral formed by the targets).

Accuracy tip: This is the most important step in the entire workflow. The accuracy of your final DXF depends directly on the accuracy of these measurements. Measure carefully, to the nearest millimeter. Use a rigid tape measure, not a fabric tape. Double-check measurements that seem inconsistent.

The targets should be spread across the slab to provide good coverage. Avoid clustering them in one area — wider spacing gives better calibration accuracy across the full surface.

Step 4: Upload and Calibrate

Upload the slab photo to SlabKast. Mark the position of each target in the photo by clicking on its center point. Enter the measured distances between targets.

The software performs a mathematical rectification — it transforms the perspective-distorted phone photo into a true top-down, dimensionally accurate view. After calibration, every point on the slab image corresponds to a real-world coordinate. You can measure distances directly on the screen and they will match reality.

Step 5–6: Layout and Vein Match

Import your template pieces — the DXF or drawn shapes representing each piece of the countertop. Drag them onto the calibrated slab image. You can see immediately whether each piece fits within the slab boundaries and how the stone's natural veins flow through each shape.

For vein matching, rotate and flip pieces to align veins across seams. On marble, quartzite, and other veined materials, this step can take 5–15 minutes of careful adjustment. On uniform materials like engineered quartz, it takes seconds. If you are new to working without a scanner, the calibration step is the key to accuracy.

Plan seam locations based on both structural requirements and vein appearance. The software shows you exactly where each seam will fall and what the vein pattern will look like at each joint.

Step 7: Client Approval

Generate an approval link and send it to the client. They open it on their phone or computer and see the exact layout — their countertop pieces positioned on their specific slab, with the real vein patterns visible. No imagination required.

The client approves or requests changes. If they want adjustments — move a seam, try a different orientation, shift a piece to capture a specific vein — you make the change in the software and re-send. This iteration happens at zero cost. Changes after cutting cost thousands.

The approval is recorded with a timestamp. If there is ever a dispute about what was agreed upon, you have a documented record showing exactly what the client approved.

Step 8: Export DXF and Cut

Export the approved layout as a DXF file. The DXF contains all piece outlines positioned exactly as they appear on the slab, in millimeters at true scale. No scaling or rotation is needed.

On the CNC:

1. Place the slab on the CNC bed
2. Zero the machine to the calibration target positions on the physical slab
3. Verify alignment by jogging the CNC head to where other targets should be — if it lines up with the physical target, your zero is correct
4. Import the DXF into your CNC software
5. Set cutting parameters (tool diameter, feed rate, depth)
6. Cut

The pieces are cut in the exact positions shown in the approved layout. What the client approved is what gets fabricated.