Why Is My CO2 Laser Not Cutting?

Applies to: MIRA and NOVA

This guide helps you work out why your laser will not cut through a material it should be able to cut. There are many possible causes: the material itself, such as a glue in an MDF composite that does not laser well, settings that do not suit the material, or a mechanical problem such as a failed component.

The checks below run from the most common cause to the least common across our customers. Unless a section says otherwise, there is no fixed order. Use your best judgment.

Settings

For thick materials (1/4” and above), 60 to 90% power at 5 to 20 mm/s is usually in the right range. For thinner materials (about 1/8” and below), start more conservatively, at 30 to 60% power and around 10 to 30 mm/s.

Speed and power depend on the wattage of the tube in your machine, not on its size. A NOVA 14 and a MIRA 9 have very different work areas, but with a 100 W tube in each they will likely cut with the same general settings.

Changing either speed or power changes the cut. Generally the speed needs lowering or the power needs raising. Change one variable at a time, for example lower the speed and keep the power constant, so you can see what fixed the problem. Lowering the speed alone makes the beam go deeper at the same power, because the laser stays on the same area for longer.

Check the Min and Max power settings in LightBurn too. Over short distances the laser may never reach the speed that triggers the Max Power setting, so the whole job is cut at Min Power. For cutting, we recommend setting Min Power to match Max Power.

Finally, make sure the unit and grid setting in LightBurn is not “inches / sec”. We recommend “mm / sec”. If you want your grid in inches, use “inches / mm/sec”, which shows dimensions in inches but keeps speed in mm. Most settings shared by other users assume speeds in mm/s.

Optic health

Clean mirrors and a clean focal lens are essential. The mirror on the laser head is especially exposed, because smoke often enters the laser head from above and the vapor bakes onto the mirror over time. Check both the laser head mirror and the focal lens regularly.

Smudges, soot and scratches all lower the output of the machine, because the dirty or damaged optic absorbs energy instead of passing it on. Even a small scratch at the center of a mirror or lens can cut the power leaving the nozzle by 20 to 40%, for each damaged optic the beam meets.

• Check the optics in the laser head after about 40 hours of use. Blow off large debris with compressed air and wipe clean with a lens wipe or a comparable optics cleaner.
• Check Mirrors 1 and 2 at the same time. Mirrors outside the active workspace get dirty or damaged much less often.
• Frequent dirt on the top mirror or focal lens can mean that your fume extraction is not sufficient, or that you are using too much air pressure.
• Debris on the underside of the focal lens can mean contaminated or insufficient airflow from the internal air pump or from an external air compressor.

For how to check and clean your optics, see the maintenance guides.

Make sure the focal lens is in the correct position in its cartridge and the right way up, with the convex (domed) side facing up:

• MIRA: the standard 2” lens and the optional 4” lens go at the top of the lens cartridge. The optional 1.5” lens goes at the bottom.
• NOVA: the 2.5” lens goes in the sliding housing. The 4” lens goes in the small red housing near the top of the laser head assembly.

See the lens guides for installing an alternative lens.

Laser head squareness

If you recently had a collision with the laser head, or bent the auto focus pin, see Squaring the Laser Head: MIRA and Replacing the Auto Focus Pin. When the laser head is out of square, the beam does not exit the nozzle properly and will likely clip the edge of the opening. That can mean a total loss of output power.

Alignment

A laser that is not aligned properly will never perform as it should. The beam must travel unobstructed across the whole series of mirrors, through the laser head and out of the nozzle. Check the alignment after checking the optics or adjusting squareness.

Before you make any adjustment, check the alignment and photograph each burn mark on a new piece of tape. If something is clearly off, run through the alignment process:

• MIRA Pro alignment videos
• NOVA alignment video

If the laser is perfectly aligned and still fails to cut, examine the beam path as it leaves the nozzle. Power is most often lost inside the laser head: when the beam path is wrong, the focused beam does not fully exit the nozzle.

1. Bring the laser into focus on the material.

2. Run a 1” square test cut with conservative settings.

3. If it does not cut through in one pass, remove the nozzle from the laser head and repeat the test next to the first one.

4. If it cuts through with the nozzle removed, the beam was clipping the inside of the nozzle and the beam path needs adjusting. Follow 5 Point Test: MIRA or 5 Point Test: NOVA.

Focus

This step is often overlooked. Jog the laser head so the auto focus pin, or the nozzle on a modern NOVA, is over your material, then run the auto focus command from the keypad.

On a MIRA, the auto focus pin can come loose and give the wrong focal distance. A loose nozzle does the same when you auto focus a NOVA or focus manually. Make sure both the nozzle and the auto focus pin are screwed in all the way, then auto focus on the material. Confirm the focal distance by measuring from the nozzle to the surface of the material with a focus gauge. It should be within 0.5 mm of the standard manual focus depth.

There are uses for running out of focus, but cutting is not one of them. Always be in focus when you cut.

Air flow

Enough air leaving the nozzle matters in every cutting job. It keeps smoke out of the path of the beam, helps keep the optics clean and puts out small flare-ups quickly. Too little airflow can mean cuts that do not pass through the material, a clogged nozzle, a melted airline or a fire inside your machine.

With the bed all the way down, examine the opening of the nozzle and the underside of the laser head bracket for charring. Check that the airline is intact and properly connected to the air fitting on the laser head. If you find damage or feel an air leak there, contact support.

If everything looks right, power the machine on and hold a piece of paper under the nozzle, to confirm that air is leaving the nozzle and is free of moisture.

Chiller water

Contaminated water can cause a loss of power at the laser tube itself. You may notice it during an alignment, when a pulse leaves a ring-shaped burn instead of a solid circle. Algae and dissolved solids from the piping of the chiller and machine contaminate the water over time. The water then absorbs energy sent to the tube, instead of letting it leave the tube as a strong beam.

We recommend changing the chiller water every 3 months. If it has been longer, flush the system:

1. Empty the water from the chiller into a bucket.

2. Refill the chiller with distilled water and power the machine on to cycle the system for a moment.

3. Power the machine off and empty the chiller again.

4. Fill and empty the chiller 3 to 5 times in total, then try cutting again.

Contaminated water causes four main problems:

• Heat dissipation. A CO2 laser tube produces a lot of heat, which the chiller carries away. Dirty water acts as an insulator, so less heat leaves the tube. The tube can overheat, perform poorly or be damaged.
• Tube contamination. Dissolved solids and minerals deposit on the inner walls of the tube over time. The buildup affects beam quality and efficiency.
• Corrosion and erosion. Corrosive substances in the water can corrode the internal components of the tube and weaken it. Impurities can also erode its internal surfaces.
• Optical distortion. Contaminated water can distort the beam, which affects its quality and precision.

For chiller maintenance, see Recommended Maintenance: MIRA or Recommended Maintenance: NOVA.

Material

The material itself can be the problem. Not all materials suit laser cutting. Commonly cut materials include acrylic, wood, paper, cardboard, fabric and leather. CO2 lasers are not designed to cut metal.

• Warping. Material can arrive warped, or warp in storage. Warped material is not level or in focus across the bed, and may not cut. Before a cut job, check the focus at all 4 corners and the center of the material. Some materials also warp or deform from the heat of the cut.
• Reflective materials. Metal and other reflective materials can reflect the beam and damage the optics or the laser tube. For cutting or marking metal, a fiber laser is the right tool.
• Surface finish. Smooth, flat surfaces generally cut more cleanly. Rough or textured surfaces may need different settings, such as a changed focal length, or masking tape to protect the surface.
• Color. CO2 lasers work at a wavelength of about 10.6 micrometers, which darker materials absorb most effectively. Lighter materials reflect more of the energy, so they may need more power or cut less efficiently.

Fume extraction

Clearing smoke from the cabinet quickly is key when cutting. A telltale sign that your extraction needs work is seeing the red beam entering the laser head for long periods during a job, most visibly towards the front of the machine. Smoke and debris around the cut obstruct the beam, which leads to poor cut quality, incomplete cuts or uneven cutting depth.

If lingering smoke has become steadily worse, you may just need to clean the exhaust fan. See the exhaust cleaning steps in Recommended Maintenance: MIRA or Recommended Maintenance: NOVA. If the problem has been there since day one, review your whole ducting system.

• Keep the exhaust run as short as possible.
• Avoid 90 degree turns and keep the number of bends to a minimum.
• If the exhaust run is longer than 15 ft, add an inline fan towards the end of the run.
• Do not reduce the ducting below the diameter of the supplied exhaust hose (6”).
• Use as little of the supplied exhaust hose as possible to reach the nearest wall. A little slack is fine.
• Avoid a cap or vent at the end of the run. A blast gate that opens and closes fully is ideal.
• Consult an HVAC professional for your setup whenever possible.

Machine components

Last, check that the laser tube and the laser power supply are in good condition. As a laser tube nears the end of its life it gradually loses power, and you may have seen the pulse marks weaken during the alignment check. A completely dead tube may arc from the high voltage cable whenever it is pulsed, with a clicking sound.

1. If the machine was running recently, leave it off and unplugged for a few minutes first.

2. With the machine off and unplugged, open the laser tube compartment. Inspect the glass for cracks, particularly at the core where the water flows. Check that no water has leaked into the outer core of the tube, and that there is no algae or discoloration in the inner tube or its water lines. Inspect the two wires that connect to the tube for burns or melting.

3. Remove the left access panel, as seen from the front of the machine. Inspect the red high voltage wire and the area around the laser power supply for signs of burning.

4. If all is well, close the laser tube compartment and plug the machine back in. Power it on, leaving the left access panel open. Check that the red LED readout on the laser power supply is lit while the machine sits idle.

5. Run a job as you normally would and watch the red LED readout. It should show a series of numbers and letters during operation. Note what it shows, and contact support@aeonlaser.us if needed.