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Laser engraving tips: safe materials, tests and focus

Laser engraving tips that hold for any hobby machine: materials never to laser, fumes, eyes and fire, then a test grid, focus, line interval and masking.

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The tips that matter most for laser engraving are the same on a small diode machine and a large CO2 one. Know what your material is before it goes in. Send the fumes outside. Protect your eyes. Never leave the machine running alone. Then, for every new material, burn a small grid of test squares before the real piece. The settings other people publish are starting points for that grid and nothing more: the right power and speed depend on your laser, its focus and the piece of material in front of you.

Each point below comes from a laser maker’s or a safety body’s own pages, named where it is used and listed at the end.

Materials that must not be lasered

None of the makers’ pages read for this guide has a list that covers everything, so the rule is Glowforge’s: “If you aren’t completely sure that your material is laser-compatible, do not put it in the Glowforge.” It is a sound rule for any laser. Glowforge tells you to contact the manufacturer, inspect the safety data sheet or consult an expert, and Epilog also points to the data sheet, which lists what a material is made of. These are the materials those pages name:

MaterialWhat the maker saysSource
PVC and vinyl“Hydrogen Chloride and Vinyl Chloride (mostly found in PVC and other man made materials) are hazardous to the life of your laser system.” Vinyl “can release hazardous gases that can hurt you and damage your Glowforge”Epilog, Glowforge
Kydex“Materials, such as Kydex, contain PVC”Epilog
Chrome-tanned leatherTanned with chromium, “which could be released during the Glowforge printing process and create hazardous smoke and fumes”. Glowforge contrasts it with vegetable-tanned leather, which is tanned with plant tanninsGlowforge
Galvanised metalWhen cut or engraved, “they can release hazardous gases and damage your Glowforge”Glowforge
Copper, chrome and other metals that reflect the laserSaid of Glowforge’s own CO2 machines: “materials that reflect laser light are not laser-compatible. Copper and chrome can reflect the infrared laser light, which can be hazardous to people and damage your Glowforge”Glowforge
Some plywood“some plywood contains glue that isn’t laser-compatible”. Trotec advises white-glued plywood or boards made for lasersGlowforge, Trotec
ABS and HDPENamed with vinyl and PVC among the plastics that “can melt or release toxic or corrosive fumes that could harm you or your Glowforge”Glowforge
Coated, dyed, painted or glued materials of unknown make“certain plywood glues, inks, adhesives, dyes, and paints may not be laser-compatible”Glowforge

The trouble with PVC is that it looks like other plastics. Glowforge warns that “many plastics look alike”, and that vinyl “can be mistaken for some laser-compatible materials”. If you cannot find out what a plastic is, leave it out. Even masking tape counts: Trotec’s wood guide says to use tape that is PVC-free.

Your own machine’s manual has its maker’s list, and it takes priority over this table.

Fumes

Every material gives off smoke, including the safe ones. Glowforge’s safety page says the smoke and fumes “can include carbon monoxide and other chemicals which present health hazards”, and that its machines must only run when “exhausted to the outdoors” or through the maker’s filter. Trotec says of wood that “the use of a suitable exhaust system is essential”, and Epilog says the fine particles and fumes from engraving glass “must be safely removed from the workspace”.

For an open-frame machine, xTool’s safety article advises an enclosure that surrounds the whole laser, and “a proper ventilation system that purifies the smoke before it’s released into the atmosphere”. An open window alone is not what any of these makers describe. Glowforge also says not to open the lid until the fans stop.

Eyes

The UK Health Security Agency’s guidance on laser safety puts any laser above 500 mW in Class 4, “for which intrabeam viewing and skin exposure is hazardous and for which the viewing of diffuse reflections may be hazardous. These lasers also often represent a fire hazard.” Engraving lasers are rated in watts, so nearly all of them are above that line; xTool’s safety article says laser machines “predominantly fall under Class 4”. The same guidance says that under the British standard for consumer laser products, “Class 3B and Class 4 lasers are not suitable for general use by consumers”, which is why the enclosure matters so much.

A machine sold as a Class 1 product is not a weak laser. As xTool explains, a Class 1 laser product can hold a Class 4 laser: it is the enclosure that keeps the light in, often with a shut-off that stops the laser if the enclosure is opened. Glowforge describes its closed machines the same way, as Class 1 products that “contain an embedded Class 4 laser”, and classes its Pro model as Class 4 because of its pass-through slots.

So:

  • With an enclosed machine, keep the lid shut and never defeat the lid switch.
  • With an open-frame machine, wear laser goggles “that cover the wavelength range of your laser machine”, in xTool’s words. UKHSA’s description of Class 4 says even “the viewing of diffuse reflections may be hazardous”, so the risk is not only to the person at the controls.
  • LightBurn’s safety page says simply: “Always wear proper eye protection when using your laser.”

Fire

LightBurn’s documentation shows one of its own staff’s lasers after it burned, and says it took only a few minutes to go from “the first hints of sustained flame” to a destroyed machine; the spread it shows on film took about four. Its list of preparations:

  • “Never run your laser unsupervised. A camera feed does not count as supervision.”
  • Keep a smoke detector near the laser.
  • Keep a fire extinguisher, a fire blanket and a spray bottle of water within reach, and know how to use them.
  • Know how to stop the laser quickly.
  • Keep the inside clean. Offcuts in the tray under the bed “can act like kindling”.
  • Take extra care with materials that have air pockets, “like corrugated cardboard or some plywood”.

Glowforge adds that a small flame that follows the beam is normal, and a flame that stays lit after the beam has moved on is not. Epilog singles out acrylic as “especially flammable when cut with the laser”. If something does catch, LightBurn’s first step is to stop the laser and turn off the air assist.

Burn a test grid for every material

A test grid is a block of small squares, each engraved at a different power and speed. You pick the square that looks right and use its settings. It costs a few minutes and a scrap, and it is the only way to get settings you can trust.

In LightBurn (version 2.1 documentation), the tool is under Laser Tools, then Material Test. By default it makes a grid of 10 by 10 squares that vary power and speed, and it can vary line interval or the number of passes too. Two details from the documentation are worth knowing:

  • The squares run in order of risk, with the fastest and weakest first, which lets you stop the test if the material starts to char.
  • Check the units. “A given number of millimeters per second is much faster than that same number in millimeters per minute”, and a speed entered in the wrong unit can mean a weak mark or, at the slow end, a fire.

Other programs have their own version. Trotec’s is a “grayscale matrix” of 100 squares, each engraved at a different share of the set power. If your software has none, draw a row of squares and give each its own setting.

Use the same scrap as the real job: the same board, not just the same species. Write the chosen settings on the scrap and keep it.

Focus

A laser engraves finest when the material sits at the focus of the lens. LightBurn’s documentation notes that diode machines usually come with a focusing spacer, and that CO2 machines are focused with a spacer or by autofocus. Your maker’s instructions say which. Focus on the surface you will engrave, and focus again when the thickness changes.

LightBurn’s Focus Test (Laser Tools, then Focus Test) engraves a row of lines at stepped heights so you can pick the sharpest, but it needs a machine with a motorised Z axis. Its documentation advises setting the power “just high enough to mark your material”, because a line that chars is hard to judge.

Out of focus is sometimes used on purpose. Trotec notes that defocusing by about 0.5 to 2 mm makes a darker engraving on wood, because the wider spot burns more of the wood and vaporises less of it, and that “details can be lost”.

Line interval

The rows of an engraving should just meet. LightBurn’s documentation: “The ideal Line Interval will produce lines that just touch, without overlapping.” Too close and the engraving goes dark and takes longer; too wide and it shows stripes. LightBurn’s Interval Test (Laser Tools, then Interval Test) engraves squares at stepped intervals, and suggests trying 0.08 to 0.16 mm as a first range. The laser engraving DPI guide explains how interval, DPI and spot size relate.

Keep smoke off the surface

Brown haze round an engraving is smoke that has settled on the surface. Three things reduce it:

  • Masking. Cover the surface with masking tape or application tape and engrave through it, then peel it off. xTool advises laying it flat with no bubbles or overlaps. Trotec adds that tape suits large shapes and cutting but not photos or very fine work, “since many small parts have to be removed later”.
  • Air assist. A stream of air at the beam pushes smoke away. Trotec recommends it for cutting wood in particular.
  • A raised bed. xTool points out that marks on the back come from smoke trapped under the sheet, and that a honeycomb panel lets it escape.

Prepare the artwork for the machine

Glowforge’s tips for engraving are short and apply to any laser: start from a vector where you can; for a photo, use a source of at least 300 DPI, raise the contrast until “the lightest areas are pure white and the darkest areas are pure black”, and sharpen it.

A photo then has to become dots or lines, because most materials only mark or do not. Plotcaster turns a photo into a dithered, stippled or line drawing in your browser, and dithering for laser engraving explains which to choose.

By material

Questions

Are the settings in a maker’s material library right as they are? Use them as the middle of your test grid. Your board, your focus and your machine are not the ones they were found on.

Do I need goggles with an enclosed laser? Follow the machine’s manual. The enclosure and its filtering lid are what make such a machine Class 1. Glowforge’s safety page says not to use its machine “if glass or case are damaged or modified”, and not to defeat the lid switches.

Can I engrave a material that is not on any list? Only once you know what it is made of. Ask the supplier for the safety data sheet. If it contains PVC or vinyl, the answer is no.

Sources