How much air assist do you need? (why more is not better)

Air assist is the third important setting on a laser machine after power and speed. Just like speed and power it is a sweet spot mechanic, where more is not automatically better.

What air assist is actually doing

Air assist is a constant stream of air that is pushed through the nozzle, around the beam, onto the cut point. It is doing three separate jobs at once:

1. Clearing the plume. Smoke and vapour sitting in the beam path scatter and absorb the beam. Blow them out of the way and more of the beam reaches the material.
2. Suppressing flame and char. It cools the edge and displaces the oxygen feeding any flame, which is both a quality benefit and a fire-safety one.
3. Protecting the lens. It keeps vapour and spatter from drifting up into the lens.

Why more is not automatically better

More air cools faster, and that has to be compensated for in the production process, either by slowing down or by increasing power. Too little air, on the other hand, increases the risk of fire. On some materials such as acrylic, cooling the edge too quickly creates bubbles along the cut, giving it a matte texture instead of a transparent one. The amount of air is a balance between fire risk, the edge you want, production speed and the material.

Acrylic wants less air than you think

The reason acrylic cuts with a glossy edge on a CO₂ laser is that the edge melts and re-flows. That is a thermal process, and it needs to happen gently.

Blast it with high-pressure air and you chill the molten edge too quickly. Instead of flowing smooth and clear, it sets rough and frosted. The fix is to turn the air down, not to clean the lens or change the power.

So on acrylic, use just enough flow to clear the smoke and keep the flame down, and no more. For most operations that is around 0.2 to 0.4 bar.

Wood and board want more

The opposite problem. Too little air on wood, plywood or MDF and the smoke does not get cleared out of the kerf. It settles and bakes onto the surface as a brown residue, and the edge chars more heavily.

For most wood, and especially thicker material, use considerably more: roughly 1 to 2 bar, with around 2 bar the usual figure for cutting thick wood.

Stay below 8 bar

Whatever you set at the nozzle, the input pressure from a compressor into the machine must stay below 8 bar. Above that you risk damaging the components in the compressor connection.

Cutting and engraving are different

For engraving you want as little air as possible. The only thing the air has to do there is keep the lens clean and safe. Any air that pushes smoke across the workpiece makes the result worse. Around 0.1 to 0.5 bar gives the best results when engraving.

Removing the lower nozzle, so the air is not blown straight down onto the surface, helps as well. Only do that if it works together with your other layers, such as cutting layers.

Moisture in the air line is an expensive failure

Compressed air carries water, and if the compressor also carries oil, it carries that too. Both travel down the line, out of the nozzle, and onto the underside of the lens, which is warm, and directly in the path.

The result is a lens that fouls quickly, loses power, and in the worst case is damaged permanently. It looks exactly like ordinary dirt, so it usually gets diagnosed as “the lens needs cleaning again” for months before anyone finds the cause.

Fit a water separator

If you are running a compressor, put a water separator, and an oil filter if the compressor is oil-lubricated, in the line before the machine. Drain the compressor tank regularly. This is cheap insurance against a recurring lens problem that is otherwise very hard to diagnose.

Checking air assist is working at all

Before adjusting anything, confirm you have flow:

• Hold your hand under the nozzle while the air is running. On a BRM machine you can use the test mode described below.
• Check the nozzle opening for a blockage. Resin and debris build up there and gradually choke the flow.
• Follow the hose along its whole run for kinks and disconnections, especially where it moves with the head.
• Confirm the pump or compressor is actually running when the job starts.

Weak or absent air assist is a common cause of a machine that has stopped cutting through: my laser no longer cuts all the way through.

On a BRM machine

Setting the pressure

All Pro models have the regulation built in, with an adjustment dial and a readout on the right-hand control panel. Press shift+. on the display and the air runs in test mode so you can set it while you watch the gauge. Turn the big black dial clockwise to increase the pressure and counter-clockwise to reduce it. When the dial is where you want it, press shift+. again to switch test mode off.

On the other models the air system is optional. If it was ordered, it has the same adjustment dial and readout above the right-hand control panel.

Water separators

The BRM models with the compressor option and all BRM Pro models have a water separator built in. They should drain automatically, but check them during weekly maintenance anyway; checking is cheaper than paying for a new lens. See the compressor option.

How the air supply is plumbed

This differs per model. Start with the article for yours:

• BRM Original
• BRM Slim
• BRM Budget
• BRM Pro