How Thick Can Your Laser Actually Cut? Wattage-to-Thickness Ceilings for Diode and CO2
Every machine has two thickness ceilings: what it will cut in one pass at a slow speed, and what it will get through with multiple passes and an edge you may not want to sell. A 10W optical diode manages 3 mm plywood single-pass and about 6 mm with patience; a 60W CO2 does 9 mm single-pass and 15 mm at the limit. Size to about 60-70% of the practical maximum if the work is production, not one-offs.
Wattage-to-thickness charts fail for one reason: they use the advertised watt figure, and that figure is measured at the wrong end of the machine. A marketplace "80W diode" that draws 80W from the wall is putting maybe 10 optical watts on the workpiece. A CO2 tube sold as 80W frequently measures nearer 70W new, and the beam then loses another 6-12% crossing three mirrors and a lens.
So each row below carries its own optical figure alongside the advertised one, and the thickness columns are keyed to the optical figure. Two ceilings are given for every material. The single-pass number is what the machine severs in one slow pass with the right lens and working air assist. The practical maximum is what it will get through eventually, with an edge quality you might not want a customer to see.
Two ceilings, and only one of them is a buying number
Buy to the single-pass column. That's the honest answer, and it's the one nobody wants to hear because it means spending more.
The reasoning is dull but sound. Multi-pass cutting doesn't just multiply time — it compounds heat into the kerf walls, widens the kerf at the top, and leaves a taper as the beam converges below the focal point. On plywood you also get glue-line ridges that snag and char. A machine running at 60-70% of its practical maximum cuts clean, fast and repeatably. A machine running at its ceiling produces one good part in three and a smell that lingers.
If you're cutting 6 mm ply for a living, the machine you want is the one with a 9 mm single-pass rating, not the one with a 6 mm one.
Rigid sheet: plywood, MDF and cast acrylic
Machine as advertised Optical W at the workpiece Birch ply — single pass / practical max MDF — single pass / practical max Cast acrylic — single pass / practical max Typical speed cutting 3 mm ply 5W diode 4.2-5.2 W 1.5 mm / 3 mm 1 mm / 3 mm Clear: none. Black: 0 / 3 mm 150-250 mm/min, 3-4 passes 10W diode 9-10.5 W 3 mm / 6 mm 2.5 mm / 6 mm Clear: none. Black: 2 mm / 5 mm 180-300 mm/min, 1-2 passes 20W diode 17-21 W 5 mm / 10 mm 4 mm / 9 mm Clear: none. Black: 4 mm / 8 mm 300-600 mm/min, 1 pass 40W diode 32-40 W 6 mm / 12 mm 5 mm / 10 mm Clear: none. Black: 6 mm / 10 mm 600-1200 mm/min, 1 pass 40W CO2 (K40 class) 25-31 W 4 mm / 8 mm 4 mm / 7 mm 5 mm / 8 mm 360-600 mm/min 40W CO2 (branded tube) 34-38 W 6 mm / 10 mm 5 mm / 9 mm 6 mm / 10 mm 480-720 mm/min 60W CO2 48-56 W 9 mm / 15 mm 8 mm / 12 mm 10 mm / 15 mm 720-1080 mm/min 80W CO2 58-70 W 12 mm / 18 mm 10 mm / 15 mm 12 mm / 20 mm 900-1500 mm/min 100W CO2 80-94 W 15 mm / 20 mm 12 mm / 18 mm 15 mm / 25 mm 1200-1800 mm/min 130W CO2 105-120 W 18 mm / 25 mm 15 mm / 20 mm 20 mm / 30 mm 1500-2400 mm/min Find the row matching the optical figure your machine actually delivers, then buy stock at or below the single-pass column. Acrylic figures are cast sheet with a 2-inch lens up to 6 mm and a longer lens above that. Extruded acrylic behaves differently from cast and cuts marginally faster, but it engraves to a poor, barely-visible frost and stress-crazes at the kerf. For anything with an engraved element, use cast.
The clear-acrylic entries in the diode columns say "none" and they mean it. A 445nm beam passes through clear acrylic almost unimpeded. No wattage fixes that — it's a wavelength problem, and it's the sharpest single dividing line between diode and CO2.
Soft goods: leather, foam, fabric and card
Different physics, different limits. These materials absorb readily and cut fast, so the constraint stops being raw power and becomes edge quality, scorching and how well your extraction copes.
Machine as advertised Optical W at the workpiece Veg-tan leather max EVA foam max Cotton / poly fabric Typical speed cutting 2 mm leather 5W diode 4.2-5.2 W 2 mm 3 mm, black stock only 1 dark layer 250-350 mm/min, 2 passes 10W diode 9-10.5 W 3 mm 5 mm, black stock only 1-2 dark layers 400-600 mm/min 20W diode 17-21 W 4-5 mm 8 mm, black stock only 2-3 dark layers 900-1500 mm/min 40W diode 32-40 W 6 mm 10 mm, black stock only 3-4 dark layers 1500-2400 mm/min 40W CO2 (K40 class) 25-31 W 4 mm 8 mm, any colour 2 mm stacked, any colour 1500-2400 mm/min 40W CO2 (branded tube) 34-38 W 5 mm 10 mm, any colour 3 mm stacked 1800-3000 mm/min 60W CO2 48-56 W 6 mm 15 mm, any colour 4 mm stacked 2400-3600 mm/min 80W CO2 58-70 W 8 mm 20 mm, any colour 5 mm stacked 3000-4200 mm/min 100W CO2 80-94 W 10 mm 25 mm, any colour 6 mm stacked 3600-4800 mm/min 130W CO2 105-120 W 12 mm 30 mm, any colour 8 mm stacked 4200-6000 mm/min Use this table to decide whether a diode covers your product line. If the answer involves light-coloured EVA or white fabric, it doesn't — colour, not thickness, is the wall. Colour dominates on the diode rows. Blue light reflects off white and pale materials, so a 20W diode that slices 8 mm black EVA will barely scuff the same foam in white. CO2 at 10.6 µm doesn't care what colour the material is, which is why every commercial foam-insert shop runs CO2.
One caution on fabric: polyester seals its own edge under the beam, which is genuinely useful, and cotton doesn't, which means fraying. Neither is a machine fault.
What each extra pass actually costs
Passes are not free and they're not linear. Every pass adds a return move, an acceleration ramp and another dose of heat into walls that are already hot.
Passes Time vs single pass Kerf taper, top to bottom Edge on 6 mm birch ply Verdict 1 1.0x 0.02-0.05 mm Light amber, wipes clean Ideal. This is what you sized the machine for. 2 2.1x 0.05-0.10 mm Amber to mid brown Fine for production work. 3 3.2x 0.10-0.15 mm Brown with light soot Acceptable, sand-free assembly still works. 4 4.3x 0.15-0.25 mm Dark brown, soot on the underside The sensible limit. 6 6.5x 0.25-0.40 mm Black, glue-line ridges visible You're fighting the machine now. 8 8.8x 0.40 mm and up Charred, kerf bells out at the top Change lens, change material, or change machine. If your everyday job needs more than four passes, the fix is a longer focal length lens or a thinner stock, not more passes. Read this table before you convince yourself the machine is fine. The jobs a diode simply cannot take
- Clear or lightly tinted cast acrylic, at any wattage. The beam goes straight through.
- Clear glass. Same reason. A coating gets you a mark, not a cut.
- White, cream or pale EVA, foamboard and fabric. Reflection, not power, is the limiter.
- Bare or polished metal. Diodes mark anodised dye and powder coat because they're attacking a coating; they don't cut steel.
- Anything where a flame-polished acrylic edge is the selling point. That edge comes from CO2's melt-and-vaporise behaviour at 10.6 µm.
Sizing a machine to work you already have
Work backwards from the thickest material you'll cut regularly, not the thickest you might cut once.
Write down that thickness. Find the row where it appears in the single-pass column. That's your floor. Then add one row if you want the job done at a speed that's worth quoting for, because cutting at the single-pass limit means crawling, and crawling means the part costs you an hour.
Bed size deserves the same treatment. A 400 x 400 mm bed sounds generous until you try to nest an A2 sheet and discover you're cutting everything twice with a registration jig.
Air assist buys more depth than the next power step
A decent air assist on a 40W CO2 will out-cut a poor one on a 60W. That's not a rhetorical flourish — the plume of hot smoke sitting in the kerf absorbs and scatters the beam before it reaches the bottom, and clearing it restores power you already paid for.
For cutting, you want a focused stream through a small nozzle, not a gentle breeze. A small oil-free compressor or a 30 litre-per-minute pump is the usual step up from the aquarium pump most machines ship with. On plywood, back it off — too much air turns a cut into a bonfire and leaves you with a scorched top face.
Everything that quietly moves the ceiling
- Focal length. A 2-inch lens has a tight focus window and stops helping beyond about 6-8 mm; a 4-inch lens holds a usable spot deep into thick stock.
- Tube hours. A 60W tube at two thousand hours may be delivering 40W. Your thickness ceiling drops with it.
- Mirror and lens cleanliness. A visibly hazy ZnSe lens easily costs 10-20% of delivered power.
- Material moisture. Damp ply steams instead of cutting and can drop your practical maximum by a third.
- Bed flatness. A bowed sheet is a moving focus, and the cut fails wherever the sheet lifts.
- Ambient temperature and chiller performance. CO2 tube output falls as coolant temperature climbs; a hot workshop in August is a genuinely lower-powered machine.