Laser air assist

What air assist does

LightBurn’s manual describes it plainly: air assist blows air onto the material at the spot where the beam strikes, and it can help prevent soot build-up and charring, and aid in cutting. On a diode laser that usually means a small pump, a tube and a nozzle around the beam; CO2 machines often have it built in.

1. Moves the smoke. Thunder Laser says air assist removes smoke and reduces charring, for smoother cut edges.
2. Keeps the lens clean. Thunder Laser: it stops debris and smoke getting into the laser head and lenses. xTool’s D1 Pro manual says the same of blowing away smoke and air-borne debris.
3. Lowers the chance of flames. Epilog designs air assist to remove heat and combustible gases from the work surface, and calls it absolutely essential when cutting acrylic.
4. Helps thick cuts. Thunder Laser says high-pressure air brings more oxygen to the cut, for faster cutting of thicker material, and some maker cut figures assume it (Sculpfun’s S40 Max: 20 mm plywood in one pass with its 50 L/min pump). Sculpfun’s S30 Ultra page says cutting is “more than 5 times faster” than without air assist, but gives no conditions or test method, so we do not use that figure.

For how deep a laser cuts with and without help, see how thick can a laser cut; for settings by material, the material pages.

Why cutting and engraving want different air

Every maker that gives settings separates the two. xTool’s M1 Ultra guide puts the knob at MAX for cutting and at level 1 for engraving when you adjust by hand, and its software defaults are 4 and 1. On the P2 and P2S CO2 lasers the built-in pump is set in per cent, separately for cutting and engraving, and xTool says to raise it for cutting and lower it for engraving (at least 30 % on the P2, 10 % on the P2S). Thunder Laser’s CO2 machines have two air stages, Cut and Engrave, each with its own needle valve.

Why gentle for engraving? Thunder Laser’s answer is that excessive airflow can distort the engraved pattern. A little air still keeps smoke off the lens; owners on the LightBurn forum disagree about how much, which is opinion rather than a maker figure.

Clear acrylic on a CO2 laser is the exception for cutting. Trotec’s acrylic guide asks for compressed air or standard air assist through a large-diameter nozzle at no more than 1.5 psi (0.1 bar), and says negative pressure (downdraft exhaust) matters more than airflow. A 2014 Trotec blog post adds that too much air leaves a bubbly, cloudy edge. More on the acrylic page; a blue diode cannot cut clear acrylic at all (diode vs CO2 vs fiber).

Maker air assist pumps, side by side

Hobby air assist is sold by flow, in litres per minute; makers rarely say how it was measured. Here is what each maker publishes. We have not measured any of these. On 2026-11-02 several maker stores refused our requests, so rows marked “maker’s listing only” come from the product title or a search excerpt of the maker’s own page, not a full read; check the live page before you buy.

“Maker’s listing only” = the product title or a page excerpt, not a full read. Flow and pressure are the makers’ figures; pressure is the maximum, where given.

Affiliate links: the AtomStack, Sculpfun and TwoTrees product links in this table go through Awin, and we may earn a commission if you buy, at no extra cost to you. We have not tested these products.

Where to get air assist

AtomStack and Sculpfun sell their air assist on their own stores. Compare the listed flow with the table above; for a lot of cutting, the larger pumps (50–60 L/min) are what the makers pair with their bigger lasers (see the AtomStack and Sculpfun machine pages).

The math behind the calculator

These are the standard nozzle equations for air (γ = 1.4, R = 287 J/kg·K; p₀ is the absolute pressure behind the nozzle, pₐ the air outside). The assumptions are ours: a discharge coefficient C_d of 0.8, 20 °C, sea-level air, no loss in the tubing, and a straight line between the two ratings on the pump box. Real pumps, hoses and nozzles differ, so use the results to compare options, not to predict a cut. Units: 1 CFM = 28.317 L/min, 1 psi = 6.895 kPa, 1 bar = 100 kPa, 1 MPa = 1,000 kPa.

Pump or compressor at a glance

xTool’s P2 and P2S cannot use an external pump at all: xTool says the built-in pump has to talk to the mainboard in real time.

Setting up Air Assist in LightBurn (M8 and M9)

LightBurn does not blow the air; it sends a signal at the start of each layer. If your pump has only a power switch, LightBurn’s manual says the Air switch has no effect either way, and you switch the pump yourself.

1. 01
   Check the pump can be switchedAutomatic kits are switched by the controller; Sculpfun’s automatic kit for the S9 and S10 is switched with M8 in LightBurn. A pump with only a power switch is not.
2. 02
   Pick M7 or M8Device Settings › Other Options › GCode Devices › Air Assist chooses whether LightBurn uses M7 or M8. In the original Grbl for the Arduino Uno, M8 (flood) is on pin A3 whatever the M7 setting; M7 (mist) works only if the firmware was compiled with it. Other boards and firmware map pins their own way.
3. 03
   Turn Air on per layerIn Cuts / Layers, toggle Air for each layer, or right-click the column header to enable, disable or invert all. Cutting layers on; engraving layers on with the knob low, or off.
4. 04
   Know what is sentM8 (or M7) when a layer with Air on starts. LightBurn staff say on its forum that M8 and M9 are the Air Assist functions for GRBL, and that a layer with Air off makes LightBurn send M9 to turn the air off — so leave Air on for every layer if you want it to stay on. A forum user adds that M9 stops M7 too.
5. 05
   Galvo and RuidaGalvo lasers have no Air switch in LightBurn. LightBurn’s manual does not cover wiring air to Ruida controllers; follow your machine maker’s manual.

Before the first job: test on a small piece of scrap, stay with the machine, and watch that the air comes on and off when it should. If it does not, the signal is not reaching your pump: check the M7 / M8 setting and your kit’s wiring guide. A controller pin only gives a signal; do not wire a pump straight to it. If you also changed $32 laser mode or other Grbl settings, check them with our Grbl $$ checker.

Burn marks on the back: the honeycomb bed

Once the beam is through, the light that leaves the bottom hits whatever is underneath. Trotec says reflections on the back must be avoided as much as possible. Its table range shows the trade-offs: honeycomb for jobs that need minimal back reflection, an acrylic cutting grid designed to prevent it, and slat (lamella) tables where you remove slats to change the support points. Epilog says its vector cutting grid dramatically reduces underside reflections and removes smoke.

1. Raise the work. Trotec: increasing the distance between the material and the table also helps. It cuts small acrylic holders that sit in the grid of its table.
2. Use slats for big or thick parts. Trotec’s acrylic guide: for parts over 100 mm or thicker than 6 mm, a table with acrylic lamellas generally gives the best results.
3. Keep the honeycomb flat and clean. Lotus Laser, which makes slat tables, says a bent honeycomb can itself cause back reflection and cannot be cleaned; bear in mind that it sells the alternative.
4. Do not overshoot. Every pass after the cut is through sends light straight to the bed. Find the fewest passes that cut through with a test on scrap, for example with our material test generator.
5. Let the smoke out underneath. Air assist pushes smoke down through the cut; a bed that lets it escape keeps the underside cleaner, which is one reason Epilog’s grid “removes smoke”.

Enclosures, exhaust and fire

Air assist moves smoke around; it does not take it out of the room. Laser makers ask for exhausts of 150 CFM at pressure (Universal Laser Systems desktop) to 350–400 CFM (most Epilog machines), against about 1 CFM added by a 30 L/min pump. Size the fan and duct with our exhaust fan calculator, and keep it running after the job until the enclosure has cleared. Check that the material is safe to laser at all on what not to laser cut.

Air assist lowers the chance of flames; it does not remove it. Epilog: never allow your laser system to run unattended. Keep a fire extinguisher at hand, and keep some air on when cutting acrylic, which Epilog calls one of the most flammable materials that can be laser cut.

FAQ

Do I need air assist for a laser engraver?

For cutting, makers treat it as standard. xTool’s M1 Ultra guide sets its air knob to MAX for cutting, Sculpfun ships 30–50 L/min pumps with its larger lasers, and some cut figures assume it: Sculpfun’s 20 mm plywood in one pass on the S40 Max is with its 50 L/min pump. For engraving it matters less and makers keep the air low. LightBurn’s manual says air assist can help prevent soot and charring, and aid in cutting.

What air flow or pressure do I need for laser air assist?

Hobby diode pumps are sold by flow: the maker figures we found run from 25 to 60 L/min. Longer lists 0.03 MPa (30 kPa) for its 30 L/min kit; the 50–60 L/min pumps give no pressure. The pumps built into xTool’s CO2 machines are rated by pressure, up to 200 kPa on the P2S. For flame-polished clear acrylic, Trotec asks for at most 1.5 psi (0.1 bar). What reaches the work also depends on the nozzle hole, which the calculator on this page works out.

Should air assist be on when engraving?

Usually on, but low. xTool’s software default is 1 for engraving against 4 for cutting, and Thunder Laser warns that excessive airflow can distort the engraved pattern. A little air still keeps smoke away from the lens.

Can I use an air compressor for laser air assist?

Yes, and Thunder Laser suggests one if most of your work is cutting. Fit a regulator, a water trap and a filter, and check the plumbing: Epilog notes that a laser set up for a constantly running diaphragm pump can keep venting a compressor’s tank, so the motor never stops. xTool’s P2 and P2S cannot use external pumps.

Sources

• LightBurn documentation — Cut Settings for beginners (the Air switch)
• LightBurn documentation — Device Settings › Basic Settings (Air Assist: M7 or M8)
• LightBurn documentation — Cuts / Layers window (per-layer Air, Gantry lasers only)
• LightBurn forum — LightBurn staff: M8 and M9 are the “Air Assist” functions for GRBL
• LightBurn forum — LightBurn staff: leave Air Assist on for all layers, or LightBurn emits M9 to turn it off
• Grbl — config.h (M7 mist disabled by default; M8 flood on pin A3 of the Arduino Uno)
• Grbl wiki — v1.1 commands (coolant state M7, M8, M9)
• xTool support — M1 Ultra Air Assist Set knob (article 1464)
• xTool support — P2 air pump settings (article 775)
• xTool support — P2S air pump (article 1683)
• xTool D1 Pro user manual, page 5 (copy on ManualsLib)
• Thunder Laser — Dual air-assist system
• Epilog Laser — Air assist: default to shop air conversion
• Epilog Laser — Laser system features white paper
• Trotec Laser — Acrylic processing guide: how to achieve flame-polished edges (PDF)
• Trotec Laser blog — Laser cutting acrylic for flame-polished edges (Chris Cudmore, 2014)
• Trotec Laser — Acrylic distance holders (back reflections)
• Trotec Laser — Cutting tables (honeycomb, acrylic grid, slats)
• Lotus Laser — Laser cutting on a honeycomb table (a maker of slat tables)
• STYLECNC (a CNC machine maker’s blog) — Laser air assist guide (water and oil in compressed air)
• Pump figures: the maker pages linked in the table above. Sculpfun S40 Max cut figure: our cut thickness sources. Exhaust figures: our exhaust fan calculator sources.

Last checked 2026-11-02 · Maker figures, LightBurn and Grbl documentation, and our calculation; no machine was tested to make this page.