CO₂ acrylic cutting & engraving
Clear edge, plus masking on/off
Pass · speed/power · air · stock
Melt it clean once — don’t touch it twice
A flame-polished edge happens when the cut line melts and re-flows smooth in a single pass — it’s not a separate finishing step. You get there with four levers: one pass (re-cutting reheats and disturbs an edge that already flowed clean), speed and power tuned to melt, not boil, minimal air disturbance right at the cut line, and cast acrylic, which holds a more consistent edge than extruded. On masking: leave it on through the cut to keep smoke residue and handling scratches off the surface, and only remove or score it where the job calls for it — test on scrap first, because masking type changes the outcome too.
1 · What a flame-polished edge actually is
The 10.6 µm CO₂ beam doesn’t slice acrylic like a blade — it melts a narrow channel through the sheet. If that melt is clean and even, the cut wall re-flows into a smooth, glassy surface as it cools: a flame-polished edge, with no separate polishing step. Get any of the four levers wrong and the same mechanism gives you a frosted, ridged, or boiled edge instead.
- Single pass. A second pass reheats an edge that has already flowed smooth, disturbing the finish it just achieved. If a job doesn’t cut through cleanly on pass one, that’s a sign to adjust speed or power — not to add a pass.
- Speed and power tuned to melt, not boil. Slow enough (or hot enough) to melt the material cleanly through the sheet; not so slow or hot that it boils and bubbles instead of flowing.
- Minimal air disturbance at the cut line. Air assist keeps flame down and clears vapor — but too much of it right at the melt scatters the flow before it can re-flow smooth. See the air-assist section below.
- Cast stock. Cast acrylic holds a more consistent, glossier edge than extruded, which is more prone to unevenness. If the job is sold on the edge, start with cast — see the cast vs. extruded guide for the full trade-off, including how it also decides engraving contrast.
Boss’s own acrylic cutting starting point
Boss’s published CO₂ settings chart lists acrylic (1/4″) cutting at roughly 65–80% power across the 155 W–70 W class, 10–20 mm/s — higher wattage runs less power for the same result. Treat it as the starting window to tune from with a scrap test, not a fixed recipe; lens, bed condition, and sheet grade all shift it.
2 · Air assist: same machine, opposite setting
This is the setting operators most often carry over from the wrong job. Wood and acrylic want opposite air-assist behavior on the same machine, and the CO₂ air assist guide covers the mechanics in full — the acrylic-specific read is below.
| Job | Air assist | Why |
|---|---|---|
| Wood, MDF, plywood | Stronger, steady flow | Wood smokes and chars — good flow clears the plume and keeps the edge lighter. Dark, sooty edges mean insufficient airflow or extraction. |
| Acrylic — standard cut | Moderate, steady | Enough to hold the flame down and keep the cut clean without scattering the melt. |
| Acrylic — max-clarity show edge | Reduced, minimal disturbance | Lets the melt re-flow smooth for the clearest possible edge — but less air also means more flame, so this trades a small fire-risk increase for cosmetics. Stay at the machine and watch it closely. |
Same machine, same air-assist hardware — the acrylic edge you want decides which end of that range you run.
3 · Edge defects and what’s causing them
| Defect | Likely cause | Fix |
|---|---|---|
| Frosting | Too much air disturbance at the cut line, or multiple passes | Drop to moderate/minimal air for the cut; run a single clean pass at tuned speed/power. |
| Striations / ridges | Feed too fast, or power too low for the speed | Slow the feed or raise power in small steps (5–10%) and re-test on scrap; don’t jump straight to a big change. |
| Bubbling / boiling | Too slow or too hot — the material boils instead of melting evenly | Speed up the feed or lower power; the goal is a clean melt, not maximum heat. |
| Marks on the back of the part (flashback) | Beam reflecting off the honeycomb or grid support directly under the cut line | Cut on pins, elevate the sheet off the bed, or switch to a knife-edge support so there’s nothing directly under the kerf to reflect off. |
4 · Masking: what it’s for, and when to lose it
The protective masking on both faces of a sheet isn’t packaging — it’s part of the process. It keeps hot, corrosive cutting vapor and normal shop handling from marking a surface that would otherwise be flawless off the bed.
- What it protects against. Smoke and vapor residue during the cut, and scratches from handling, nesting, and shipping before the part is done.
- Paper vs. film. Paper masking resists fusing to the edge and shields the surface well for general work. Non-adhesive, laser-cuttable PE film gives the cleanest result on a show edge, since it leaves no adhesive residue at the kerf.
- Leave it on when the surface needs protecting through the whole job — during the cut itself, and through any adjacent engraving, handling, or shipping before the part is finished. Peel it only once the part is done and inspected.
- Remove or score it when the job specifically calls for exposing acrylic at that point — for example, scoring and weeding the mask on just the area being engraved so the rest of the sheet stays protected. Light-adhesive masks can lift where the beam idles or on tight radii; add lead-ins or switch to paper/film mask for those parts.
- Test on scrap first. Mask type and adhesive strength change how it behaves at speed, on curves, and at cut edges — confirm on the same sheet before committing a full nest.
Wrinkled or lifted mask is a common frosting cause
A mask that isn’t flat against the sheet traps hot gas under it near the cut line, which shows up as hazy, etched surface right next to a clean cut. Press down or replace any lifted mask corner before running the job.
5 · Post-finish options — when the laser edge isn’t quite enough
Flame polishing with a torch
A quick pass of an oxy-fuel or propane flame can touch up minor haze on an already-decent edge. Use it like a scalpel, not a blanket fix — it’s a fast, localized reheat, and reheating an edge changes the stress in it. [VERIFY with Boss] If the part will later be solvent-cemented, some cements are more prone to crazing a re-stressed, flame-polished edge — test the specific cement on a scrap piece finished the same way before committing a production run.
Wet sanding for saw-cut or rough edges
For edges that were never going to flame-polish clean — saw-cut stock, or an edge you deliberately ran cool and low-stress — progressive-grit wet sanding followed by buffing gets you a comparable finish without the extra heat a torch adds.
Frequently asked
Acrylic edge finish & maskingQWhy are my acrylic edges frosted instead of clear?
Almost always too much air disturbance at the cut line, or a second pass over an edge that already flowed clean. Drop to a moderate or minimal air setting for the cut, run a single pass at speed/power tuned to melt (not boil) the material, and re-test on scrap.
QShould I leave the masking on while I cut?
Yes. The mask on both faces protects the surface from hot, corrosive vapor during the cut and from handling scratches afterward. Leave it on through the whole job and peel it once the part is inspected — a wrinkled or lifted mask is a common cause of hazy surface marks near the cut line.
QWhy do I get marks on the back of my cuts?
That’s flashback — the beam reflecting off the honeycomb or grid support directly under the kerf. Cut on pins, elevate the sheet off the bed surface, or switch to a knife-edge support so nothing sits directly under the cut line.
QDoes more air assist mean a cleaner acrylic cut?
Not for a clear edge — it’s the opposite of wood. Wood wants strong, steady air to clear smoke and char. Acrylic cut for a clear, flame-polished edge wants moderate to minimal air disturbance right at the cut line; too much air frosts the edge and fans the flame. Same machine, opposite setting.
QCan I flame-polish a laser-cut acrylic edge with a torch?
Yes, as a light touch-up on an edge that’s already close — treat it like a scalpel, not a fix for a badly frosted cut. Reheating the edge changes its stress state, so if the part will be solvent-cemented afterward, test that specific cement on a scrap piece finished the same way first. [VERIFY with Boss]
6 · Related guides & next steps
- Acrylic — how the beam interacts with acrylic, in the Learn library.
- Cast vs. extruded acrylic — the stock choice behind edge consistency and engraving contrast.
- CO₂ air assist guide — the full mechanics of air assist across materials, wood included.
- Choosing a CO₂ laser lens — how lens choice affects cut-edge quality and engraving detail.
Chasing a specific edge or finish spec?
Get the settings dialed on the right machine.
Flame-polished, frosted engrave, or a saw-clean edge you’ll sand — the result starts with the platform. Tell a Boss Laser specialist the material, thickness, and finish you’re after, and we’ll point you to the right CO₂ system.