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Laser engraving on wood: which wood, settings and finish

How to laser engrave wood: which woods engrave evenly, how to find power and speed with a test grid, and how to stop smoke stains before staining or sealing.

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Wood is one of the most popular materials to laser engrave, and one of the least predictable. The beam burns the surface and leaves a brown mark, and how dark and how even that mark is depends on the board: its species, its density, its resin and its grain. Pick wood with an even colour and grain, find the power and speed with a test grid on an offcut of the same board, and keep the smoke off the surface. Both diode and CO2 lasers engrave wood.

Which wood to engrave

Trotec’s rule of thumb is the best one-line guide: “The more uniform the coloring and grain of the wood, the better and more even the laser engraving.”

WoodHow it engravesSource
Soft, light woods such as balsa and poplarNeed less power and engrave faster. The mark is lighter, with less contrastTrotec
Dense hardwoods such as oak and cherryNeed more power. The mark has more contrastTrotec
Conifers such as larch and fir“not suitable for laser engraving”: hard grain lines in soft wood, so no one setting suits bothTrotec
PlywoodEngraves well. The glue matters, mostly when cutting: choose white-glued boards or ones sold for lasersTrotec, Glowforge
MDFEven all through, so it “can be easily engraved and cut”. Cut edges turn very darkTrotec

Epilog shows engraved samples of maple, birch plywood, alder, bamboo plywood, MDF and walnut on its wood page, and says its laser systems “work well with nearly all types” of wood. Its own answer to which woods are best is alder, cherry and maple, which it describes as fine-grained and low in resin; it says high-resin woods such as pine, cedar and spruce “tend to burn inconsistently and produce excessive smoke”.

Three more properties decide the look:

  • Resin. xTool’s guide says woods with little resin give “lighter, crisper engravings” and resinous woods give darker ones. Trotec adds that dry wood without resin gives lighter cut edges.
  • Colour. A pale board shows a brown burn better than a dark one, so xTool recommends lighter woods for engraving.
  • Grain. A strong grain pattern can show through the engraving and make it harder to read.

Plywood needs a check before it goes in. Glowforge warns that “some plywood contains glue that isn’t laser-compatible”, and Trotec says the type of glue matters most when cutting. Ask the supplier, or buy board sold for laser work. Painted, varnished, treated or reclaimed wood has the same problem: you do not know what is on it, and it should stay out of the laser until you do.

Finding power and speed

No table of settings from another machine will be right for yours, and the same species varies from board to board. The method is always a test grid:

  1. Take an offcut of the same board as the real piece.
  2. Focus on its surface.
  3. Engrave a grid of small squares, with power rising along one side and speed along the other. In LightBurn this is Laser Tools, then Material Test, which makes a 10 by 10 grid by default (version 2.1 documentation).
  4. Choose the square with the colour you want and no char round its edge, and use those settings.

Where to start the grid depends on the machine, so begin from the wood settings that came with it. Trotec’s starting points for its own test matrix on its CO2 machines are given as percentages, which shows how little a number means away from its machine: full power at full speed for a 40 to 100 W laser, and full power at half to 80% speed below 40 W, at 333 to 500 DPI on wood.

Focus changes the colour as well. Trotec’s tip: defocusing by about 0.5 to 2 mm gives a darker engraving, because the wider spot burns more of the wood. “The disadvantage is that details can be lost.”

Photos on wood

Most photos on wood are engraved as a pattern of dots: dark areas get many, light areas few. That conversion is called dithering. Glowforge’s software calls it “Convert to dots”, which it finds “works best for engraving curvaceous and organic images, such as photographs”, and LightBurn’s documentation lists ten image modes, most of which shade with patterns of dots.

Wood spreads each dot, so the common fault is a photo that comes out too dark. Three guides on this site cover the fixes:

Plotcaster does the conversion in your browser and saves a black and white PNG at your laser’s DPI. For outlines without shading, the photo to wood burning pattern guide makes single-line drawings that a laser can score.

Keeping the surface clean

The brown halo round an engraving is smoke that has settled on the wood. xTool’s guide puts it down to the dark particles in the fumes sticking to the surface. It is easier to prevent than to remove.

  • Mask it. Lay masking or application tape over the surface, engrave through it, and peel it off. xTool says to press it down with no bubbles and no overlaps, which would engrave unevenly. Trotec says to check the tape is PVC-free, and that tape suits larger areas and cutting but not photos or very fine work, “since many small parts have to be removed later”.
  • Use air assist. A jet of air at the beam blows smoke away. Trotec recommends it above all for cutting.
  • Lift the board. xTool puts marks on the back down to smoke trapped underneath, and recommends a honeycomb panel to let it out.
  • Extract. Trotec calls a suitable exhaust system essential for wood, because of the dust and gases.

Trotec notes that wood dust is “extremely sticky due to the resins and oils it contains” and settles inside the machine, so the machine needs regular cleaning too.

Staining and sealing

There is a choice of order, and each has a cost.

Stain first, then engrave. xTool’s guide recommends this, so that the engraving contrasts sharply with the stained background. The stain must be completely dry, because, as xTool warns, it can be flammable. You also need to know what the stain is made of before lasering it: Glowforge’s safety page warns that stains and finishes on hardwood “can release toxic or corrosive fumes”.

Engrave first, then finish. xTool’s reason for staining first is contrast. If you would rather stain afterwards, try the stain on your engraved test grid before the real piece.

For sealing, xTool suggests a clear coat such as polyurethane, lacquer or varnish. If the board is rough or uneven, xTool advises sanding it before engraving.

Deep and 3D engraving

Wood can be engraved to different depths in one piece, so the picture stands up in relief. Trotec calls wood “a great material for relief engraving” and advises several passes at high power followed by one or two light, fast passes to clear the smoke residue. It cleans the finished relief with a toothbrush, soap and a little water, and dries it well so that the wood does not warp. The file for this is a greyscale picture in which each shade means a depth. 3D laser engraving explains how those files work.

Questions

Can a diode laser engrave wood? Yes. Diode and CO2 lasers both engrave wood. xTool’s guide notes that the blue light of a diode suits “materials like wood and leather”.

Why is my engraving patchy? Often the wood. Trotec notes, of relief engraving, that the growth rings of oak differ in density, which gives an uneven result, and its rule of thumb is that even colour and grain engrave most evenly. Choose a more even board, or one with finer grain.

Why are the edges of the engraving brown? Smoke. Mask the surface, add air assist and check the extraction.

Is MDF safe to laser? Trotec lists MDF as easy to engrave and cut, and sells MDF panels that it has tested for laser work. Glowforge’s advice for any board it has not tested is to check with the manufacturer that it is compatible with your laser. Extract the fumes as for any wood.

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