CNC Stone Engraving Guide

Machine Specifications

Material Selection & Sourcing

Best Materials for Your 17.5" × 17.5" Bed

✓ Recommended Materials

• Granite/Marble Tiles (12"×12" or 16"×16" floor tiles) - Available at Home Depot, Lowe's, flooring stores. Flat, uniform thickness, affordable
• Marble Slabs (bathroom vanity offcuts) - Stone yards, countertop fabricators offer scrap pieces. Usually 3/4" thick, very flat
• Travertine Tiles - Softer stone, easier to cut than granite
• Slate Tiles - ONLY if single-layer, avoid laminated varieties

✗ Materials to Avoid

• Organic/river rocks (impossible to stabilize)
• Layered slate (delaminates, breaks diamond bits)
• Material thicker than 1.5" (limits Z-clearance)
• Rounded or irregular shapes

Sourcing Challenges Learned

Finding suitable material for the bed size was difficult. Organic rock shapes were nearly impossible to stabilize properly. The best solution proved to be commercial tiles and slabs from home improvement stores and stone yards.

Section 2: Work Holding for Water Submersion

Traditional clamps, tape, and fixtures don't work underwater. Here are proven solutions based on testing multiple methods.

Method 1: Marine Silicone Adhesive (Best for Flat Tiles)

Materials Needed

• Marine-grade silicone adhesive OR aquarium-safe silicone
• Sacrificial base board (plastic cutting board, HDPE, acrylic)
• 24 hours cure time

Steps

1. Clean stone surface with isopropyl alcohol
2. Apply thick bead of silicone to base board
3. Press stone firmly, ensuring no air pockets
4. Weight it down, let cure 24 hours fully submerged
5. After engraving, pry off with putty knife
6. Remove residual silicone with razor blade

Method 2: Mechanical Clamping with Water Barrier

Materials Needed

• T-track clamps or adjustable cam clamps
• Neoprene/rubber padding
• Waterproof clamp extensions (PVC pipe or aluminum)

Steps

1. Mount T-tracks to wasteboard edges
2. Position stone centered
3. Use rubber-padded clamps at 4 corners
4. Ensure clamps clear tool path (check in CAM software)
5. Tighten firmly but don't crack stone

Failed Methods (Learn from These)

Section 3: Water Containment System

Simple Water Tray Setup

Option A: Raised Reservoir

1. Build sides around bed using:
   • Foamcore board sealed with silicone
   • Plastic storage bin (cut to fit around machine)
   • Acrylic sheets sealed with aquarium silicone
2. Water depth: 0.5" - 1" above material surface
3. Add small aquarium pump for circulation (prevents sediment buildup)

Option B: Flooded Pocket

• Machine a pocket in wasteboard
• Line with pond liner or thick plastic sheeting
• Seal edges with waterproof tape
• Keep water level just above stone surface

Water Management Tips

• Change water frequently (every 2-3 cuts)
• Strain out stone particles
• Add drop of dish soap to reduce surface tension

Section 4: Design Considerations for Stone

Scale Matters

• Features smaller than 2mm may not cut cleanly in stone
• Line thickness: Minimum 1mm for V-carving, 2mm for profiling
• Detail level: Stone is less forgiving than wood—simplify designs

Relief Depth Guidelines

• Maximum practical depth: 3-5mm in granite/marble
• Typical depth: 1-2mm for detailed work
• Test shallow first!

Section 5: Creating Toolpaths in Fusion 360

Step 1: Design Your Model

1. Create or import your design in Fusion 360
2. Keep it 2D or shallow 2.5D (relief)
3. If starting from 2D: File → Export → DXF

Step 2: Switch to Manufacturing Workspace

1. Click Design dropdown → Select Manufacture
2. Click Setup → New Setup

Step 3: Configure Setup

Step 4: Create Tool (Diamond Bit)

Click Tool Library → New Tool

For V-Bit Diamond:

Type: Chamfer Mill
Diameter: (your bit diameter, typically 6mm or 1/4")
Tip Angle: (60°, 90°, or 120° - measure yours!)
Shoulder Length: (measure cutting depth)
Flute Length: (measure)

Cutting Parameters:
  Spindle Speed: 8,000 - 12,000 RPM
  Feed Rate: 100-300 mm/min (START SLOW!)
  Plunge Rate: 50-100 mm/min

For Flat Diamond Bit:

Type: Flat End Mill
Diameter: (your bit diameter)
Flute Length: (measure)

Cutting Parameters:
  Spindle Speed: 8,000 - 12,000 RPM
  Feed Rate: 150-400 mm/min
  Plunge Rate: 75-150 mm/min

Step 5: Create Toolpath Operations

For Engraving/V-Carving:

1. Select 2D → Engrave
2. Select geometry (curves, text, etc.)
3. Tool: Your diamond V-bit
4. Depths:
   • Bottom Height: -1mm to -3mm (start shallow!)
   • Top Height: 0
5. Passes: Maximum Stepdown: 0.25mm - 0.5mm
6. DO NOT enable "Stock to Leave"

For Pocket/Relief:

1. Select 2D → Adaptive Clearing OR 2D → Pocket
2. Select pocket boundary
3. Tool: Flat diamond bit
4. Depths: Bottom Height: -2mm (start shallow)
5. Passes:
   • Optimal Load: 0.25mm - 0.5mm (for adaptive)
   • Stepover: 40-50% of bit diameter
6. Critical: Stock to Leave = 0mm (radial and axial)

For Profiling/Cutout:

1. Select 2D → Contour
2. Select edges
3. Side: Outside/Inside as needed
4. Multiple Depths: 0.5mm stepdown
5. Stock to Leave: 0mm

Step 6: Simulate Toolpath

1. Click Simulate button
2. Verify toolpath covers all geometry
3. Check for collisions with clamps
4. Verify Z-clearance (1" minimum)

Step 7: Post-Process to GRBL

1. Select your toolpath in browser
2. Click Post Process
3. Post Configuration: Select grbl / grbl
4. Output File: Choose location, name it clearly
5. Click Post
6. File will be .nc or .gcode format

Section 6: Creating Toolpaths in FreeCAD

Step 1: Design in Part Design Workbench

1. Open FreeCAD, create new document
2. Workbench dropdown → Part Design
3. Create sketch or import DXF
4. Pad/extrude to create 3D model

Step 2: Switch to Path Workbench

1. Workbench dropdown → Path
2. Path tools appear in toolbar

Step 3: Create Job

1. Click Job icon (or Path → Job)
2. Setup Tab:
   • Operation: 3D Surface or Profile/Pocket
   • Stock: From base, add 0mm offset
   • Click "Set Origin" → Select reference point

Step 4: Create Tool

1. Click Tool icon (or Path → Tool)
2. Tool Controller Manager opens
3. Click New Tool

Diamond V-Bit Settings:

Shape: V-Bit
Tip Diameter: 0.5mm (point)
Diameter: 6mm (your actual diameter)
Angle: 60/90/120° (measure)
Cutting Edge Height: Your flute length

Feeds & Speeds:
  Spindle Speed: 10,000 RPM
  Horizontal Feed: 200 mm/min
  Vertical Feed: 100 mm/min

Step 5: Create Operations

For Engraving:

1. Path → Engrave
2. Base Geometry: Select your sketch/edge
3. Tool Controller: Your diamond bit
4. Depths: Start Depth: 0mm, Final Depth: -1mm to -3mm
5. Step Down: 0.5mm

For Pocketing:

1. Path → Pocket Shape
2. Base Geometry: Select pocket face
3. Tool Controller: Your flat bit
4. Depths: Final Depth: -2mm
5. Step Over: 50% of diameter
6. Important: Stock to Leave: 0mm

For Profile Cut:

1. Path → Profile
2. Base Geometry: Select edges
3. Side: Outside/Inside
4. Depths: Final Depth: -5mm (through material)
5. Multiple Passes: Step Down: 0.5mm

Step 6: Post-Process

1. Select "Job" in tree
2. Click Post Process icon
3. Post Processor: Select grbl_post
4. Click OK
5. Save .nc or .gcode file

Section 7: Running Jobs in Universal G-Code Sender

Step 1: Connect to Machine

1. Launch Universal G-Code Sender
2. Connect settings:
   • Port: (select your USB connection)
   • Baud: 115200
   • Firmware: GRBL
3. Click Connect

Step 2: Home the Machine (If Available)

• If you have limit switches: Click $H or type $H and press enter
• Machine moves to home position
• If no limit switches, skip this step

Step 3: Load Your G-Code

1. File → Open (or click folder icon)
2. Navigate to your .nc/.gcode file
3. File loads, visualizer shows toolpath

Step 4: Install Diamond Bit

1. Install diamond bit in collet
2. Tighten securely
3. Measure your bit length (write it down!)

Step 5: Position Material

1. Secure stone using your chosen method
2. Fill water to 0.5"-1" above stone surface
3. Check clamps don't interfere with toolpath

Step 6: Zero the Machine (CRITICAL!)

X and Y Zero (Work Position)

Method A: Corner Touch-Off

1. Jog machine using control panel in UGS (keyboard shortcuts or click arrows)
2. Position bit above corner of your design area
3. Lower Z until bit is ~5mm above material
4. Jog X and Y to align bit tip with corner
5. Set Zero:
   • Type in console: G10 L20 P1 X0 Y0
   • OR click Reset Zero → X and Y

Method B: Center Touch-Off

1. Jog to center of material
2. Align bit tip with center point
3. Set X0 Y0 as above

Z Zero (Height/Depth Reference) - THE CRITICAL ONE

Option 1: Paper Method (Simple)

1. Jog X/Y to location over material (avoid clamps)
2. Place thin paper on stone surface
3. Slowly jog Z down in small increments (0.1mm)
4. When bit just touches paper (you feel slight drag when pulling paper)
5. Raise Z by 0.1mm (thickness of paper)
6. Set Z Zero:
   • Type: G10 L20 P1 Z0
   • OR click Reset Zero → Z

Option 2: Touch Plate Method (If Available)

1. Place touch plate on material
2. Clip ground to bit
3. Use UGS probe function
4. Enter plate thickness
5. Machine automatically finds Z zero

Verify Zero Position

1. After setting zero, jog up in Z (5-10mm)
2. Jog to X0 Y0
3. Slowly jog to Z0
4. Bit should return exactly to surface
5. If not, re-zero!

Step 7: Air Pass Test (Dry Run)

1. Raise Z by 10mm (jog up or offset)
2. Click Visualize to see toolpath
3. Click Send or Run
4. Watch machine trace path above material
5. Check for:
   • Clamp collisions
   • Travel outside safe area
   • Strange movements
6. Stop immediately if issues!

Step 8: Final Pre-Flight Checklist

• Water level covers material
• Bit is tight in collet
• Clamps don't interfere
• Z zero is set correctly
• Emergency stop is accessible
• Eye protection on

Step 9: Run the Job

1. Return to Z zero (jog to X0 Y0 Z0)
2. Click Send or Run
3. Watch the first pass closely!
   • First cut should be shallow
   • Stop if bit is too deep or shallow
   • Adjust Z zero if needed
4. Monitor for:
   • Bit vibration (too fast)
   • Stone cracking (too aggressive)
   • Water splashing (add more)
   • Strange sounds (STOP!)

Step 10: Post-Cut

1. Let machine finish, return to safe position
2. Remove stone carefully
3. Rinse stone clean
4. Dry completely
5. Inspect engraving
6. Clean machine and change water

Section 8: Diamond Bit Care & Maintenance

Types of Diamond Bits

• V-bit: Engraving, lettering, fine detail
• Flat end mill: Pocketing, surfacing, general cutting
• Ball nose: 3D reliefs, smooth curves

Lifespan & Wear

• Diamond bits last 10-50x longer than carbide in stone
• Signs of wear: Slower cutting, rough finish, squealing noise
• Cost: $15-50 per bit (worth the investment!)

Maintenance Tips

• Rinse clean after each use
• Inspect for damaged diamonds under magnification
• Store in protective case
• Never drop them!

Where to Buy

• Amazon: Search "CNC diamond engraving bits"
• AliExpress: Cheaper options, longer shipping
• CNC specialty stores: Router Bit World, Whiteside

Section 9: Troubleshooting

Toolpath Issues

Problem: Adaptive clearing leaves gaps at small scale

Solution:

• Use "Pocket" operation instead of Adaptive Clearing
• Set stock to leave to 0mm
• Reduce optimal load to 0.1-0.25mm

Problem: V-carving too shallow or deep

Solution:

• Measure your bit angle accurately
• Adjust "Bottom Height" in engrave operation
• Test on scrap material first

Work Holding Issues

Problem: Stone vibrates during cut

Solutions:

• Apply more clamping pressure
• Use silicone adhesive method instead
• Reduce feed rate by 50%
• Reduce depth of cut to 0.25mm per pass
• Check machine rigidity (tighten all bolts)

Problem: Diamond bit breaks

Solutions:

• Never cut layered slate
• Reduce feed rate significantly
• Reduce depth per pass to 0.25mm
• Ensure material is completely stable
• Check for cracks in material before cutting

Cut Quality Issues

Problem: Rough or chipped edges

Solutions:

• Slow feed rate
• Increase spindle RPM
• Replace worn bit (diamonds wear out)
• Better material stabilization
• Water level too low (add more water)

Problem: Bit wanders, not cutting straight

Solutions:

• Z zero is incorrect (re-zero carefully)
• Material not flat (surface it first)
• Machine not rigid enough (tighten everything)
• Feed rate too fast for material

Quick Reference Card

Spindle Speed: 10,000 RPM
Feed Rate: 150-200 mm/min
Plunge Rate: 75-100 mm/min
Depth per Pass: 0.25-0.5mm
Total Depth: 1-2mm for details, 3-5mm maximum

Sample Beginner Project

Simple Name Engraving

Project Steps

1. Design name in Fusion 360 (2D text sketch)
2. Create Manufacture → Engrave operation
3. Set depth: -1mm, step down: 0.5mm
4. Post-process to GRBL format
5. Secure tile with silicone adhesive (day before)
6. Submerge in water
7. Zero machine carefully following procedure
8. Run at 150mm/min feed rate