CO2 Deep Engraving: Wood & Acrylic

CO2 deep engraving is fundamentally different from fiber. Where fiber ablates metal in microns, CO2 burns/vaporizes wood and acrylic in millimeters per pass. The technique: multi-pass with reducing power per pass, plus careful Z management on thicker stock.

Wood relief (the headline use case)

Two approaches:

• Vector outline + bottom fill: for plaque-style work with a clear outline. Engrave the outline first (Line layer), then fill the recessed area (Fill or Image).
• Grayscale image (depth-mapped): for sculptural relief from a depth map. See 3D Engraving, STL & Grayscale for the full workflow.

Multi-pass deep wood engrave

Single-pass grayscale gives subtle relief (~0.5-1mm depth). For dramatic 2-4mm depth in maple, cherry, or walnut:

1. Pass 1: full power: speed 350 mm/s, power 30%, line interval 0.06mm. Establishes initial depth profile.
2. Pass 2: drop power 5%: 350 mm/s, 25%, same interval. Deepens highlights, leaves dark zones lighter.
3. Pass 3: drop another 5%: 350 mm/s, 20%. Continues deepening.
4. Pass 4-5 if more depth needed: drop another 5% per pass.
5. Optional final inverted pass: flip Negative Image, run at low power. "Burnishes" surface for character/weathered look.

Total time: 4-6× single-pass. Result: dramatic relief that reads as 3D from a few feet away.

Acrylic deep relief

Cast acrylic engraves to a frosted finish. Multi-pass at the same Z gives 0.3-0.8mm relief:

• Speed 400 mm/s, power 25-30%, line interval 0.06mm.
• 3-5 passes for visible depth.
• Air assist at minimum, just enough flow to keep the lens clean; high air rounds off the relief edges.
• Reverse-engraved (mirrored) on the back of clear acrylic = "lit edge" sign with LED panel behind.

Z-stepping for very deep relief

For 5mm+ relief in wood, refocus between passes. Lightburn → Layer Settings (Advanced) → Z Step per Pass: 0.5-1.0 mm.

Without Z-stepping, by pass 5 your beam is firing into out-of-focus space, depth stalls.

Stamp making (rubber + delrin)

Reverse-image, deep-engrave the substrate to leave the design raised. Settings:

• Laser-grade rubber stamp blank: 400 mm/s, 50% power, 0.05 line, 2-3 passes for ~1mm depth.
• Delrin / acetal: 200 mm/s, 70%, 0.05 line, 2 passes.
• Image mode: Threshold (sharp edges) or Grayscale for ramped shadow stamps.

Inlay technique

Cut a pocket in one wood, cut a matching shape in a contrasting wood, glue the inlay into the pocket. CO2 makes this easy:

1. Design the inlay shape as a vector path.
2. Cut the pocket: same vector, kerf-compensated inward by about half your kerf (0.05-0.1mm), so the burn opens the hole to the design size.
3. Cut the inlay: same vector, kerf-compensated outward by the same amount. See Inlay Technique for the diagram.
4. Glue (Titebond III for hardwoods), clamp, sand flush after dry.

Common pairings: walnut on maple, padauk on poplar, ebony on birch.

Common pitfalls

• Burnt edges from too-slow speed. Drop speed slightly, increase passes instead.
• Loss of detail at depth. Tonal range compressed in source image, re-stretch in Photoshop.
• Wavy floor. Air assist too high (blowing the edge during cut), or material warped, flatten with magnets/weights.
• Acrylic relief looks bumpy. Air assist too high. Drop pressure or turn it off entirely.

3D grayscale relief on CO2: full walkthrough

Grayscale (also called 3D relief or grayscale engraving) modulates the laser power based on the shades of gray in your source image. White = min power, black = max power, and everything in between ramps proportionally. On softer materials, that produces actual physical depth, a true 3D relief, not just a shaded image.

1. Find a depth-map / grayscale source

• Search "STL grayscale [subject]", there are well-known community files floating around (the bee-with-honeycomb relief image is a classic example).
• Bigger source = more data for the laser. Aim for ≥570px wide; upscale in Photoshop if you need to. STL files exported as a depth pass via Blender or Aspire give the cleanest input.
• For AI-generated source images. See Relief Coin Engraving, same prompts and tools (Midjourney with "bas relief" + SculptOK / tiling-zoedepth Colab) work for CO2 grayscale too.

2. Photoshop prep: light touch only

• Don't strip the background. The gradient IS the design, there's no "subject vs background."
• Brightness / contrast: leave alone or only nudge for cleanup. Heavy contrast adjustments break the gradient.
• Sharpen → Smart Sharpen for edge detail, but don't overdo it, too much sharpening creates hot spots that show as banded depth changes.
• Image Size: scale to your final part dimensions (e.g., 4×4" or 5×5") at ~400 DPI so Lightburn has dense data to work with.
• Export as PNG.

3. Lightburn settings

Double-click the image layer to open settings:

Setting	Value	Why
Image mode	Grayscale	NOT dither, NOT threshold. Grayscale modulates power per-pixel.
DPI	~300 with a 1.5" lens on 100W	Higher-res lenses (HR / 2") can push to 333+; wider 3"/4" lenses drop to ~254.
Speed	8-12 in/sec (200-300 mm/s)	Slower = better gradient fidelity. Going too fast asks the tube to modulate faster than it can keep up.
Max power	~26% on 100W (first pass)	Bump to ~38% for a deeper second pass. Don't go full power on a single pass, you'll char before you have depth.
Min power	Your tube's turn-on threshold (6-8% on most CO2)	Prevents the lightest grays from firing the tube at all and washing out highlights. Critical setting, if min power is 0, the lightest areas still fire weakly and the highlights smudge.
Scan angle	180°	Starts from the top of the image, faces and key features come out first, so you can abort early if the test piece is going badly.
Negative image	OFF for engraving INTO wood	Dark areas of the source = deepest cut. Flip to ON for acrylic where you want lights to be the deepest cuts.

4. Multi-pass strategy

For more depth, two passes at moderate power beats one pass at max power: cleaner edges, less charring, better gradient. On acrylic especially, multiple light passes outperform a single hot pass. A typical sequence on 100W: pass 1 at 26% max / 7% min, pass 2 at 38% max / 7% min, keeps the gradient intact while doubling depth.

5. Material notes

• MDF: best proof-of-concept material. Cheap, no grain to fight, takes depth uniformly. Ideal for testing settings before committing to a final piece.
• Softer hardwoods (basswood, alder): work well IF grain is minimal. Heavy-grain woods (oak, walnut burl) compete with the image and the grain dominates over the depth.
• Cast acrylic: works for 3D effect but use multiple light passes. Extruded melts and won't hold detail.

6. Watch for "curtaining"

If you see vertical-line artifacts in the finished engrave, two possible causes: (a) speed too slow (the tube's modulation can't track the slow gradient. Drop power or bump speed), or (b) mechanical (belt tension, gantry play, or skipping steps). Test on MDF first to isolate which.

7. Finishing

After the engrave, lightly sand with an orbital sander on low speed with fine grit. The contrast between sanded high points (clean wood) and untouched depths (charred dark) is what makes the 3D effect read in person. Don't sand hard, you'll lose the relief.

For STL → depth map workflow and AI-assisted depth-map generation. See Relief Coin Engraving in the Fiber section. Same source files; CO2 uses Grayscale image mode while fiber galvo uses 3D Sliced for the same input.