My laser no longer cuts all the way through

Your machine cut a material perfectly last month. Today, with the same file and the same settings, it only gets halfway through. Nothing was changed, so what happened?

Almost always, the answer is not that the laser source is worn out. It is one of a handful of causes. Check them in a fixed order: cheapest and most likely first. Working through this list from the top will solve the large majority of cases without spending anything.

Change one thing at a time

The most common mistake is to change the focus, clean the lens, adjust the air and raise the power all in one go. If the problem then disappears you have learned nothing, and you will be back here in a month. Change one thing, run the same test cut, and write down the result.

Use a fixed test cut

Before you start, make yourself a reference test so you can measure progress instead of guessing:

• A small square, 20 × 20 mm, on a scrap of the material that is giving trouble.
• A fixed speed and power that you know used to cut through.
• Cut the same square in five places on the bed: the four corners and the middle.

That last point matters. Whether the problem appears everywhere or only in part of the work area immediately splits the list below into two very different causes.

Does it fail everywhere, or only in one area?

• Everywhere, evenly. Work through steps 1 to 6 below in order.
• Only in one corner or on one side. Go straight to step 4, alignment. Power and settings are not your problem, and tuning them will waste a lot of material.

1. Focus

Focus is the first thing to check because it is free, it takes a minute, and it is the most common cause.

The beam is only at its smallest, and therefore at its most powerful, at one specific distance from the lens. A few millimetres out and the same power is spread over a much larger spot, which cuts noticeably worse. Focus drifts without anyone touching it: the nozzle gets knocked, the lens shaft slips, a focus tool gets lost and replaced with a different one, or the material is simply thicker than last time.

• Re-set the focus with your focus tool for the material you are cutting, or with the autofocus if the machine has that.
• Check the focus tool itself is the right one for the lens that is fitted. A tool for a different focal length will be confidently wrong.
• If the focus tool has gone missing, you can cut a new one: see focus height tools.

If you use the autofocus, rule it out first

Compare the line thickness and the nozzle height against what you normally get. If either has changed, check that the autofocus is working properly.

Related reading: determining focal length and focus distance with different lenses.

2. Dirty or damaged optics

This is the second most common cause and the one people most often mistake for a worn-out laser source. A lens with a haze of smoke residue on it absorbs part of the beam instead of passing it. You lose power, and the lens heats up, which makes it worse.

Check, in this order:

1. The lens. Take it out and look at it under a good light, at an angle. Residue is easier to see as a dull sheen than straight on.
2. The mirrors, all of them, including the one at the laser source.
3. Damage, not just dirt. A lens with a burn pit or a scratch in the coating does not clean up. It has to be replaced.

How to do it: lens cleaning and cleaning mirrors.

If the lens got dirty quickly, find out why

Optics that need cleaning every few days are telling you something else is wrong: usually air assist that is not doing its job, or extraction that is not pulling the smoke away from the cut. Come back to steps 3 and 5 once the cut is working again.

3. Air assist

Air assist blows the smoke and debris out of the cut. Without it, the beam has to burn through its own plume, and the cut gets shallower and dirtier as it goes.

• Put your hand under the nozzle and confirm there is actually air coming out while using the test air mode: shift+..
• Check the nozzle for a blockage. Debris and resin build up in the nozzle opening and slowly choke the flow.
• Check the hose along its whole run for kinks and disconnections, especially near the moving head.
• Listen for the pump or compressor actually running.

See the article for your machine: BRM Original, BRM Slim, BRM Budget, BRM Pro.

4. Mirror alignment

Alignment is the cause behind almost every “it cuts on one side of the bed but not the other” report, and it is very rarely the cause when the problem is even across the whole bed.

The reason is geometry. As the head travels, the distance the beam covers between the mirrors changes. If the beam is not running true down the middle of that path, it walks off-centre as the head moves away, and by the far corner it is clipping the aperture or entering the lens off-axis. You lose power in exactly one part of the work area while the opposite corner still cuts fine.

Alignment drifts after a collision, after transport, after a mirror has been removed for cleaning, and slowly over time as the machine is used.

• Clean the optics before you align. Aligning against a dirty mirror bakes the error in.
• Follow mirror alignment, or mirror alignment for Open Bed machines if that is what you have.
• While you are in there, check that the laser head is still square. A collision can knock it out of perpendicular, which costs power and leaves a shadow line: BRM Original, BRM Pro.

5. The material

Rule out the material before concluding the machine is at fault. Cut a piece of material you have cut successfully before, ideally from a different batch. If that cuts fine, the machine is fine.

Things that make a material cut worse than it used to:

• The sheet is not flat. A warped or bowed sheet lifts away from the bed in the middle, which puts that area out of focus. This produces the classic “cuts round the edges, not in the middle” pattern. Weigh it down or hold it flat.
• Plywood varies enormously, even between sheets from the same supplier and the same order. Internal voids and glue lines are effectively invisible until the beam hits them, and the beam will not get through a glue line that the sheet next to it does not have.
• Damp material cuts much worse than dry. Stock stored in an unheated workshop over winter is a common culprit.
• It is not the material you think it is. Check that a “3 mm” sheet actually measures 3 mm.

More on this: how can I find the right parameters for my material?

6. Cooling and the laser source

Suspect the laser source only once steps 1 to 5 are ruled out.

Two patterns are worth separating:

• Gradual loss over a long period, evenly across the bed, with clean optics and correct focus. This is consistent with a laser source reaching the end of its life.
• Strong for the first 15 to 20 minutes, then progressively weaker. This is usually not the source. It points at cooling. Check the water temperature, the flow, and that the chiller is actually keeping up.

Start with the cooling side, because it is both cheaper and more likely: the water chiller in top condition.

Turning the power up is not a fix

If the machine needs more power than it used to for the same job, something on this list is wrong. Running at a higher current to compensate shortens the life of the laser source and hides the real fault until it gets worse.

On a BRM machine

The steps above link to the right article as you reach them. To jump straight to yours:

• BRM Original: air pump, laser head at 90°, the guides
• BRM Slim: air pump
• BRM Budget: air pump
• BRM Pro: air supply, laser head perpendicular
• Open Bed: alignment works differently, see mirror alignment for Open Bed machines

Still not cutting?

If you have worked through all six steps, written down what you changed and what it did, and the machine still will not cut through, get in touch. Send us:

• The material, its thickness, and the speed and power you are using.
• Whether the problem is even across the bed or worse in one area.
• What you have already checked from the list above.

That last point saves a great deal of time on both sides.