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How to run a laser material test grid (and actually read the result)
Every settings chart on the internet, including ours, is a starting point. A test grid is how you turn a starting point into your numbers — for your machine, your lens, your sheet. It takes about ten minutes and it is the single highest-value habit in laser work.
Price a job once you have your settings →Why a chart can only get you close
Two identical machines cutting the same nominal material will not want the same settings. What moves the numbers, roughly in order of impact:
- Focus — set for the exact thickness. An out-of-focus beam is a wide, weak beam.
- Air assist — on wood it changes the result more than most setting tweaks.
- Material batch — plywood glue lines, moisture and veneer colour all change how much power reaches the bottom of the kerf. Cast and extruded acrylic behave differently too.
- Optics — a lens with a film of resin on it can cost you a third of your power.
- Age — CO2 tubes and diodes both fall off over their life. A three-year-old tube does not cut like the chart it shipped with.
None of these are visible in a table. All of them show up in a grid.
The ten-minute version
- Take an offcut of the same sheet you will cut the job from.
- Focus for that exact thickness.
- Generate a 5×5 grid of 15 mm squares — speed on one axis, power on the other.
- Bracket a known starting point: about half to double the speed, and a power band around it.
- Run it with the air assist you will use on the real job.
- Push the squares out from the back and pick the fastest, coolest one that releases cleanly.
- Write it down. A setting you cannot find again is a setting you do not have.
Where to generate the grid
LightBurn
Built in: Laser Tools → Material Test. Set the axes to Speed and Power, choose your min and max for each, and set the grid to 5×5. It generates the squares and the labels together, which is the part that matters — an unlabelled grid is a puzzle by the time it finishes.
xTool Creative Space
No built-in generator. Draw a row of rectangles, then set power and speed per object — XCS lets you give each object its own parameters. Tedious once, reusable forever if you save the file.
LaserGRBL
Free test-grid templates are widely available for GRBL machines, or use the built-in engraving test pattern. Check the file's units before running it — most templates are written in mm/min, and a template meant for a 20 W diode will simply stall a 5 W one.
What ranges to test, by machine class
These are the brackets we would set for a cut grid on 3 mm plywood. Centre the grid on the middle of the range, and if every square cuts through, your range was too slow — retest faster.
| Machine class | Material | Speed range | Power range | Passes | Note |
|---|---|---|---|---|---|
| 5-10 W diode | 3 mm plywood | 120-260 mm/min | 80-100% | 2-4 | Slowest class - expect passes. 6 mm ply is not realistic. |
| 20 W diode | 3 mm plywood | 200-450 mm/min | 80-100% | 1-2 | One pass is achievable on good ply. |
| 40 W diode | 3 mm plywood | 400-900 mm/min | 80-100% | 1-2 | Opaque acrylic only - never clear. |
| 40-45 W CO2 | 3 mm plywood | 8-18 mm/s | 55-85% | 1 | K40 / Glowforge class. Cuts clear acrylic. |
| 55-60 W CO2 | 3 mm plywood | 10-24 mm/s | 50-80% | 1 | Sweet spot for most small shops. |
| 80-100 W CO2 | 3 mm plywood | 14-30 mm/s | 40-70% | 1 | Too much power scorches thin stock - go faster, not hotter. |
Units trap: diode machines are usually set in mm/min and CO2 in mm/s. 600 mm/min is 10 mm/s. Mixing the two is the most common reason a "tested" setting does nothing at all.
A cut grid and an engrave grid are different tests
Cut test
You are looking for release, not darkness. Push each square out from the back with light thumb pressure. The winner is the fastest, lowest-power square that comes out cleanly with no charring on the back face. A square with a beautiful dark edge is usually a square you burned too long.
Engrave test
You are trading contrast against detail and time. Run the grid at the line interval you actually intend to use, because interval changes both the look and the job time. Look at it from arm's length, not through a loupe — engraving is judged at viewing distance. Raising lines per cm past the point where the lines stop being visible just buys machine time nobody can see.
Five mistakes that make a test lie to you
Re-using focus from the last job
Focus is set for one exact material thickness. A grid run out of focus tests a wide, weak beam and every square looks bad. Re-focus for the sheet in front of you before the grid, not after.
Testing on a different sheet than the job
Run the grid on an offcut of the same sheet. A different batch of the same nominal material is a different material as far as the laser is concerned.
Steps that are too big
Jumping 100% to 60% power in one step tells you almost nothing. Five steps across a range you already believe is close beats three steps across a range you are guessing at.
Turning air assist off to 'see better'
Air assist changes the result more than most setting tweaks on wood - it clears smoke out of the kerf. Test with the air assist you will actually use on the job, at the same pressure.
Judging a cut from the top face
The top always looks fine. Flip the piece: the back face tells you whether the beam made it through cleanly or barely scraped out.
Write the result down
The grid is worthless if the number lives in your head until next month. Keep a material library — LightBurn has one built in — with material, thickness, supplier, focus, air assist and the winning power/speed/passes. Supplier belongs in there: it is the field that explains why last month's settings stopped working.
Once you have a reliable speed for a material, it stops being a settings question and becomes a pricing one. Our cutting time calculator turns a path length and that speed into machine time, and the file calculator does it straight from your SVG, DXF or PDF. Typical speeds per material are listed on our material pages.
Starting points to bracket
Do not start a grid from nothing — start it around a number that is already close:
- Power & speed chart by wattage — 5 W to 100 W, diode and CO2.
- Settings for plywood and MDF
- Settings for acrylic
- Settings and speeds for your exact machine — xTool, Glowforge, OMTech, Creality Falcon, Trotec, Aeon and more.
If the grid still will not cut through at any setting, the problem is usually not the settings: see why won't my laser cut all the way through? If there is no beam at all, see laser powers on but won't fire. For a material nobody has published settings for, see settings for a material with no chart. For scorched edges on an otherwise good cut, see how to stop burn marks on wood.
FAQ
How long does a laser material test grid take?
About 10-15 minutes for a cut grid and 5-10 for an engrave grid, including setup. A 5x5 grid of 15 mm squares is enough for most work. That is far less time than the material you waste guessing settings on a real job, and you only do it once per material and thickness.
What power and speed range should I test?
Bracket the chart value rather than starting from zero. Take a known starting point for your machine class, then test roughly half to double that speed and a power band around it. On a 40 W diode cutting 3 mm plywood that means about 300-900 mm/min at 80-100% power; on a 60 W CO2 it means about 8-20 mm/s at 55-95%. If every square cuts, your range was too slow — retest faster.
How do I read a cut test grid?
Push the squares out from the back. The best setting is the fastest, lowest-power square that releases cleanly with a light push and no charring on the back face. Do not pick the square with the darkest edge - that is overburn. If nothing releases, drop the speed or add a pass rather than raising power to 100% and holding it there.
Why do my settings stop working on a new sheet?
Material batch is the biggest hidden variable. Plywood glue lines, moisture content and even the colour of the top veneer change how much power reaches the bottom of the kerf, and acrylic cast vs extruded behaves differently. A lens that needs cleaning or a diode past its first few hundred hours shifts the numbers too. Re-run a small grid when you open a new batch.
Should I test at 100% power?
Include 100% in a cut grid so you can see the ceiling, but do not choose it as your working setting. Running a CO2 tube or a diode flat out continuously shortens its life. If only the 100% square cuts through, slow the speed or add a second pass instead - that gets you the same result at 80-90% power.