Laser Engraver Mirror Alignment: How to Align a CO₂ Laser Beam

CO₂ Laser Beam Alignment: How to Align a Laser Engraver

The most intimidating task for many new CO₂ laser engraver owners is laser beam mirror alignment. Learning how to align the laser mirrors that direct the laser beam from the laser tube to the laser focusing lens and the workpiece is not always easy. However, you don’t need to fear the task, as this guide will walk you through how to align a CO₂ laser beam step by step while also pointing out some potential issues you might run into.

After you review the OMTech manual, prepare your workspace, and set up your laser machine, you will need to check your laser beam path alignment. Laser engraver mirror alignment is not as hard as you might think. Plus, once you get your CO₂ laser beam alignment correct, your laser machine will be engraving and cutting at peak performance, and you should rarely have to align your laser mirrors in the future.

The Basics: Laser Mirrors and the Laser Beam Path

Before we get into laser mirror alignment, we need to understand how a laser engraving machine works. While the picture below does not show your exact laser machine, it illustrates how the laser beam bounces off the laser mirrors.

The laser machine works by generating a laser beam from a CO2 laser tube located at the rear of the machine. This laser beam exits the tube and hits mirror 1 (located near the output of the laser tube in the rear of the laser machine). Mirror 1 bounces the beam at roughly 90 degrees toward the front of the machine.  

Here, the laser beam hits mirror 2. Note that mirror two is mounted to a gantry and therefore can move forwards and backward in the machine but cannot move left or right. Mirror 2 also bounces the beam at roughly 90 degrees but bounces it toward the right side of the machine.

At this point, the laser beam hits mirror 3. Note that mirror three is mounted to the laser head assembly, which is also on a gantry. That means this mirror can move left, right, forward, and backward. Mirror 3 bounces the laser beam at roughly 90 degrees down into the laser head, where it passes through a laser focusing lens (or focal lens), exits the laser head nozzle, and hits the workpiece.

All of these moving parts create the need for periodic adjustment. As your CO₂ laser engraves various projects, the laser mirrors can shift and move slightly over time. Each OMTech laser is aligned at the factory according to strict Quality Assurance practices, but the machine is typically jostled and shifted in its crate throughout the shipping process, which sometimes affects the laser beam alignment. Before you begin using your new OMTech for laser cutting and engraving, you’ll want to check to ensure your CO₂ laser mirror alignment is acceptable, and adjust the laser mirrors if necessary.

Accuracy vs. Precision

Next, before we go through how to align laser engraver mirrors, we need to understand the difference between accuracy and precision. Here are simple definitions of the two terms:

1. accuracy: the quality or state of being correct; hitting the intended target
2. precision:  the quality, condition, or fact of being exact; the ability to repeatedly produce the same result

A somewhat famous way to visualize accuracy and precision is in a bullseye target:

To summarize the difference:

• Accuracy is hitting the intended target (think bullseye). For the case of laser engraver mirror alignment, accuracy means hitting the dead center of the mirror.
• Precision is repeating the same thing multiple times (the dot is in the same spot over and over again). For the case of laser engraver mirror alignment, precision means hitting the same spot on the mirror regardless of where the gantry or laser head is located within the laser machine.

For mirrors 1 and 2, precision (the dot hitting the same place on the mirror every time) is much more important than accuracy (the dot hitting the center of the mirror).  This is true because the dot hitting the same place shows that the laser beam is parallel to the axis in the direction it is traveling. However, for mirror three, we need both precision and accuracy, as the laser beam must travel through the focusing lens and laser head nozzle.

How to Align Laser Engraver Mirrors

This CO₂ Laser Engraver Mirror Alignment Guide is intended to complement the instructions in section 5 of the OMTech Manual. See ‘Laser Path Alignment.’

How do laser engravers align mirrors?

Now that we have a basic understanding of what we are trying to align and what purpose it serves, we can move on to the actual instructions: how to align a CO₂ laser beam. Most laser engravers use the pulse-tape method to align laser mirrors (OMTech recommends using blue painter’s tape). By this method of laser beam alignment, you will place tape over the mirror guide holes and pulse the laser beam to determine where it hits each mirror (by observing burn marks on the tape). When necessary, you can make minor adjustments to the laser beam mirror alignment by turning the set screws that control the laser mirrors’ position.

NOTE:  If your laser machine came with the laser tube installed, there is a good chance that your laser mirrors are already aligned and may not require any adjustment. Before loosening any nuts or adjusting any mirrors, first do the pulse test outlined below to see if an adjustment is necessary.

How do you align a CO₂ laser?

The laser beam from the laser tube to mirror one rarely requires adjustment.  Because the laser tube itself and the mirror one mount are stationary, there is no movement between them when the machine is operating. In a future step (aligning the laser beam from mirror 2 to mirror 3), you may have to adjust the laser tube up or down, but for now, we start by verifying that the laser tube is pulsing to mirror 1.

Warning:  Be sure to wear proper eye protection when aligning the laser mirrors.  Never bypass the machine’s safety features or operate the laser with the lid or access panels open.

Step 1: Optimize Your Pulse Setting

Pulse Settings: In your controller, you want to change the pulse setting to a power level that provides a good consistent pulse but without using too much power that could catch the tape on fire. To do this, follow these steps:

1. On your controller, open the menu by pressing the “menu” button

2. Move the highlighted area to the “MaxPower” setting and press “Enter”. Change the MaxPower to the appropriate power level. I suggest starting around 5% and then increasing 1% at a time until the pulse produces a mark on the tape.
3. Press “Enter” to save the changes.
4. Move the highlighted area to the “MinPower” setting and change it to match the MaxPower setting.
5. Ensure your water cooling system is on and running before performing any pulses.
6. It is helpful to have a friend push the pulse button while you monitor where the pulse hits the tape each time.

LASER FIRE HAZARD: Before pulsing, ensure you have the proper fire protection in place. If you pulse with too much power, the tape can catch fire.

Step 2: CO₂ Laser Tube Alignment: How to Align the Laser Tube

Laser Tube to Mirror 1 Pulse Test: Laser tube alignment is necessary to ensure that the laser tube is pulsing correctly and hitting mirror 1.

1. Place a small piece of tape over the guide hole on mirror 1.
2. Press the pulse button on the controller. NOTE: The longer you hold the pulse button, the longer the laser tube beam will stay on. You want to push the pulse button just long enough to produce a pulse but should not hold the button down. The controller should beep each time the pulse button is pushed.
3. Inspect the tape to ensure a mark was made when the pulse happened and that the mark is within the circle of the guide hole. The tape's pulse mark indicates where the laser beam would hit mirror 1. It should look something like this:
4. If there is no mark on the tape, it is most likely due to the pulse power being too low or pushing the pulse button too quickly.  
1. Try adjusting the min and max power by increasing 1% and then pulsing again. NOTE: Each laser tube has a minimum power at which it will fire. Our 60W tube won’t fire below around 8% power while our 130W tube won’t fire below around 12% power.
2. Repeat as necessary until the tape shows a laser beam mark.
5. If the burn mark on the tape is too large or the tape burned:
1. Double up or triple up the tape (put one piece of tape on top of another piece of tape) to keep it from burning through.  
2. Try a different type of tape. If your laser came with the white roll of tape, this is a good alternative.
3. Try adjusting the min and max power, decreasing by 1%, and then pulsing again.
6. If the pulse dot was not within the guide hole, or it is near the edge of the guide hole circle, you will need to adjust the laser tube mounts to move the pulse dot within the guide hole and repeat the process.
7. Loosen the laser tube mounting brackets. Then, reposition the tube and pulse until it points to the center of laser mirror 1

REMEMBER: The dot does NOT need to be perfectly centered on the guide hole (accuracy); it just needs to be near the center of the guide hole, and each pulse should hit the same spot (precision).

Step 3: Align the First Laser Mirror

Mirror 1 to Mirror 2 Alignment: Remember that our goal is to get the laser beam parallel to our y-axis (the axis that runs from front to back of the machine).

1. Place a small piece of tape over the guide hole on mirror 2.

2. From the controller home screen, press the up arrow to jog the gantry all the way to the back of the machine.  This will move mirror 2 closest to mirror 1:
3. Press the pulse button on the controller.
4. Inspect the tape for a pulse mark. If there is no mark on the tape, it is most likely that mirror 1 is bouncing the laser beyond the tape area. To check for this, use a larger piece of tape in front of mirror two’s guide hole and pulse the laser to see where it hits. If the tape still doesn’t mark, you can attach a larger cardboard or cardstock paper to the mirror’s guide hole. Then move on to adjusting the mirrors below.
5. Once you have a pulse mark on the tape, note its location and then move the gantry to the front by jogging it (using the down arrow key on your controller).
6. Have a friend person push the pulse button while you watch where the laser beam pulse hits the tape.
1. Near Alignment VS. Far Alignment: If you are lucky and the 2nd pulse hits the same spot as the first pulse, you can move on to “Mirror 2 to Mirror 3 Alignment” below.
2. If the 2nd pulse did not hit the same spot as the 1st pulse, do not fret.  You will need to loosen the nut(s) on the appropriate screws on mirror 1 and adjust the screws in order to move mirror 1 until the laser beam hits the same spot on the tape. See the following image for which screw to turn and which direction to turn it.
3. REMEMBER: We are not worried about the dots hitting dead-center on the mirror (accuracy); instead, we want the two dots to hit the exact same spot when the gantry is moved (precision).

How to adjust a laser mirror

• Do not use the diagonal mirror screw adjustment unless the left/right or up/down screw can no longer adjust the dot in the correct direction.
• If you do end up using the diagonal screw adjustment, you can use it in combination with another screw to move the dot in a straight direction line up/down or left/right.
• You should make small adjustments to the screw before pulsing again and reviewing where the new pulse hits the tape. A good rule-of-thumb is no more than 1/8th turn before pulsing again to check. This is particularly true with laser machines that have a large engraving area as small-angle adjustments of the mirror cause the laser beam adjustment to become dramatic over longer distances.

1. Once you have the 2nd location laser beam pulse on the same dot as the 1st laser beam pulse, you should now replace the tape with a new piece of tape and REPEAT the procedure.
1. IMPORTANT NOTE: You MUST repeat the procedure because adjusting the screws changes the 1st pulse location as well as the 2nd pulse location. Note that this may take many repeated cycles to get the alignment to the point where the 2nd pulse location matches the 1st pulse location without adjustment. This is normal, and while it may seem time consuming, it is worth getting this right to ensure your laser is operating at peak performance across the entire workbed.
2. Once the 2nd pulse hits the same location as the 1st pulse WITHOUT adjusting any screws, you can now carefully tighten the retaining nuts and move on to “Mirror 2 to Mirror 3 Alignment”.
1. IMPORTANT NOTE:  It is critical that the screws do NOT turn when tightening the retaining nuts. Hold the alignment screws in place while tightening the nuts to ensure they do not move.
3. Remove the tape from mirror two's guide hole and dispose.

Step 4: Align the Second Laser Mirror

Mirror 2 to Mirror 3 Alignment: Our goal in this part is to get the laser beam from mirror 2 to mirror 3 to be parallel to the x-axis of the laser machine (the axis that is left and right in the machine).

1. Place a small piece of tape over the guide hole on mirror three on the laser head.

2. Move mirror 3 (the laser head) to the back left of the machine by jogging the gantry to the back left of the machine (press the up arrow and left arrow on the controller when on the home screen).
3. Press the pulse button on the controller.
4. Inspect the tape to ensure a mark was made when the pulse happened.  
1. If there is no mark on the tape, it is most likely that mirror 2 is bouncing the laser beyond the tape area.
1. To check for this, use a large piece of tape or cardboard in front of the mirror 3 guide hole and pulse the laser to see where it hits.  Then move on to adjusting the mirrors below. 
2. Ensure you removed the tape from the mirror two guide hole.
5. Once you have a good mark on the tape, note its location and then move the gantry to the back right by jogging it (using the right arrow key on your controller).
6. Have a friend push the pulse button while watching where the laser beam pulse hits the tape.
1. If you are lucky and the 2nd pulse hits the same spot as the first pulse, you can move to step 7.
2. If the 2nd pulse did not hit the same spot as the 1st pulse, you will need to loosen the nut(s) on the appropriate screws of mirror 2 and adjust the screws to adjust mirror two until the laser beam hits the same spot on mirror 3. See the following image for which screw to turn and which direction to turn it. Remember to avoid using the diagonal screw unless absolutely necessary.
7. Once you have the 2nd location laser beam pulse on the same dot as the 1st laser beam pulse, you should now replace the tape with new tape and REPEAT the procedure. IMPORTANT NOTE:  You MUST repeat the procedure because adjusting the screws changes the 1st pulse location and the 2nd pulse location.
8. Once the 2nd pulse hits the exact location as the 1st pulse WITHOUT adjusting any screws, you should replace the tape on the laser head with new tape and continue to the next step.
9. Move mirror 3 (the laser head) to the front left of the machine by jogging the gantry to the front left of the machine (press the down arrow and left arrow on the controller when on the home screen).
10. Press the pulse button on the controller.
11. Inspect the tape to ensure a mark was made when the pulse happened.  
1. If there is no mark on the tape, it is most likely that mirror two is bouncing the laser beyond the tape area.
1. To check for this, use a large piece of tape or cardboard in front of the mirror three guide hole and pulse the laser to see where it hits.  Then move on to adjusting the mirrors below. 
2. Ensure you removed the tape from the mirror 2 guide hole.
12. Once you have a good mark on the tape, note its location and then move the gantry to the front right by jogging it (using the right arrow key on your controller).
13. Have a friend push the pulse button while you watch where the laser beam pulse hits the tape.
1. Because we made the laser beam parallel to the y-axis in a previous step, the dot at the front right should hit the same spot as the dot from the front left.
2. If the 2nd pulse did not hit the same spot as the 1st pulse, there is a good chance your mirror alignment from mirror 1 to mirror 2 is not correct. Go back to that step and repeat it.
1. Another potential issue would be one of the gantries being out of square. While this is possible, it is not common. In these cases, it is best to contact OMTech for assistance.
14. For mirror 3, we need the dots to be both accurate (centered on the mirror) and precise (hitting the same spot on the mirror each time). To center the dots, follow this procedure:
1. Review your pulses and take the following actions if they are not centered on mirror 3.
1. To move the dot up or down, the entire laser tube should be raised or lowered. This is accomplished by loosening the cap screws in each mount and turning the thumbscrew.
1. NOTE: Ensure that both mounts are raised or lowered by the same amount.
2. Tighten the cap screws in each mount and then perform the pulse and ensure the dot is centered vertically in the mirror 3 guide hole.  
3. Repeat this process by moving the laser tube up or down until the dot is centered in the mirror 3 guide hole.
2. To move the dot left or right, the mirror 2 assembly mount must be moved forward or backward within the machine.
1. Loosen the 2 screws underneath the mirror 2 assembly just loose enough to where the mirror 2 assembly can be moved forward or backward. IMPORTANT NOTE: You need to try to keep the mirror 2 assembly square when moving it.
2. To move the dot to the right, the mirror two assembly must move forward (toward the front of the machine). To move the dot to the left, the mirror two assembly must move backward (toward the rear of the machine).
3. Tighten the screws and perform a pulse test to ensure the beam is now centered horizontally on the mirror three guide hole.
15. Once this process is completed, you need to repeat the process for “Mirror 2 to Mirror 3 Alignment” detailed above.

Step 5: Laser Alignment: The Third Laser Mirror

Mirror 3 to Bed Alignment: In this step, we ensure that mirror 3 is bouncing the laser beam through the center of the focusing lens and nozzle.

1. Start by ensuring the tape has been removed from all laser mirror guide holes.
2. Place a scrap piece of material (wood works best) under the laser head nozzle.
3. Adjust the bed height such that the laser head nozzle is nearly touching the scrap piece of material.
4. Perform a pulse by pressing the pulse button on the controller.
5. Ensure the pulse marked the material.
1. If a double pulse or crescent shaped mark appears, that means the laser beam is hitting the inside of the laser head nozzle before exiting.
1. In this case, adjust the screws on mirror three and pulse until a singular small dot is visible on the material.
2. If no mark is present, it’s possible that mirror 3 is very misaligned. Take the nozzle off and check the alignment — without the nozzle you have a larger area for the beam to reveal itself. Once you see the beam path without the nozzle you can center it as best you can before screwing the nozzle back on. After it's centered without the nozzle, screw it back on, recheck your alignment, and fine tune it from there.
3. As a last resort, I suggest unscrewing all 3 screws until they no longer affect mirror three alignment and then repeating the pulse.
6. Move the bed at least 1 inch further away from the laser head nozzle.
7. Perform a pulse by pressing the pulse button on the controller.
1. If the 2nd pulse did not hit the same spot as the 1st pulse, you will need to loosen the nut(s) on the appropriate screws of mirror three and adjust the screws in order to adjust mirror three until the laser beam hits the same spot on the material. See the following image for which screw to turn and which direction to turn it.
   REMEMBER: Avoid using the diagonal screw unless absolutely necessary.
8. Move the bed at least 1 inch further away from the laser head nozzle and repeat the pulse test and mirror three alignment.
9. If you adjusted any mirrors, you need to repeat this process until all three dots hit the same spot without adjusting any mirrors.

Conclusion

In this article, we taught you how to align laser engraver mirrors with step-by-step instructions. While this process can be time-consuming and sometimes frustrating, remember that taking the time to get this right will set you up for future success with your laser machine. If you feel frustrated, take a break and walk away from the machine for a while. You can do this, and it does get easier each time you do it!

Once you have your laser beam alignment done, you can learn how to laser engrave on various materials, like wood, glass, or even stone.

Author Bio:

Patrick S.  

When the COVID-19 pandemic hit in early 2020, my kids (9, 7, and 4 at that time) and I found we had a ton of extra time on our hands.  Instead of spending this time on screens, I decided we should learn a new skill. While I've always done some woodworking mainly for our own use, we purchased a small CNC diode laser and learned how to use that. We gave away many items and eventually had requests for custom items, so we started asking them to pay. From this, our "accidental side business" was born. We ended up purchasing an OMTech laser to aid in our ability to engrave and cut wood at speed. Today, we have a CNC wood router, a small diode laser, an OMTech 60W 20" x 28" laser machine, and an OMTech 130W 35” x 55” laser machine.