What Can a K40 Laser Cut? Materials, Thickness and Starting Settings

What a K40 cuts well, with typical single-pass thickness for a healthy tube and air assist:

• Plywood and softwood: about 3mm easily, up to around 6mm with slow speed or two passes.
• MDF: about 3mm. The resin makes heavy smoke and a dark edge.
• Cast and extruded acrylic: about 3–6mm, with a glossy, flame-polished edge.
• Veg-tan leather: thin hides cut cleanly; thick belt leather takes passes.
• Paper, card and cardboard: fast, at low power.
• Felt, cotton, cork and laser-safe rubber: clean cuts for gaskets, stamps and patterns.

Hardwoods cut slower than softwoods, and plywood varies with its glue. A sheet that cuts perfectly one week can stall the next if the new batch has thicker glue layers.

Colour does not matter to a CO2 beam, which is one of its big wins over a diode. Clear, blue and white acrylic all cut the same, as the K40 vs diode comparison explains. For K40 laser acrylic work, buy cast sheet when the part needs an engraved mark and extruded when it only needs cutting.

Five things decide your real limit:

1. Tube power. A stock 40W tube run at a safe current delivers less than the badge suggests. A 45W tube, like the one in the OMTech K40+, goes deeper.
2. Air assist. Air blows out the burning debris and stops flare-ups, so each pass cuts deeper and cleaner.
3. Focus. A spot out of focus spreads the power. Set it with a ramp test.
4. Clean, aligned optics. A dirty lens or a drifted mirror can cost a large share of the power.
5. Density and moisture. Dense hardwood and damp stock both cut slower.

More passes go deeper, but each one widens the kerf and darkens the edge. For thick stock, lower the focus a little between passes so the spot follows the cut.

The makers' own figures show how far claims can differ. OMTech rates the K40+ 45W for 10mm acrylic and 8mm wood. VEVOR recommends staying at or under 5mm acrylic and 3mm wood on its 45W machine.

Treat any top figure as a best case with slow speed and several passes. For projects, design around 3mm stock and you will rarely be disappointed.

For K40 laser engraving, glass gives a frosted mark, because the beam heats the surface and it micro-fractures. It does not cut glass at all. To keep the frosting smooth:

• Lay a damp paper towel or a thin film of dish soap on the glass.
• Use low power and moderate speed; more power means more chipping.
• Engrave twice lightly rather than once hard.
• Wipe off the dust with a soft brush, not your fingers.

Round glasses and bottles need a rotary. Stock K40 boards have no dedicated rotary port, so owners rewire the Y axis; the K40+ offers a rotary bundle, and the VEVOR 45W includes one.

Other good engraving materials:

• Slate: engraves a clean light grey on the dark stone.
• Ceramic tile and stone: engrave, often filled with paint afterwards.
• Anodized aluminium: the beam strips the dye and leaves a bright white-silver mark.
• Painted and powder-coated metal: the beam removes the coating down to the metal.
• Cast acrylic: engraves frosty white; extruded acrylic gives weak contrast.

All engraving work still needs the exhaust running. Glass and stone throw fine dust, and coatings burn off as fumes.

What it can do is mark metal, with help. A CO2 marking spray bonds to bare metal under the beam and leaves a permanent black design. The OMTech marking spray is made for CO2 lasers of 25W and up, which covers every K40.

1. Clean and degrease the metal so the coat sticks.
2. Spray a thin, even coat. It goes on white and turns black only where the laser hits.
3. Let it dry. Under five minutes, or about two with a hot-air blower.
4. Engrave at a moderate speed and power, then test on scrap first.
5. Rinse the excess off with water. The laser-marked design stays.

The spray works on stainless steel, aluminium, brass and most other metals. It suits tool serial numbers, tags, tumblers and jewellery blanks.

If bare-metal marking is your main job, a fiber laser is the proper tool. For occasional tags and tumblers, spray on a K40 does the work.

Stock K40s set power with a knob and show it on an ammeter in milliamps. Digital machines set power as a percentage, so start low and read the ammeter if one is fitted.

Build your own chart in three steps:

1. Cut a grid of small squares, each at a different speed and power.
2. Note the fastest square that dropped out cleanly.
3. Write it on a card taped inside the lid, with the material and thickness.

Keep the current at or under about 15mA on a 40W tube, whatever the material. Running harder buys a little depth and costs a lot of tube life.

If settings that used to work stop working, the machine changed, not the wood. Check the optics and mirror alignment first, and keep the K40 fume and fire precautions in place for every material.