How to Clean Focal Lenses and Laser Mirrors for CO2 Laser Engraver Machine

Have you ever tried watching TV through dirty glasses? If so, you know how the image can get distorted, and how cleaning them brings back that crystal-clear view.

The same principle applies to your laser cutter, which uses mirrors and lenses to reflect and focus the laser beam onto your workpiece. Just like the TV, dirty optics can lead to poor performance, but with a laser, the stakes are higher because the beam is hot and powerful.

When you use your laser engraver to cut various materials, the process vaporises the material, releasing airborne particles, smoke, and gases. These contaminants can settle on your mirrors and lenses. If you fire up the laser again without cleaning, these particles can burn onto the surface, causing permanent damage.

A clean mirror reflects the laser beam energy efficiently along a single path. But if there's debris, the beam can scatter, reducing its power and affecting the quality of your cuts and engravings. Additionally, a dirty mirror can absorb infrared energy, leading to overheating and potential cracks in the optics.

In summary, keeping your laser mirrors and lenses spotless is crucial for optimal performance and longevity of your laser cutter. Regular cleaning ensures that you get the best results from your equipment.

What Causes Dirty Laser Mirrors and Focal Lenses?

When cutting materials like wood or acrylic, the laser vaporises the material beneath it, producing smoke that ideally gets extracted through the ventilation fan. However, even with effective ventilation, some smoke will still circulate around the laser machine, causing particles to settle on various surfaces, including the mirrors and lenses.

During engraving, not only is material vaporised, but some is also burnt or charred, creating even more smoke and worsening the contamination issue.

 As the laser operates, air is directed through the nozzle, creating positive pressure that pushes air—and ideally debris—out alongside the laser beam. This airflow is meant to prevent particles from the cut area from entering the nozzle. However over time, some smoke and debris can still be drawn back in, contaminating the underside of the lens.

Additionally, if you use tape while aligning the mirrors or laser head, it can lead to residues on the mirrors or smoke marks on the lens surface.

Regular cleaning of the mirrors and lenses is crucial. Keeping your workspace tidy and reducing excess dust in the area is equally important. We recommend performing a simple clean-in-place procedure at the end of each job and conducting a more thorough clean weekly.

Laser Engraver Maintenance: Cleaning Laser Mirrors

What Should I Use to Clean My CO2 Laser Mirrors?

To clean your CO2 laser mirrors, use single-use lens cleaning paper tissues soaked in isopropyl or denatured alcohol with a concentration of 90% or higher. Alternatively, a clean, lint-free microfiber cloth can work, but ensure it is spotless. Avoid using cheaper cleaning solutions, as they may leave residues. Never use cleaners containing ammonia on your laser mirrors or focus lenses.

How to Clean Laser Mirrors

At the end of each job, and with the laser switched OFF, wipe down each of the three mirrors using wet lens cleaning wipes, which are available in convenient individual packets for cleaning reading glasses.

Access the Mirrors: Open the access doors to ensure you can easily reach each mirror, then take out a wipe.

Clean Mirror 1: Fold the wipe in half and gently wipe Mirror 1 (the one at the end of the laser tube).

Clean Mirror 2: Fold the wipe in half again and use it to clean Mirror 2. The surfaces should dry within a few seconds, and you can use a flashlight to check for cleanliness. You might notice yellow staining on the wipe—that’s the smoke residue from cutting and engraving.

Clean Mirror 3: Cleaning Mirror 3 is a bit trickier as it’s located inside the laser head. Wrap the folded wipe around a Q-tip and use it to clean Mirror 3. Typically, this mirror is less contaminated, likely because it’s more enclosed.

Wait Before Using the Laser: Avoid operating the laser for at least 15 minutes after cleaning to allow any moisture to fully evaporate.

Cleaning Mirrors: Weekly Maintenance

At the end of each week, along with cleaning and lubricating the linear bearings and axis slides, we perform a thorough cleaning of the mirrors and lens.

To do this, make sure you have good access to the mirrors through the access doors and remember to switch the laser OFF while cleaning. It’s also a good idea to wear clean cotton or latex gloves to avoid leaving fingerprints and to protect your skin.

Tools Needed:

You will need a mirror removal tool. If you don’t have one, you can use a pair of circlip pliers carefully.

Removing the Mirrors:

The mirror is secured by a threaded ring that can be unscrewed. Insert the tool or the tips of the pliers into the two holes on the back of the mirror mount and turn counterclockwise. Be careful not to apply too much pressure, as this could disrupt the mirror alignment, which is crucial for the laser cutter’s performance.

Once the retaining ring is unscrewed, use a piece of masking tape to gently lift the mirror from its holder. This method can be used for all three mirrors to prepare them for deep cleaning.

Cleaning the Mirrors:

Instead of using wipes, clean the mirrors with a specially designed lens cloth soaked in 100% isopropyl alcohol. Avoid using cheaper cleaning solutions, as they can leave residues, and never use cleaners that contain ammonia on your laser mirrors or focus lenses.

Wipe each mirror firmly to ensure all contamination is removed, then inspect the surface closely. If you notice any pitting or damage, the mirror should be replaced, as they cannot be repaired and are considered consumable items. It’s wise to keep one or two spare sets on hand.

Reinstalling the Mirrors:

Once all three mirrors have been cleaned and allowed to dry, replace them in their holders and tighten the retaining rings. DO NOT OVERTIGHTEN—they only need to be tight enough to prevent the mirror from moving. Over-tightening can cause the mirror to break or become distorted.

The mirrors can be reinstalled in any order, as all three are identical.

How to Clean the Laser Focus Lens

We recommend cleaning the laser focus lens during weekly maintenance or whenever you notice a decline in cutting performance. This can happen after extended engraving jobs or if the air assist is not turned on.

Identifying Your Laser Head Type:

There are various types of laser heads. Some have the lens located in the nozzle, while others feature a lens tube secured in the head by a single screw. You can identify which type you have by first removing the nozzle. Loosening the screw will allow you to take out the lens tube. If necessary, lower the bed of the laser cutter to facilitate removal. If your lens is inside the nozzle, simply removing it from the head will give you access to the retaining ring.

Removing the Lens:

Once you’ve removed the lens tube, the lens itself is held in place by a threaded retaining ring similar to that of the mirrors, but it’s deeper inside the tube. You’ll need a removal tool, or long circlip pliers may help you unscrew the ring. Under the ring, you should find a silicone O-ring and then the lens itself.

Carefully invert the lens tube to remove the O-ring and lens. Handle the lens with caution, as its special coatings are prone to scratching.

Cleaning the Lens:

Clean the lens just like the mirrors, using a lens cloth and pure isopropyl alcohol. Make sure the lens is spotless and free of scratches. Damaged lenses should be discarded and replaced, as they are consumable items. Always keep a spare lens of the same focal length and diameter on hand.

Reinstalling the Lens:

When replacing the lens, gently drop it back into the tube with the ‘convex’ side facing down first, followed by the O-ring and then the threaded ring. Tighten the threaded ring to ‘finger tight’ only—this is just to ensure the lens stays in place.

When reinserting the lens tube into the head, make sure the convex side is facing upwards. Remember: ‘belly up’ to help you assemble it correctly!

How to Clean the Laser Tube Lens

There’s one more lens that requires attention, though you’ll likely only need to clean it every few months or if you experience performance issues that mirror and focus lens cleaning doesn’t resolve. At the firing end of the laser tube, there’s a small lens that sits deep inside the tube. This lens can only be inspected using a mirror. While it doesn’t typically get contaminated, smoke buildup in the laser tube chamber—especially if the ventilation fan fails—can lead to contamination. Therefore, we recommend cleaning this lens every few months as a precaution.

Cleaning Your Laser Tube Lens: Step-by-Step Instructions

 Turn Off the Laser: Ensure your laser machine is switched OFF.

Prepare the Q-tip: Bend a Q-tip to a 90-degree angle to help you reach the lens inside the laser tube.

Dip the Q-tip: Lightly dip one end of the Q-tip into 100% isopropyl alcohol.

Clean the Lens: Gently insert the wet end of the Q-tip into the laser tube and wipe the lens in a circular motion a few times.

Avoid Acetone: Do NOT use acetone, as the end of some laser tubes is glued during manufacturing, and acetone can damage the glue. After cleaning, avoid operating the laser for at least 15 minutes to ensure the lens is completely dry.

Conclusion: Cleaning Your Laser Mirrors & Focus Lens

To maintain your laser cutter’s optimum performance, various systems must work in harmony. The laser beam must be generated correctly in the tube, reflecting off three perfectly clean mirrors before passing through a spotless focus lens. If any part of the optics system is compromised, the laser will not operate at 100% efficiency.

Keeping mirrors and lenses clean not only affects beam quality but also prevents rapid component failure, which can lead to costly replacements and downtime.

Always perform a quick cleaning procedure with pre-moistened lens wipes at least once every day you use your laser. Additionally, include a deep clean and inspection as part of your regular maintenance schedule. These preventive steps will extend the lifespan of your laser mirrors and focus lens, ensuring your laser is always ready to perform at its best.