How do you figure out depth per pass for relief/3D engraving in Lightburn?

how to figure out depth per pass for relief/3D engraving in LightBurn, focusing on MOPA fiber laser engraving on metals:

1. Understand the Concept

In LightBurn, depth per pass is not directly set in millimeters. Instead, depth is determined by a combination of:

• Laser power (%)

• Scan speed (mm/s)

• Material hardness and thickness

• Focus (spot size)

For MOPA fiber lasers, pulse frequency and pulse width also affect how much material is ablated per pass.

Conceptually:
Depth per pass ∝ (Power × Pulse Energy) / (Scan Speed × Material Hardness)

2. Use Grayscale Mapping

LightBurn handles 3D/relief engraving using grayscale images:

• White = 0% power → no engraving

• Black = 100% power → maximum power

Steps:

1. Import your 3D heightmap or grayscale image.

2. Open the Cut Settings Editor, choose “Mode = Image Mode” and “Scan”.

3. Set Max Power (%) to the desired intensity for the deepest areas.

4. Adjust Speed (mm/s) — slower speed = deeper engraving.

Tip: Start conservatively (lower power, higher speed) and test.

3. Test and Measure

Because depth depends on material and exact laser settings:

1. Run a small test patch (e.g., 10×10 mm).

2. Measure depth with a micrometer or digital caliper.

3. Adjust power or speed based on measured depth:

• Depth too shallow → increase power or reduce speed

• Depth too deep → reduce power or increase speed

On stainless steel with a 60W MOPA: typical single-pass depth ≈ 0.01–0.03 mm.

4. Adjust Passes

If the total desired depth exceeds what a single pass can achieve:

1. Use “Number of Passes” in LightBurn.

2. Total depth = depth per pass × number of passes.

3. Allow small delays between passes for metal cooling to prevent burning or discoloration.

5. Fine-Tune for Smooth Relief

• Slightly defocus the laser to spread energy and smooth gradient transitions.

• Use multiple passes with small depth per pass rather than trying to cut deep in one pass.

• For MOPA lasers, experiment with pulse frequency and pulse width if your controller exposes these options, as they can refine surface finish.