Lasering acrylic: cast or extruded, diode or CO₂?
are explained briefly when you hover over or tap them.
Acrylic (PMMA) is the most important material for lasers after wood. With a CO₂ laser you get glossy cut edges and white engravings. With a diode laser much less is possible, and the colour of the sheet decides whether anything happens at all.
Cast (GS) and extruded (XT)
Acrylic comes in two manufacturing types. Cast acrylic (GS) is poured between sheets, extruded acrylic (XT) is pressed through a die. For the laser this makes a real difference.
| Cast (GS) | Extruded (XT) | |
|---|---|---|
| Engraving | bright, frosty white, high contrast | matt grey to almost clear, little contrast |
| Cut edge | clean and burr-free, but less glossy | flame-polished, so smooth and glossy |
| Thickness tolerance | about ±15 % | about ±5 % |
| Power required | higher | lower, cuts faster |
| Price | higher | cheaper |
The values for tolerance and edge appearance come from the material notes from Trotec and Epilog. This gives a simple rule of thumb: GS for engraving, XT for cutting. For signs with white lettering you use GS. For parts with plug-in joints, XT is often more practical because of the tighter thickness tolerance.
The manufacturing type is usually printed on the protective film or in the data sheet. If you do not know it, engrave a small test patch: frosty white points to GS, clear or grey to XT.
Colour and diode lasers
A diode laser works with blue light at around 450 nm. Clear acrylic lets this light pass almost unhindered, so it is not absorbed and cannot heat anything. The beam is also refracted and does not form a clean focal point. Blue acrylic also lets blue light through. xTool states explicitly in its support pages that clear, white and blue acrylic cannot be cut with the blue diode.
Dark, opaque sheets, on the other hand, work well:
| Acrylic | Diode laser | CO₂ laser |
|---|---|---|
| black, opaque | good, engraving and cutting | good |
| dark colours, opaque | mostly good, test | good |
| white, opaque | poor | good |
| red, yellow, green, opaque | very variable, test | good |
| blue | not suitable | good |
| clear or transparent tinted | not suitable | good |
Manufacturers therefore almost always state the cutting capacity for black acrylic. Two examples from the device overview: the Creality Falcon2 22W with up to 10 mm black acrylic, the xTool S1 40W with up to 15 mm, each in one pass. If you want to cut clear acrylic regularly, there is no way around a CO₂ laser. Why this is so is explained in Laser types compared.
Cutting with CO₂
A CO₂ laser works at 10,600 nm. Acrylic absorbs this wavelength well in every colour, including clear. According to the manufacturer, the xTool P2S with 55 W cuts up to 20 mm of clear acrylic in one pass.
A few points matter for a nicely glossy edge:
- Little air: Too much air assist cools the edge too quickly and it turns milky. Trotec recommends 0.2 bar or less for acrylic where possible. When cutting you still need some air so that no flames form.
- Not too slow: A very low speed makes the kerf wide and increases the fire risk.
- Frequency: If your machine lets you set a pulse frequency, Trotec gives about 5,000 to 20,000 Hz for GS and up to 5,000 Hz for XT. Many hobby CO₂ lasers with a glass tube do not have this setting.
- Support: From about 6 mm thickness, a slat bed is better than a honeycomb bed, because reflections from below otherwise roughen the edge.
- Protective film: Leave it on when cutting, it protects the surface from smoke deposits. Peel it off afterwards.
As a rough rule of thumb, Trotec gives about 10 W of laser power per millimetre of material thickness. A 40 W laser can therefore manage around 4 mm at a good speed, and thicker sheets go slower or in several passes.
Engraving
Engravings need little energy. A light surface engraving on GS gives the best contrast, too much power makes the engraving grey and rough. Peel off the protective film for engravings.
A proven trick with clear acrylic is engraving from behind: you mirror the motif and engrave the back. Seen from the front, the engraving then sits protected behind the sheet and looks deeper. For illuminated signs with an LED base this is the standard.
With a diode laser you engrave only opaque, dark sheets. This removes the colour layer and produces a light, slightly matt contrast.
Starting values
Rough starting values for 3 mm acrylic. They are a guide for your test grid, not ready-made settings.
| Task | 10 W diode, black | 20 W diode, black | 40 W diode, black | 40 to 55 W CO₂, all colours |
|---|---|---|---|---|
| Engraving | 30 to 50 %, 100 to 200 mm/s | 30 to 50 %, 200 to 400 mm/s | 40 to 60 %, 300 to 500 mm/s | 15 to 35 %, 300 to 500 mm/s |
| Cut 3 mm | 100 %, 2 to 4 mm/s, 2 passes | 100 %, 4 to 8 mm/s, 1 to 2 passes | 90 to 100 %, 10 to 25 mm/s, 1 to 2 passes | 60 to 85 %, 10 to 25 mm/s, 1 pass |
For comparison: for 3 mm black acrylic on the 10 W M1, xTool gives as a reference 100 % power, 3 mm/s and two passes. How to turn the ranges into a test grid is explained in Material test.
Safety
Acrylic burns readily and with a barely visible flame. When cutting, a small flame can form on the edge and persist. Never leave the laser running unattended and keep a fire extinguisher ready. The smoke smells pungent, extraction to the outside is necessary.
Make sure you really have acrylic. Polycarbonate looks very similar but cuts poorly, turns yellow to brown and gives off hazardous fumes. PVC sheets can also look like acrylic at first glance. Anything you cannot identify with certainty does not go in the laser. More on this in Prohibited materials.
Continue with: Laser types compared and Material test.