Deep Engraving
Going beyond surface marks into the metal, stamps, knife bolsters, signage, mold tooling, jewelry recesses. This is the technique that justifies a fiber laser over CO2 + spray.
The four knobs (mental model)
Every fiber engrave is a balance of four variables. Internalize this and the settings start making sense:
- Frequency = sandpaper grit. Lower freq = rougher, more aggressive material removal. Higher freq = finer, smoother finish.
- Power = pressure. How hard you push.
- Speed = travel rate. How fast you move across the part.
- Pulse width = dwell. How long each pulse heats the spot. Long pulse = more heat per pulse = deeper bite. Short pulse = clean ablation, no heat-affected zone.
For deep engraving you want: low freq + max power + slow speed + 200ns pulse, maximum energy per pulse, plenty of overlap.
The verified 3-pass formula
This is the community-proven formula for a typical 60W MOPA. Scale per your actual wattage using the Power Scaling Rule (Foundations → Understanding Frequency). Two aggressive material-removal passes followed by a clean-up pass.
| Pass | Speed | Power | Freq | Pulse | Loops | Line | Hatch angle |
|---|---|---|---|---|---|---|---|
| 1, material removal | 1500 | 100% | 35 kHz | 200 ns | 15-20 | 0.02 | 0° |
| 2, perpendicular | 1500 | 100% | 35 kHz | 200 ns | 15-20 | 0.02 | 90° |
| 3, clean-up / floor at 45° | 2000 | 100% | 75 kHz | 100 ns | 5 | 0.02 | 45° |
Speed in mm/s. Loops = passes within that layer. The 30W version of this formula uses 25 loops on passes 1 and 2; with 60W you can drop to 15-20 and get the same depth in less time.
By material (60W, 70mm/150mm)
| Material | Depth/minute (typical) | Adjustment |
|---|---|---|
| Stainless 304/316 | 0.08-0.12 mm/min | Use formula as-is. Cleanest results. |
| Mild / carbon steel | 0.12-0.20 mm/min | Lower freq to 30 kHz, run formula. |
| Brass (260, 360, 385) | 0.06-0.10 mm/min | Reflective, scuff first with Scotch-Brite. Same formula. |
| Aluminum 6061/7075 | 0.10-0.18 mm/min | Tons of slag; air assist mandatory. Run formula at speed 1000. |
| Hardened tool steel | 0.05-0.08 mm/min | Slower. Drop loops by half, run more cycles. |
| Titanium grade 2/5 | 0.05-0.10 mm/min | Burns easily. Drop power 10%, freq 50 kHz. |
Hatch angle rotation
If every pass uses the same hatch angle, you carve grooves into the floor and the surface looks corrugated. Rotation breaks that up. Use the 90° / 180° / 315° pattern from the formula, or for very deep work rotate 30-45° per pass through 8 passes.
Z-stepping (refocus per pass)
As material is removed, the part surface drops below the lens's focal point. By pass 5 of a deep engrave, you're firing into out-of-focus space, energy density drops, depth slows.
In Lightburn galvo: layer settings → Z step per pass: 0.05-0.10 mm. Lightburn drops the head between passes, keeping the beam focused on the working floor of the cavity.
- Stainless: Z-step 0.05 mm/pass
- Aluminum / brass: Z-step 0.08-0.10 mm/pass (faster removal)
- Coin relief work: Z-step 0.02-0.03 mm, finer because depth is shallower
Wall sharpness: the perimeter trick
Hatch fill alone leaves soft, sloped cavity walls (each row of dots tapers off at the edge). To get vertical walls, add a perimeter outline pass between every 5 hatch passes.
- Outline pass: Speed 200 mm/s, Power 100%, Freq 30 kHz, Pulse 200 ns, 3 loops along the path.
- Set the perimeter as a Line layer above the hatch Fill layer in Lightburn.
Air assist
Stock OMTech 60W MOPAs ship without head-mounted air assist. Adding it for deep engraving is the single best upgrade. A small oil-less compressor at 30-50 psi through a 6mm coaxial nozzle:
- Clears vaporized metal before it re-deposits as slag.
- Cools the part, reduces heat-affected discoloration outside the cavity.
- Cuts engrave time by ~25% on aluminum and brass.