Lasers 101:

How CO₂ Lasers Cut Acrylic

The reference page for how a CO₂ lasers works. A little understanding can help a lot when something goes wrong.

Every troubleshooting question on this site links back to this article. Common laser questions about melting, warping, rough edges, partial cuts trace back to a handful of things:

  1. how well your laser is set up, and

  2. the laser power, speed, and airflow settings.

This is the one page that explains it all in full. This way the troubleshooting articles can stay focused on your specific problem instead of re-teaching the basics every time.

Jump to a section, or read straight through if you're building real working knowledge of your machine.

Laser Types

CO2 Lasers

An industrial cutter designed for continuous operation. CO₂'s strength is cutting and engraving organic and non-reflective materials like:

  • Leather

  • Fabric

  • Cork

  • Wood

  • Plastics

  • Paper

CO₂ will cut metal, but with caveats:

  • Has to be thin, mild or stainless steel.

  • Will not cut shiny metals like copper, aluminum or gold. The beam bounces off instead of being absorbed. This can damage your optics if you are not careful.

These lasers are great at detailed engraving work and cutting thin materials with precision rather than speed and throughput

Diode Lasers

A compact, low cost laser built around the semi-conductor industry. The same technology as a laser pointer and barcode reader. Diode lasers work best engraving dark, non-reflective materials like:

  • Wood

  • Anodized Metal

  • Dark or opaque acrylic

  • Leather

Diode lasers will cut some materials, but not all:

  • Works best on wood, dark acrylic and leather.

  • Will not cut clear, light colors, or mirrored acrylic.

These lasers are built for affordability and their compact size. The are great at engraving but limited at cutting when compared to CO₂.

Fiber Lasers

High power and high precision. Fiber lasers were designed to send kilowatts of power down a fiberoptic tube for the purpose of cutting metal. Fiber lasers great at engraving and cutting metals like:

  • Stainless Steel

  • Aluminum

  • Brass

  • Copper

  • Titanium

  • Gold

Fiber lasers limitations:

  • Will not cut wood, leather and most plastics. They tend to burn rather than cut.

  • Will not cut clear, light colors, or mirrored acrylic.

2 types of lasers available:

  • Desktop Engraving: 20-100W

  • Industrial Cutting: 1 - 30kW+

If you are looking to engrave or cut metal, fiber lasers are the correct choice.

The Variables That Control a Laser Cutter

Every cut you've ever made comes down to four things:

  1. Power - The amount of energy generated by the laser tube

  2. Optics - How much of that energy reaches the material and how concentrated is the beam

  3. Speed - The length of time the energy stays in one place

  4. Air-Assist - Clears the heat, vapor and debris from the cut

All four sections are really about one thing… managing heat.

Power generates the heat. Optics delivers and focuses the heat. The speed controls how long the heat stays in one place and the air assist clears heat and debris away.

Learning about these four variables can help you diagnose almost any acrylic problem without guessing.

Power

Power is the term used to describe how much energy the laser is producing and applying to the material at any given point. These settings are usually set inside the cutting and engraving program when you are designing the job. In most cases, you can also adjust the power settings at the machine for fine tuning or adjusting based on the material you are using.

  • Too little power and the beam can't fully vaporize the material

  • Too much power and the heat will spread into the material you didn't want to touch

Make sure to check and follow the laser manufacturers recommendations for power limitations. Most laser tubes will last thousands of hours before losing power and needing replacement. Going above and beyond the max rated safe operational power will reduce the laser tube life.

Getting it right

  • Start with known good settings and test on some scrap. Never guess at the settings with a new or production piece

  • Make adjustments in small increments and record every change

Troubleshooting

Won't cut → power too low, not enough energy to get through the sheet

Rough edges → too little power tears instead of cutting clean; too much melts and rounds the edge over

Melting → too much power (paired with too little speed) is one of the two main causes

Warping → too much power puts more heat into the sheet than it can shed

Engraving too deep → power too high is the primary driver, check before touching focus/resolution

Fire → too much power (or too slow a speed) lets heat build faster than it can dissipate, increasing flare-up risk

Optics

Mirrors and lenses deliver the beam from the laser tube to the material. They need to be clean, aligned properly and made from a suitable material that can reflect the laser beam properly. Dirty lenses and mirrors scatter and absorb energy before it ever reaches the acrylic. So "weak laser" complaints are often an optics problem, not a tube problem. The lens focuses the beam to its smallest, sharpest point at one specific distance. Adjust the lens up or down to get the focal point of the laser beam into the middle of the material.

the main symptoms of an optics problem are:

  • Wider cuts

  • Rougher edges

  • Weaker cuts

  • Blurry engraving

Not all mirrors and lenses are made equally. Before replacing anything, check the laser tube manufacturers data sheets and ensure that you are purchasing something that is rated for the output of the laser.

Maintenance

  • Clean the mirrors and lenses regularly. This is the easiest and most common fix for a “weak beam” problem

  • Check the alignment periodically. The laser motors will make everything vibrate and shift over time.

  • Not all lenses are ground evenly… I use a piece of spaghetti to see how far out the nozzle the beam should focus, and then a mm step gauge to really dial in the focus.

Troubleshooting

Losing power → clean the lens and mirrors, then check the alignment

Rough edges → dirty or a misaligned lens. check to see that the lens is secured properly and mirror 3 is properly aligned

Fire → smoke and soot buildup on mirrors and lens reduces efficiency. A weaker beam needs more power to do the same work, which raises the risk of fires

Uneven cutting → run the same test in a few different spots on the laser bed. If the weak spot stays in the same place on the bed no matter what sheet you use, it's the optics. If the weak spot moves with the sheet, its the material

Out of focus → Is it a dirty lens or a z-height problem? Clean the lens and then doublecheck that you have the correct lens installed and that is is the correct distance from the material

Speed

Laser speed of the laser determines how long the beam stays in one place.

  • Too fast and it doesn’t spend enough time to full cut the material

  • Too Slow and the beam will overheat the cut around the line

A general rule is that the faster your laser moves, the more power it will need to cut and engrave.

Getting it right

  • Same as the power, test on scraps while making small incremental changes. You will find yourself making changes to the speed and power at the same time.

  • If you're not sure whether to adjust the power or speed first, bump speed up 10–15% before touching power. Most melting and heat issues resolve there first.

Troubleshooting

Won't cut → too fast will leave a scored line instead of a cut line

Rough edges → fast speeds will leave a jagged and incomplete edge. slow speed will lead to wider kerf

Melting → too slow for the amount of power applied to the material 2is one of the two primary causes

Warping → too slow a speed puts more heat into the sheet than it can shed and as a result it will start to warp before melting

Engraving too deep → the speed is too slow and the power may be too high.

Fire → cutting too slowly gives heat more time to build and ignite vapors

Air Assist

An air pump blows hot gases, smoke, and melted debris out of the cut path before they can re-deposit, re-melt, or ignite. It's doing double duty: clearing the cut line and managing heat. Cutting thicker material requires more are than thinner material and engraving requires none.

Before loading material into your laser bed, check your air source to make sure you have adequate airflow. A lot of the soot, burning, dull and haziness is a result of poor airflow.

Getting it right

  • Confirm the compressor is producing strong, consistent airflow

  • Check for a blocked nozzle or a kinked line. A weak flow at the nozzle can come from either

Troubleshooting

  • Fire → poor air assist is the most common cause of a flames and flare ups. it happens when small pieces fall through the bed and allows for the smoke and vapors to contact the laser beam

  • Melting → The air clears hot gas and debris before they heat and distort the surrounding material. make sure there is enough flow to do the job.

  • Soot/smoke on the acrylic → poor air assist and exhaust is not clearing the smoke fast enough. The soot collection tells you whether it's an airflow or a cutting problem

  • Dull/hazy engraving → We will us the air assist for all cutting and some engraving. For deeper engravings that are going to be painted, we will us a little air to prevent fouling the lens. We do not use any air assist for engraving 2 toned plastics.