Diode laser guide

Single Pass vs Multi-Pass Laser Cutting:
How Many Passes Do You Need?

For cutting 3mm plywood with a 10W diode laser and air assist, use 4–6 passes at 90% power and 250 mm/min — not one slow pass. Multiple passes deliver the same total energy more evenly, letting char clear between cuts and reducing edge burn. A 20W needs 2–3 passes for the same material; a 40W optical can often do it in 1–2. For engraving, one pass is almost always correct regardless of wattage.

By the numbers: A 10W diode laser needs 4–6 passes to cleanly cut 3mm plywood with air assist; without air assist that rises to 6–10 passes. A 40W optical laser cuts the same board in 1–2 passes. Engraving uses 1 pass at every wattage — Laser Tinkerer settings database, 115 rows, 2026-07-03.

How many passes does each wattage need? (The complete table)

These figures come from the Laser Tinkerer settings database (115 rows, aggregated from manufacturer specs and named community sources). "With AA" means air assist is active at typical cutting pressure (around 20 PSI or built-in pump).

All pass counts assume the recommended speed and power from the settings database. Source: Laser Tinkerer settings database v2.2, aggregated from manufacturer specifications and named community results. These are starting points — confirm with a test cut on your specific material batch.

Why does cutting wood need multiple passes when engraving only uses one?

The difference comes down to what you're asking the laser to do. When you engrave, the beam sweeps rapidly across a surface (at 2,000–8,000 mm/min) and each point only absorbs heat for a fraction of a second. The shallow ablation happens cleanly and the material cools immediately.

Cutting through material is a completely different physics problem. You're asking the beam to remove a column of material that could be 3mm, 5mm, or more deep. No diode laser can do that in a single moment — the beam only penetrates so far before the char layer beneath it starts absorbing energy and stops the beam from reaching fresh material.

Here's what actually happens on each pass:

The key insight is what happens at the bottom of the kerf between passes. After pass 1, there is a layer of char (carbonized wood). Char has much lower thermal conductivity than fresh wood — it absorbs heat and prevents the laser from penetrating further in the same pass. Between passes, that char can cool and, if you have air assist, get blown clear. Pass 2 then starts on slightly fresher material and can go deeper.

A single very slow pass tries to do all of this in one go. The result: intense local heating, thick char formation, and edge burn that looks dark and rough. The cut may not even be through — you've just created a very deep, very charred channel.

How does air assist change how many passes I need?

Air assist is the single biggest variable in pass count for cutting operations. It works in two ways:

1. Combustion gases: The cutting process generates CO₂ and water vapor that partially block the beam from reaching the bottom of the kerf. Air flow pushes those gases out before the next pulse arrives.
2. Char debris: Loose carbonized material accumulates in the kerf. A directed air stream at cutting pressure (20–30 PSI) physically clears that material, exposing fresh wood to each subsequent pass.

The practical result from our database: air assist typically reduces required cutting passes by about a third for wood materials. The exact numbers:

The reduction is less pronounced at 5W because even with perfect char clearing, a 5W beam simply doesn't have the energy density to penetrate quickly. See the full air assist guide for PSI settings and LightBurn configuration by material.

When is a single pass better for cutting?

Single pass is the right call in a few specific situations:

High-wattage machines

A 40W optical laser can often cut 3mm wood in a single pass at the right speed. The higher energy density means it can clear char fast enough within one traversal. If you're on a 40W and doing multiple passes on thin material, you may be going too slow — try increasing speed first.

Very thin or heat-sensitive materials

Materials that conduct heat poorly (cardboard, paper, thin foam, fabric, felt, thin leather) should always be cut in a single fast pass. With these materials, a second pass finds thermally compromised material and can cause fire, charring, or deformation. Go as fast as possible and accept one clean pass.

When you don't want charred edges at all

Multiple slow passes produce more cumulative char than one fast, optimized pass. If you're cutting a material where char is a serious concern (craft paper, thin balsa, thin cork), and you have a high-enough wattage machine, a single fast pass at very high power often gives cleaner edges than four slow passes. This is especially true when you mask the surface first.

Summary of when single pass wins

How multi-pass works with the Laser Tinkerer Energy Index

The Laser Tinkerer Energy Index (LTEI) describes energy delivery as:

LTEI = (power_% × optical_watts) ÷ speed_mm_min

This gives a value in J/mm — the energy delivered per millimetre of travel in a single pass. But the total energy that reaches the kerf across all passes is what determines whether you cut through:

Total energy = LTEI × number_of_passes

The insight from this model: you can reach the same total energy either by going slower (higher LTEI per pass) or by using more passes at a moderate LTEI. More passes at moderate LTEI is almost always better for cutting because:

• Lower peak temperature per pass = less thermal stress = less char
• Char clearing can happen between passes (either cooling naturally or via air assist)
• Each pass starts on slightly cooler, less carbonized material

For 3mm plywood on a 10W laser, the typical working LTEI per pass (0.90 × 10W ÷ 250 mm/min) is 0.036 J/mm. Multiplied by 5 passes, total delivered energy is around 0.18 J/mm of travel. Attempting a single pass to match that would require 50 mm/min at 90% — an extremely slow traverse that creates intense local heating and uneven char rather than a cleaner cut.

Common multi-pass mistakes to avoid

Starting with the wrong pass count

Don't guess — start with the settings database value for your machine wattage class and material, run a material test grid, and count passes from there. Guessing high wastes time; guessing low means you re-run the job and risk misalignment on the second attempt.

Moving the material between passes

This is the most common cause of a rough, doubled cut line. Set your passes in LightBurn (or LaserGRBL) before you start — let the software run all passes without moving the workpiece. Use clamps, masking tape, or a jig to prevent any movement during the cut. Even 0.1mm of shift creates a visible step in the kerf wall.

Using multi-pass for engraving

Adding a second engraving pass re-burns already-ablated material. The result is unpredictable darkening, rougher texture, and frequently a worse image than a single well-dialled pass. If your engraving is too light, increase power or slow down — don't add passes.

Forgetting to check focus at depth

On very thick materials (5mm+), the focal point becomes less accurate for later passes because the top of the material is where you focused, but the beam is now cutting near the bottom. Some users tilt the focus between passes for thick cutting. For 3mm and under, this is rarely an issue.

Same settings without air assist

If you normally run 4 passes with air assist and your pump is off or clogged, 4 passes won't get you through. Add 2–3 extra passes, or fix the air assist before cutting. See laser not cutting through for a diagnostic checklist.

Frequently asked questions

Settings on this page are calibrated starting points aggregated from manufacturer specs and named community sources, normalized using the Laser Tinkerer Energy Index. Always confirm with a test cut on your specific material. Operate at your own risk and follow your machine's safety manual. Methodology · Safety · Last verified 2026-07-03 · About