Any Boss CO₂ — LS, HP, EVO
Cast and extruded acrylic (PMMA)
Engrave, then cut
Not the settings — the sheet
Leave the protective mask on both faces, engrave first and cut second, run exhaust the whole time, and prove the settings on a scrap of the same sheet before you commit a nest. Boss publishes 80/75/65% at 10–20 mm/s for cutting ¼″ and 25/20/15% at 350 mm/s for engraving, read down the column that matches your wattage. Two things catch people out: the sheet decides the engraving, not the settings — extruded acrylic will never frost white no matter what you do to it — and the glossiest edge carries the most hidden stress, which is why a perfect part can craze days later when someone cleans it with the wrong thing.
1 · Before the first cut
Acrylic is forgiving to cut and genuinely pleasant to work with. It is also a combustible plastic, and the machine does not know the difference between it and the sheet of unknown plastic that came in the same delivery.
- Never run it unattended. A small dancing flame at the cut point is normal on acrylic. A steady, standing flame is not — that is a fire starting, and acrylic keeps burning once lit. Keep an extinguisher within reach of the machine, not across the shop.
- Exhaust runs on every job, without exception. Cutting acrylic releases vapour that has to be pulled away from the operator. This is a separate job from air assist, which is about the cut itself.
- The enclosure is what keeps the beam contained. Ordinary safety glasses are not rated for this wavelength — they carry no certified optical density at 10.6 µm, and they are not a substitute for the machine being closed. Keep the lid shut whenever the machine is running, and treat a pass-through slot or a defeated interlock as an open beam path. If you ever have reason to work with the path open, use eyewear specifically rated for 10.6 µm at the correct optical density.
The sheet that ends the job early
Polycarbonate looks like acrylic and is not acrylic. Sold as Lexan, it is often stacked on the same rack in the same thicknesses. Under a CO₂ beam it absorbs the wavelength badly, discolouring and scorching rather than parting, so it will not give a clean cut edge. Engraving it is workable; cutting it is not. PVC and vinyl are worse and must never go in the machine at all: they release hydrogen chloride, which becomes hydrochloric acid in the moisture of your lungs and on every metal surface inside the machine. That is operator harm and a machine corroding from the inside out, and no setting, extraction rig or thickness makes it safe. If you cannot confirm a sheet is PMMA, do not cut it — ask the supplier for the SDS, and if that does not arrive, treat the answer as no.
2 · What you need on the bench
| Item | What to use | Why it matters |
|---|---|---|
| Material | Cast or extruded acrylic with protective masking on both faces | The mask is part of the process, not packaging — it stops hot gas from etching the surface along the cut line. |
| Exhaust | Blower running, ducting clear | Pulls vapour out of the machine and away from you for the whole cut. |
| Air assist | On — but gentle (see section 4) | Keeps the plume out of the beam and off the lens. Acrylic is the one material where more is not better. |
| Lens | 2″ for general work; shorter focal length for fine engraving detail | The 2″ is the do-everything choice. Choosing a CO₂ lens covers the trade-off properly. |
| Bed | Clean honeycomb or knife bed, flat | Flatness holds focus across the sheet; honeycomb lets air and vapour escape below the cut. |
| Scrap of the same sheet | Offcut from the stock you are about to run | Not from last week’s stock. Grade and thickness vary between deliveries, and the test is only worth anything on the material you are actually cutting. |
3 · Pick the sheet before you pick the settings
This is the decision that decides the job, and it is made at the supplier rather than at the machine. Cast acrylic engraves to a bright frosted white. Extruded acrylic engraves nearly clear. Both cut beautifully, so cut quality will not tell you which one you bought — the engraving will, and by then the part is made.
- Selling the engraving? Awards, plaques, donor walls, anything where the graphic has to read across a room — cast.
- Selling the cut? Faceplates, boxes, inlays, tab-and-slot assemblies, anything where parts have to fit each other — extruded, which holds a tighter thickness tolerance and usually costs less.
- Don’t reflexively buy clear cast. Impact-modified sign grade survives fabrication and installation better for illuminated signs; satin and matte sheet gives a frosted-glass diffuser look without engraving it; edge-lit sheet is engineered to glow from LEDs at the edge and may need almost no etching at all. The higher-margin job is frequently not clear cast.
Full detail on how the two are made and how to tell an unlabelled sheet apart: cast vs extruded acrylic.
4 · Boss’s published acrylic settings
These are transcribed from Boss’s own BL2-T83 material settings charts for the CO₂ platform — first-party numbers, not industry averages. Power is a percentage at each wattage tier; read down the column that matches your machine.
| Job | Power % at 70 W / 105 W / 155 W | Speed | Scan gap | Thickness |
|---|---|---|---|---|
| Cutting | 80 / 75 / 65 | 10–20 mm/s | — | ¼″, single pass |
| Engraving | 25 / 20 / 15 | 350 mm/s | 0.065 mm | any |
On an EVO: the published charts start at 70 W and the EVO ships a 60 W tube, so it has no column of its own — start from the 70 W figures, expect to run a little slower, and prove it on scrap. Where a speed is a range, the faster end pairs with the higher wattage. Boss publishes up to ¼″ — thicker acrylic is cut all the time with more power, slower speed and multiple passes, but there is no published figure for it, so we do not print one.
Acrylic is the one material that wants less air
On every other material, the answer to a rough or charred edge is more air assist. On acrylic it is often the opposite. That clear flame-polished edge is molten acrylic re-flowing and freezing smooth, and too much air at the cut line cools it early and frosts it. Keep air assist on — it protects the lens and keeps the plume out of the beam — but turn it down and watch the edge rather than reaching for the regulator. Know what you are trading: less air at the cut line means more flame, and acrylic keeps burning once lit — so run a gloss setting attended, with the exhaust working properly. CO₂ air assist covers pressure properly.
The complete Boss charts — wood, paper, leather, glass, stone and coated metals — are in CO₂ laser settings by material.
5 · The procedure
- Confirm the sheet and leave the mask on. Verify it is PMMA, not polycarbonate. Check both faces are masked and press down any lifted corner — a wrinkle is where hot gas gets underneath and etches the surface.
- Nest the file, engrave layer separate from cut layer. Arrange parts to use the sheet, and keep engraving and cutting as distinct operations so you control their order. Apply your saved kerf compensation now if the parts have to fit each other.
- Fixture and focus. Set the sheet at a known zero, flat and unable to shift. Set focus to the top surface. An out-of-focus beam cuts wide and rough and is the most common cause of an edge that will not come clean no matter what you do to the power.
- Stay between 5% and 95% power. Below about 5% the tube will not fire at all; above 95% you shorten tube life for very little gain. A job that needs more than 95% needs a slower speed or a second pass instead.
- Test on scrap first — always. Run a small square of the real job on an offcut of the same sheet: engrave patch, cut line, one inside corner. Check that it cut through, that the engrave has the contrast you expect, and that the corner is not burned. Change one variable at a time in 5–10% steps. Five minutes here saves a full sheet.
- Engrave first, then cut. In that order, always — once a part is cut free it can shift, and an engrave onto a moved part is scrap. Exhaust on throughout, and stay with the machine.
- Inspect before you peel. While the parts are still masked and still on the bed, check that everything cut through, look at the inside corners, and look for haze near the cut lines. A problem found here is a re-run; a problem found after assembly is a remake.
- Peel, clean gently, finish only if it needs it. Mild soap and lukewarm water. Most of the time the laser edge is already better than anything you would do to it — polish only when it genuinely is not good enough.
6 · The beautiful edge problem
This is the part of acrylic work that costs people real money, and it is invisible on the day.
More energy at a given speed gives a glossier edge — and more stress in the material just behind it. That stressed zone sits a few hundredths of an inch deep, it looks like nothing, and it stays quiet until the part meets a solvent or a load. Then it crazes: a network of fine cracks that appears days or weeks after a part shipped clean. The customer cleaned it with glass cleaner, or the assembly was solvent-bonded, or the part was bent into a fixture.
So match the edge to the part’s future, not to how it looks on the bench:
- A display part that will be looked at and dusted — run it glossy. This is what acrylic is for.
- A part that will be solvent-bonded, bent, tapped, or cleaned hard — run cooler and faster for a lower-stress edge, accept the slightly duller finish, and anneal before the downstream step. Annealing means holding the finished part at a moderate, controlled temperature and then cooling it slowly, which lets that stressed zone relax instead of holding tension until a solvent finds it — your sheet supplier publishes a schedule for their own grade, and that is the one to follow.
- Segregate the stress-sensitive parts in QC and qualify them separately. They are a different product from the display parts even when they came off the same sheet.
One bad wipe-down can crack a perfect part
Acrylic is cleaned with mild soap or detergent and lukewarm water. Not glass cleaner, not ammonia, not alcohol, not solvent. Those attack PMMA on their own, and a laser-cut edge is already more stress-sensitive than a sawn one — which is why this is worth putting on the care card that goes out with the part, not just in your own shop notes.
7 · Troubleshooting
| Symptom | Likely cause | Fix |
|---|---|---|
| Engraving looks clear or weak, and no amount of power fixes it | Extruded acrylic where the job needed cast | Change the stock, not the settings. Extruded does not frost white. Re-test on a cast offcut before blaming the machine. |
| Edge is frosty when you wanted it glossy | Too much air at the cut line, or too little energy | Turn air assist down first — this is the acrylic-specific one. Then raise energy carefully, watching the stress trade-off. |
| Part crazes days later after cleaning or bonding | Edge stress from a hot, glossy cut meeting a solvent | Run cooler and faster on stress-sensitive parts; anneal before bonding; specify mild soap and water on the care card. |
| Burned or over-melted inside corners | The head slows at corners and keeps dumping the same energy into less distance | Add lead-ins, drop power or pulse on tight radii, and tie frequency to distance rather than time if your controller supports it. |
| Marks on the back of an otherwise clean part | Flashback — the beam reflecting back off the honeycomb directly under the kerf | Raise the sheet off the bed on pins, or use a knife-edge support. Check the bed is clean while you are there: debris in the cells reflects more than bare honeycomb does. |
| Hazy or etched surface near the cut line | Mask wrinkled, lifted, or not in contact with the sheet | Re-mask with good top-surface contact; keep exhaust strong so hot gas is carried away rather than pooling. |
| Mask lifts at start points or on tight curves | Light-adhesive film plus dwell time where the head idles or turns | Add lead-ins, reduce power in curves, or switch to paper mask for that job. |
| Standing flame at the cut, smoke inside the cabinet | Too much power for the speed, or exhaust not moving enough air | Stop the job. Raise speed and drop power to the least that still cuts through, and check the blower and ducting before restarting. |
| The same job gradually needs more power than it used to | Optics drifting dirty, or alignment moving | Clean the optics and check alignment. Parameter drift over weeks is the early warning, and it is worth logging. |
8 · What to check, and what to write down
- First-article dimensions — overall size plus any slot or tab fit, before the full nest runs.
- Kerf, logged per material and thickness — the compensation that made the parts fit is worth more than the parts. Write it down against the stock, not in your head.
- Inside corners — localised melt or burn, on the first part and the last.
- Top surface near cut lines — trapped-gas etching, checked before the mask comes off.
- Show edges — adhesive residue from the mask.
- Stress-sensitive parts — pulled out and qualified separately.
Saving a working recipe by name — material, grade, thickness, power, speed, air setting, kerf — is what turns a good result into a repeatable one. The recipe is the asset; the part is just this week’s output.
Frequently asked
Cutting & engraving acrylicQWhy does my acrylic engraving look clear instead of white?
You are almost certainly running extruded acrylic. It engraves clear to light grey rather than frosting white, and that is a property of how the sheet was made — no power or speed setting recovers it. Switch to cast acrylic for the bright, high-contrast look, which is the whole point of most engraved acrylic work. If you are not sure which you have, engrave a corner of an offcut: cast frosts white immediately.
QHow many watts do I need to cut acrylic?
Less than most people assume, because acrylic cuts willingly. Boss publishes cutting figures for ¼″ acrylic across the 70 W, 105 W and 155 W tiers — every one of those machines does the job, the higher tiers simply do it at a lower power percentage and a faster feed. More wattage buys you speed and thickness, not a better edge. The thing you actually outgrow first is usually the bed, not the tube — if you are pre-cutting sheets down by hand to make them fit, that is the constraint talking.
QDo I really have to leave the masking on?
Yes, and it is the single cheapest quality improvement on this material. The mask stops hot gas from the cut settling on and etching the surface next to the cut line — the hazy band people blame on the lens or the exhaust. Leave it on both faces, press down any lifted corner before you start, and do not peel it until after you have inspected the parts on the bed. For show edges where mask residue would be a problem, a non-adhesive laser-cuttable film leaves nothing behind.
QWhy did my part crack a few days after it was cut?
Hidden edge stress meeting a solvent. A hot, glossy cut leaves a stressed zone just behind the edge that looks perfect and stays quiet until something acts on it — glass cleaner, a solvent-bonded joint, or the part being flexed into place. Then it crazes into fine cracks. The fix is upstream: run cooler and faster on any part that will be bonded, bent or cleaned hard, anneal before that step, and tell the end customer to clean it with mild soap and water. This is the most common expensive surprise on acrylic.
QShould I engrave first or cut first?
Engrave first, every time. Once a part has been cut free it is sitting loose on the bed — it can lift on the air, drop into the honeycomb, or shift a fraction — and an engrave onto a part that has moved is scrap. Engraving while the sheet is still whole also means the sheet itself is holding everything in register. Keep the two as separate operations in your file so the order is yours to control rather than the software’s.
QCan I use my wood settings on acrylic?
No, and it is worth understanding why rather than just avoiding it. Wood chars — it burns and leaves carbon — so wood recipes are built around clearing heat aggressively. Acrylic melts and re-flows, which is where the glossy edge comes from, so the same aggressive settings over-pulse it, burn the corners and put stress in the edge. Build a separate acrylic recipe library. The two materials want opposite things from air assist alone.
QCan I cut polycarbonate the same way?
No. Polycarbonate (Lexan) sits on the same rack in the same thicknesses and looks the same, but it absorbs the CO₂ wavelength badly — it discolours and scorches instead of parting, so it will not give a clean cut edge. Engraving it is workable; cutting it is not. It is not the safety emergency PVC is, but it is wasted material and a smoky cabinet. PVC and vinyl are the genuine hazard: they release hydrogen chloride, which harms the operator and corrodes the machine internally, and nothing makes them safe to run. If a sheet cannot be confirmed as PMMA, do not put it in the machine.
9 · Related guides & next steps
- Acrylic — the material behaviour behind these settings, in the Learn library.
- Cast vs extruded acrylic — the stock decision in full, including how to identify an unlabelled sheet.
- Acrylic edge finish & masking — the four levers on edge quality, and when to leave the mask on.
- CO₂ laser settings by material — Boss’s complete published charts.
- CO₂ air assist — pressure, and the water-and-oil problem that quietly kills lenses.
- Choosing a CO₂ laser lens — focal length for fine engraving against cutting depth.
- Acrylic & plastics applications — what people build with this material, and which machine suits the mix.
- Personalization & custom products — selling acrylic awards, gifts and engraved work, and what the product mix does to the machine choice.
Sources
Cutting and engraving power, speed and scan-gap figures are transcribed from Boss’s own BL2-T83 CO₂ material settings charts (70 / 105 / 155 W tiers) — first-party Boss data, and the same numbers published on CO₂ laser settings by material. The focus rule and the 5–95% power limit come from the Boss HP Series User Manual, as does the do-not-laser list. That PVC releases hydrogen chloride and must never be lasered is documented Boss guidance and industry consensus. Cast-versus-extruded behaviour, edge stress and crazing, masking practice and annealing are settled acrylic fabrication practice, consistent with the technical guidance published by the major PMMA sheet manufacturers. Every setting here is a starting point: grade and thickness vary between deliveries, which is why the procedure tests on scrap from the sheet in front of you.
Working out which machine suits the work?
Acrylic asks for bed size and control, not raw wattage.
Tell a Boss Laser specialist what you are cutting, how thick, and how big the sheets are — we will size the bed to the stock rather than sell you power you will not use.