How the Diode Laser Settings Calculator Works
A laser mark depends mostly on how much light energy lands on each millimetre of the line, so doubling the power lets you go roughly twice as fast for the same mark. This tool keeps a table of typical starting points for a 10 W optical blue diode and scales them to your laser and machine.
Every value here is a rule of thumb gathered from common community and maker starting points. Wood batches, glue, coatings, focus, air assist and the laser module itself all change the result. The material test grid is the real answer: burn it on an offcut of the exact material you are using.
The Method
1. Line energy scaling (engraving)
energy per mm ∝ W × power% ÷ speed
speed = speed₁₀ × W ÷ 10 (same power %)
W is your optical power. A 20 W laser at the same power % moves twice as fast as the 10 W reference; a 5 W at half the speed.
2. Machine speed cap
if speed > max: speed = max,
power% = power%₁₀ × max ÷ (speed₁₀ × W ÷ 10)
When the machine cannot go fast enough, the power is lowered instead so the energy per mm stays the same. Below about 10 % some diodes fire unevenly.
3. Cutting passes
E₁₀(t) = passes ÷ speed (10 W reference, interpolated in thickness t)
E = E₁₀ × 10 ÷ W, passes = max(1, round(E × v_pref)), speed = passes ÷ E
Cuts are always at 100 % power. v_pref is the speed the 10 W reference uses (for example 350 mm/min for 3 mm plywood), so passes go up as power goes down. Real lasers below 10 W usually do a bit worse than this.
4. S value and line interval
S = round(power% ÷ 100 × $30)
LPI = 25.4 ÷ line interval (mm)
LightBurn and LaserGRBL work in %, raw G-code in S. With $30=1000, 30 % is S300. A 0.1 mm interval is 254 LPI, 0.08 mm is about 318 LPI.
Worked Example
20 W optical diode on a 6000 mm/min gantry, $30=1000, basswood and 3 mm plywood
- Basswood engrave reference at 10 W: 6000 mm/min at 30 %. Scaled: 6000 × 20 ÷ 10 = 12000 mm/min, which is above the 6000 mm/min machine limit.
- Capped: speed 6000 mm/min, power 30 × 6000 ÷ 12000 = 15 %, which is S150. Line interval 0.1 mm (254 LPI).
- 3 mm plywood reference at 10 W: 2 passes at 350 mm/min, so E₁₀ = 2 ÷ 350 = 0.00571. At 20 W: E = 0.00571 × 10 ÷ 20 = 0.00286; passes = round(0.00286 × 350) = 1; speed = 1 ÷ 0.00286 = 350 mm/min, 1 pass, 100 %.
- Test grid: 5 × 5 squares of 5 mm with 2 mm gaps is 33 × 33 mm. At a 0.1 mm interval each square is 51 lines of 5 mm = 255 mm of burn. At 1000 to 5000 mm/min in 1000 steps the burn time is 5 rows × 255 × (1/1000 + 1/2000 + 1/3000 + 1/4000 + 1/5000) = 2.9 minutes, plus travel and acceleration.
How to Read the Test Grid
- Look for the fastest square that gives the mark you want. Faster settings char less and finish sooner. Find the darkest acceptable square without a brown halo or a melted edge.
- Check across the diagonal. Squares with about the same power ÷ speed should look similar. If high-speed squares are much lighter than the rule predicts, the machine may not be reaching that speed (acceleration) on such small squares.
- Wipe it before judging. Brush off soot from wood and slate. Slate and anodised aluminium often look different after a wipe with a damp cloth.
- Photo engraving needs a lighter setting than solid fills. Pick a square slightly lighter than your ideal solid black, because dithered dots spread.
- Note it down. Write the winning setting on the back of the test piece and keep it with the material stock.
Troubleshooting
| Problem | What to try |
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Practical Tips
- Focus first. Most diode modules come with a focus gauge or a fixed-focus spacer; a laser out of focus by 1 mm can halve the mark. For thick cuts, some people focus slightly into the material, about a third of the thickness.
- Air assist: strong for cutting (it clears smoke, cools the edge and stops flare-ups); light or off for engraving, where strong air can blow soot over the work.
- Line interval: 0.08 to 0.1 mm suits most diode spots. Smaller intervals overlap and darken the fill (and take longer); larger intervals leave stripes.
- Mask it. Paper application tape over wood stops smoke staining around the engraving.
- Need artwork? Trace an image with the Image to DXF Converter, draw shapes in the DXF Sketcher or DXF Part Maker, and price cut jobs with the DXF Cut Cost estimator. To turn a photo straight into raster G-code, use Image to Laser G-code.
More Laser & CNC Tools
- G-code Viewer: preview the test grid toolpath before you burn it.
- Image to Laser G-code and Image to DXF Converter
- DXF Sketcher, DXF Part Maker and DXF Cut Cost
- Milling metal rather than burning wood? The feeds and speeds calculator covers spindle RPM and chip load for CNC routers and mills.
Frequently Asked Questions
A typical starting point on a 10 W optical diode is about 3000 mm/min at 50 % power with a 0.08 mm line interval; a 5 W laser needs about half that speed. Slate turns light grey where it is lasered. Natural slate varies, so burn a test grid on the back of one coaster first, and wipe on a little oil afterwards for more contrast.
Blue diode light (about 450 nm) passes straight through clear acrylic, and white, light blue and many pale colours reflect or transmit it too, so almost no energy is absorbed. Black or dark opaque cast acrylic absorbs it and engraves well. For clear acrylic you need a CO2 laser, or you can engrave through a dark paint or masking layer on the surface.
Many diode lasers are sold by electrical input power, not light output. A "40 W" class laser is usually about 5 to 10 W optical, roughly an eighth to a quarter of the advertised figure. Look for "optical output power" in the module's specifications and enter that number here, because the settings scale with optical power.
A common starting point is 100 % power at about 350 mm/min with 2 passes, air assist on and the laser focused on the surface. The glue layers are what slow a diode down, so laser-grade plywood cuts far more reliably than hardware-store ply. Check the cut after each pass and add one more if it is not through.
Line interval is the distance between the back-and-forth lines the laser burns to fill an area. LightBurn calls it line interval and also shows it as lines per inch (LPI = 25.4 ÷ interval in mm). For most diode lasers 0.08 to 0.1 mm (about 250 to 320 LPI) fills solidly without wasting time.
All speeds, powers, passes and thicknesses are typical starting points and rules of thumb for blue 445 to 455 nm diode lasers, not tested data for your machine or material. Always burn a test grid on a scrap of the same material, stay with the machine and follow your laser maker's safety instructions. LightBurn also has a built-in material test tool if you use it.