Why does the same setting cut one sheet of plywood but not the next?

Plywood varies. Glue layers, density, moisture and warping change how much energy it takes to get through. A single sheet can even cut differently in the middle and at the edge, so test on an offcut from the same sheet.

Is it better to cut slower with fewer passes or faster with more passes?

On diode lasers, several faster passes often give a cleaner cut with less charring because the beam stays focused on fresh material and air assist clears smoke between passes. On CO2, one pass at the right speed is usually best.

What does 100% power mean on a diode in LightBurn?

It means the maximum of the module, for example 10 W optical output on a 10 W module. Diodes are normally cut at 100% because lower power with slower speed mostly adds heat and burn marks.

Does LightBurn use mm/s or mm/min?

LightBurn can show speed in either, depending on a preference setting. Many GRBL diode profiles use mm/min, while CO2 profiles use mm/s. Always check the unit before copying numbers from a tutorial: 300 mm/min is only 5 mm/s.

How do I find the right settings fast?

Use the Material Test generator in LightBurn to cut a small grid of speed and power combinations on scrap, then pick the fastest square that cuts all the way through cleanly.

LightBurn Settings for 3 mm Plywood (Diode and CO2)

You press Start, the laser hums along your outline, and you lift the piece out with a little drum roll in your head. It is still stuck at the corners. We have all been there. The good news is that 3 mm plywood is the friendliest material in laser cutting, and a few sensible starting numbers get you most of the way.

This guide gives you realistic LightBurn settings for 3 mm plywood on diode lasers (5–20 W optical) and CO2 lasers (40–100 W), plus the way to fine-tune them in ten minutes with a test grid. Treat every number as a starting range. Always test on scrap from the same sheet you are about to cut.

Starting settings for cutting 3 mm plywood

Plywood is a sandwich of thin wood layers and glue. Different sheets (birch, poplar, basswood, Baltic birch) behave differently, and cheap sheets with hard glue lines are the usual troublemakers. The table shows typical starting ranges for a clean cut-through with air assist on.

Laser	Speed (LightBurn, mm/s)	Power	Passes	Notes
Diode 5 W optical	1.5–3	100%	4–8	Marginal for plywood; thin basswood ply works best
Diode 10 W optical	3–6	100%	2–4	The common hobby choice
Diode 20 W optical	6–15	100%	1–2	Often one pass on good birch ply
CO2 40 W	8–15	60–85%	1	Watch for the second pass only on stubborn glue lines
CO2 60 W	12–25	50–75%	1
CO2 80–100 W	20–40	45–70%	1	Fast, so check corners for burning

Speeds above are in mm/s. If your profile shows mm/min, multiply by 60 (4 mm/s equals 240 mm/min). To give you a sense of real jobs: our reindeer ornament has a cut length of 0.47 m, and the estimated time is about 1 min 48 s on a 10 W diode, 44 s on a 40 W CO2 and 22 s on a 100 W CO2. Those are estimates for planning, not magic settings, but they show the scale.

Pro tip: On a diode, set a lower speed and 100% power rather than 70% power and slower speed. The beam cuts instead of smouldering, and your edges stay lighter.

Set up your layers in LightBurn

A neat file makes setup painless. Our files use two colours: a red hairline for the cut and black fills for engraving. When you import an SVG or DXF, LightBurn maps each colour to a layer, so you adjust each layer once.

Import your file with File, Import (or drag it into the workspace).
Check the size in the Shape Properties panel before anything else. If it is wrong, see how to scale laser files.
Click the cut layer (red) in the Cuts / Layers panel and set mode to Line, with your speed, power and passes.
Click the engrave layer (black) and set mode to Fill, with a line interval of about 0.1 mm for most wood.
Make sure the engrave layer is listed first, so the piece is still held in place while engraving, and the cut layer runs last.
Turn on air assist for the cut layer.

Layer	Mode	Typical interval	Order
Engrave (black)	Fill	0.08–0.15 mm	First
Score (optional)	Line, low power	n/a	Second
Cut (red)	Line	n/a	Last

Engrave settings that go with the cut

Most ornaments are engraved and cut in one job. For wood, a diode usually engraves at much lower power than it cuts, and a CO2 engraves very fast at low power. The numbers below are typical starting points on 3 mm plywood, a gentle brown engraving. For dark, deep engraving see speed and power for engraving wood.

Laser	Engrave speed (mm/s)	Power	Line interval
Diode 5 W optical	40–100	40–80%	0.1 mm
Diode 10 W optical	60–150	20–50%	0.1 mm
Diode 20 W optical	100–250	15–40%	0.1 mm
CO2 40 W	150–300	10–25%	0.1 mm
CO2 100 W	300–500	8–20%	0.1 mm

Run a material test instead of guessing

This is the habit that saves the most plywood. LightBurn has a Material Test generator under the Laser Tools menu. It cuts a grid of small squares where speed changes in one direction and power in the other, and you pick the best one.

Open Laser Tools, then Material Test.
Set the speed range around the table above (for a 10 W diode, 2 to 8 mm/s) and the power range, for example 60% to 100%.
Keep the squares small (about 10 mm) so you do not waste the sheet.
Run it on an offcut from your actual sheet, with the same focus and air assist.
Lift out the squares. The fastest one that dropped out cleanly is your cutting speed. Add a small safety margin, about 10%, so a slightly thicker part of the sheet still goes through.

Common mistake: Copying settings from a video and skipping the test. Their plywood, their focus and their laser's real output are not yours. Ten minutes of testing beats a ruined sheet.

When the cut does not go all the way through

Run through this list in order, from cheapest fix to biggest.

Problem	Likely cause	Fix
Cuts through in the middle but not at corners	Machine slows in corners, or focus drifts	Lower speed 10–20% or add one pass
Bottom of the cut is stuck in places	Hard glue line or warped board	Weigh the sheet flat, add a pass
Heavy char on the bottom face	Too slow, too many passes, no air	Raise speed, use air assist, put a honeycomb or slats under the sheet
Cuts well one day, not the next	Dirty lens, different sheet, humidity	Clean the lens, retest

Focus matters as much as power. A spot that is out of focus by a millimetre can halve your cutting performance, especially on a diode. See how to focus a laser and why a laser is not cutting through.

Pro tip: Tape the sheet flat with painter's tape or use magnets. A bowed plywood sheet changes the focus distance from one edge to the other, and that is where most mysterious half-cuts come from.

Reduce burn marks and keep the edges light

Brown edges are the price of fire, but you can control them. Use air assist, cut at the fastest speed that still goes through, and cover the top with masking tape if your plywood has a finish you care about. For more on this, see how to prevent burn marks on wood. Wipe the edges with a damp cloth or a quick sand with a fine sponge and you will get a cleaner look.

Diode versus CO2: what feels different

On a diode you are trading time for control. Expect a slower, gentler cut, a bit more smoke, and a dark edge that needs a quick wipe. The reward is a small, quiet machine that fits on a desk. On a CO2 the cut is fast and the edge is paler, but the lens, mirrors and tube need care, and alignment can drift after a bump. In both cases the habit that matters most is the same: change one setting at a time and write it down.

Thing to watch	Diode	CO2
Biggest risk	Charring from slow multi-pass cuts	Burning at corners from too much power
First thing to check when a cut fails	Focus distance	Lens cleanliness and alignment
Air assist	Almost always needed	Strongly recommended
Typical bed	Small	Often larger

Cutting several sheets in a row

Settings drift as the day goes on. The lens gets a smoke film, the sheet batch changes, and the room warms up. After every 20–30 minutes of cutting, wipe the lens, check that the first piece of a new sheet drops out cleanly, and keep one known-good test square as a reference. If cut quality changes suddenly, the cause is nearly always a change in material or a dirty lens, not the software.

Next step

Pick one ornament, for example the six-pointed snow star, and run a material test on an offcut first. Write the winning numbers on a sticky note and keep it on the machine, with the sheet brand and date. In a month you will have a small settings library that is worth more than any table in this article.