[Laser.Tech]

Laser.Tech's Guide To Aligning CO2 Beam Delivery Optics

Aligning a high power laser thru it's delivery optics is a basic step that is ESSENTIAL for getting the most accurate work results and preventing damage to the equipment, and most importantly keeping it SAFE to use!

The basic principle is quite simple. Put some type of material (i.e. index card) in front of the beam. Turn the beam on long enough to discolor the material. This indicates the location of the beam. Adjust the beam direction until the position of the beam is where you want it. Repeat at certain points throughout the delivery system. Nothing to it! Actually, although the principle is easy, the details can be a bit more complicated and even confusing. Read on for a more in-depth description of the process.

1. The Tools

First, you’re going to need something to use as your burn material. The most common choice is pieces of index card (or poster board). Business cards work great! The considerations are you want something stiff that is easy to place and then stays in place. Also, you want something that will discolor from the heat, without bursting into flame and making a stink! Card stock works well because it is thick and can take the surface heat without immediately catching fire, like ordinary sheet paper would. Another popular option is to use wooden tongue depressors (yes, from the doctors office). Use these when your pulse is too long/hot for the index card to handle. Depressors work well when you need to manually fire your laser. But be warned, they are WOOD and will give off a lot of heat and resin when burned, generally making a stink/mess (use with good ventilation).

Second, you need a way to hold the burn material firmly in place while taking a shot, and a means of locating the beams position. For this you will need a BURN FIXTURE(s). This is normally a simple fixture made of metal that holds the burn material under a centered crosshairs and locates it in the delivery system. It usually fills the delivery path, and has a thick bottom/back plate to prevent the laser beam from continuing thru the system. Also, by blocking the path, it keeps any smoke/particles from drifting onto delivery optics further down the line. You will probably need a couple different fixtures, or some type of adapters for using a fixture at various positions in the system. When making a fixture(s) you want it to be easy to install and remove. A snug fit is not needed or desired. The fixture should be an easy slip fit into place. The crosshairs should be made of a stiff straight wire and easy to replace. Piano wire works great. Straightened paper clips also work well. Don't use copper wire, it melts too easy. They may wear out over time from the heat, so make them easy to remove and replace.

Third, some notes on the laser itself. Ideally, the alignment should be carried out with the laser running at normal operating power and temperature. What was perfectly centered when the laser was first turned on may be totally out after it warms up. The pulse used to take a burn will require some experimenting to get good results. Remember, you want to DISCOLOR the target, not turn it into a cinder! If your laser has a programmable control, write a dedicated program and keep it for future use. If your going to use manual pulses, use ONLY a MOMENTARY switch (for safety)!

SAFETY, SAFETY, SAFETY!!!!
While doing an alignment, chances are the beam will be exposed making it possible, however unlikely, that the beam may escape the system. ALWAYS make sure anyone in the room is wearing safety goggles and is aware of what is going on! Also, NEVER NEVER NEVER place your fingers or any part of your body in the beam path while the laser is on. Use care when inserting/removing the burn fixture. If a mirror is removed for alignment, always observe where the beam could hit in the room/machine when on, and take any precautions to prevent disaster! If you’re not totally familiar with laser safety and practices, DO NOT TRY THIS PROCEDURE!!!! Use this information at your own risk!

2. Alignment

To align the system, you must start at the laser source first and work your way forward to the end work piece. Any adjustment at one point will affect everything further down the line, so you MUST start at the source!

Laser head to first mirror:
Start by centering the beam coming out of the source to the first delivery mirror. Place your burn fixture at the location of the first mirror, either directly in front of it, or if the mirror is removable then in place of it. Start up the laser, allow to warm up, and then take your first burn shot. Is the beam centered on the mirror? If not, you will have to adjust the laser head to the first mirror (or vice versa). Most smaller lasers don't have an internal bending mirror, so you may have to physically move either the laser head or the mirror mount or both until they are lined up with each other. Carefully make small adjustments, taking burns after each move until the burn is centered in the crosshairs.

Fixed mirror to fixed mirror:
Use this step to align two mirrors to each other where the distance between the two mirrors is FIXED. If either mirror is moving in relation to the other, go to the next step (flying optics). Assuming the beam is centered on the first mirror of the pair, place your burn fixture at the second mirror. Take a burn shot. Is the beam centered on the second mirror? If not, adjust ONE axis of the mirror and take another shot. Continue to adjust the mirror on each axis, taking burn shots, until the beam is centered on the second mirror. Once the beam is centered, move on to the next mirror and repeat (if next mirror is a moving mirror, move on to next step).

Flying optics (fixed mirror to moving mirror):
Use this step when the two mirrors MOVE in relation to each other. This assumes the DISTANCE between the two mirrors changes in a straight line. The beam should already be centered on the first mirror of the pair from the previous steps. Move the second mirror to its FURTHEST position from the first mirror. Place your burn fixture at this location and take a shot. Adjust the first mirror (see previous step) until the beam is centered. Then move the second mirror to its CLOSEST position to the first mirror. Place your burn fixture at this location and take a shot. Is the beam still centered? If it IS still centered then you can move on to the next step. If not, then this is where things get a bit more complicated. One critical mistake a lot of beginners (and experts) make is assuming that because the beam is perfectly centered at each mirror, then everything is well. If the mirrors are in a fixed position to each other this is true. BUT between mirrors that move (flying optics) this is NOT the case. When the mirrors are moving, centering becomes SECONDARY to STRAIGHTNESS! What you want is for the beam to be hitting the moving mirror in the SAME SPOT regardless of the distance between the two mirrors. Ideally, the beam will also be centered, but this is not as critical. For this to happen, the beam must be parallel to the axis of movement. First, verify that the moving mirror is mechanically rigid and does not shift alignment when moving back and forth. Second, go back and verify that the beam is still centered on the first mirror. Now, take two burn shots, one at the furthest position and one at the closest position to the first mirror. Mark each burn to note its orientation to the system. Now place the two burns side by side and compare them. For example, is the far burn centered while the near burn is high in the crosshairs? This would indicate the beam is angled down in relation to the axis of movement. You would adjust the first mirror to raise the beam upward, and then take two more burns (near and far). Are they closer to being identical? Are you adjusting in the right direction? Follow the same technique, adjusting the first mirror, until both burns are as nearly identical as possible. When both burns look the same, the beam is parallel. And are they still centered? Well, maybe not. But as long as they're both reasonably close and will hit the second mirror without being near an edge, you'll probably be o.k. If the beam is widely off center to an unacceptable degree, then the beam position will have to be adjusted going INTO the first mirror. As in our earlier example, the beam is now parallel but high off center between the two mirrors. Adjust the incoming beam to hit lower on the first mirror by an amount equal to the offset of the parallel beam. Now re-align the first mirror to get a parallel beam to the second mirror again. Is the beam now centered better? Adjust and repeat until the beam is parallel and centered to your satisfaction.

Last mirror to focus lens:
Adjust the beam into the focus lens using the same steps as aligning a mirror to a mirror.

Verify system alignment:
Now you should have the beam aligned all the way from the laser source to the final lens. So it's time to check the final alignment of the system as a whole. Place the burn fixture at the final lens as in the previous step. You want to check the centering at the lens with the flying optics at the extremes of their travel. If only one axis moves, take two burns, one at each end of travel. If your system moves in two axes, then take four burns, one at each far corner. Compare the burns. Are they all identical? If any axis is not aligned parallel, this is where it will show up. By looking at the burns, you should easily be able to determine if there is a problem and which axis its in. Go back and adjust the system from that point forward, until the final alignment checks out o.k.

3. Final Notes

How critical is system alignment? It depends on your system and what you need it to do. A system with one fixed mirror, where only the table moves, needs only reasonable centering for maximum precision. A system with flying optics moving in two axes requires very close alignment to be precise. Each system is different and only trial and error will tell how close the alignment needs to be to get your desired results.

When taking burn shots, a shop vacuum can come in handy to remove smoke and residue. Always be careful not to contaminate any optics. One small fleck of crud can ruin an expensive mirror or lens! Avoid using compressed air; this can blow crud ONTO a mirror.

Keep a record of your alignment burns. This can come in handy later for a comparison if a problem develops.

Always verify alignment after replacing a mirror or moving/adjusting any part of the system.

And finally, BE SAFE! I won't get into laser safety procedures; there is already plenty of information on that subject. Just be sure you fully understand the risks and dangers of working with high power lasers before doing ANY work with one!

Any comments greatly appreciated...

Laser.Tech

[cncbasher]

excellent write up , clear and to the point !

dont forget Laser Glasses for the beam wavelength in use , they are not all the same !
it dont take a milisecond to be Blind , by the time you realise something is wrong , IT'S TOO LATE ' the damage is done .

[cncbasher]

can i introduce a red laser into the beam , and align to that ?

i now have a lase from the tube , which was a right pain due to some leaking o rings ! , and adjustments of the rear and oc mirrors .

i have the rear and oc window near correct i think , powered up to around 200w although i should be able to get it up to full power of around 600w.

the next problem is aligning the seperate laser cabinet to the first fixed mirror
i.e how do i know i have the laser horizontal to the axis etc

then on to the floating mirror at the top of the z axis and finaly the Lens !

you realy need patience for this job , and finding a material that can withstand 200w + to show a burn .

still a lot to learn but gradualy seeing the Light at the end !

thanks to laser Tech , i owe u a Beer !( or 10 )

[MacGyver]

can i introduce a red laser into the beam , and align to that ?

Yes, but you'll need to align the laser pointer to the beam and then makes sure it doesn't shift relative to the tube itself.

[Nitrous]

Laser.Tech's Guide To Aligning CO2 Beam Delivery Optics

Aligning a high power laser thru it's delivery optics is a basic step that is ESSENTIAL for getting the most accurate work results and preventing damage to the equipment, and most importantly keeping it SAFE to use!

The basic principle is quite simple. Put some type of material (i.e. index card) in front of the beam. Turn the beam on long enough to discolor the material. This indicates the location of the beam. Adjust the beam direction until the position of the beam is where you want it. Repeat at certain points throughout the delivery system. Nothing to it! Actually, although the principle is easy, the details can be a bit more complicated and even confusing. Read on for a more in-depth description of the process.

1. The Tools

First, you’re going to need something to use as your burn material. The most common choice is pieces of index card (or poster board). Business cards work great! The considerations are you want something stiff that is easy to place and then stays in place. Also, you want something that will discolor from the heat, without bursting into flame and making a stink! Card stock works well because it is thick and can take the surface heat without immediately catching fire, like ordinary sheet paper would. Another popular option is to use wooden tongue depressors (yes, from the doctors office). Use these when your pulse is too long/hot for the index card to handle. Depressors work well when you need to manually fire your laser. But be warned, they are WOOD and will give off a lot of heat and resin when burned, generally making a stink/mess (use with good ventilation).

Second, you need a way to hold the burn material firmly in place while taking a shot, and a means of locating the beams position. For this you will need a BURN FIXTURE(s). This is normally a simple fixture made of metal that holds the burn material under a centered crosshairs and locates it in the delivery system. It usually fills the delivery path, and has a thick bottom/back plate to prevent the laser beam from continuing thru the system. Also, by blocking the path, it keeps any smoke/particles from drifting onto delivery optics further down the line. You will probably need a couple different fixtures, or some type of adapters for using a fixture at various positions in the system. When making a fixture(s) you want it to be easy to install and remove. A snug fit is not needed or desired. The fixture should be an easy slip fit into place. The crosshairs should be made of a stiff straight wire and easy to replace. Piano wire works great. Straightened paper clips also work well. Don't use copper wire, it melts too easy. They may wear out over time from the heat, so make them easy to remove and replace.

Third, some notes on the laser itself. Ideally, the alignment should be carried out with the laser running at normal operating power and temperature. What was perfectly centered when the laser was first turned on may be totally out after it warms up. The pulse used to take a burn will require some experimenting to get good results. Remember, you want to DISCOLOR the target, not turn it into a cinder! If your laser has a programmable control, write a dedicated program and keep it for future use. If your going to use manual pulses, use ONLY a MOMENTARY switch (for safety)!

SAFETY, SAFETY, SAFETY!!!!
While doing an alignment, chances are the beam will be exposed making it possible, however unlikely, that the beam may escape the system. ALWAYS make sure anyone in the room is wearing safety goggles and is aware of what is going on! Also, NEVER NEVER NEVER place your fingers or any part of your body in the beam path while the laser is on. Use care when inserting/removing the burn fixture. If a mirror is removed for alignment, always observe where the beam could hit in the room/machine when on, and take any precautions to prevent disaster! If you’re not totally familiar with laser safety and practices, DO NOT TRY THIS PROCEDURE!!!! Use this information at your own risk!

2. Alignment

To align the system, you must start at the laser source first and work your way forward to the end work piece. Any adjustment at one point will affect everything further down the line, so you MUST start at the source!

Laser head to first mirror:
Start by centering the beam coming out of the source to the first delivery mirror. Place your burn fixture at the location of the first mirror, either directly in front of it, or if the mirror is removable then in place of it. Start up the laser, allow to warm up, and then take your first burn shot. Is the beam centered on the mirror? If not, you will have to adjust the laser head to the first mirror (or vice versa). Most smaller lasers don't have an internal bending mirror, so you may have to physically move either the laser head or the mirror mount or both until they are lined up with each other. Carefully make small adjustments, taking burns after each move until the burn is centered in the crosshairs.

Fixed mirror to fixed mirror:
Use this step to align two mirrors to each other where the distance between the two mirrors is FIXED. If either mirror is moving in relation to the other, go to the next step (flying optics). Assuming the beam is centered on the first mirror of the pair, place your burn fixture at the second mirror. Take a burn shot. Is the beam centered on the second mirror? If not, adjust ONE axis of the mirror and take another shot. Continue to adjust the mirror on each axis, taking burn shots, until the beam is centered on the second mirror. Once the beam is centered, move on to the next mirror and repeat (if next mirror is a moving mirror, move on to next step).

Flying optics (fixed mirror to moving mirror):
Use this step when the two mirrors MOVE in relation to each other. This assumes the DISTANCE between the two mirrors changes in a straight line. The beam should already be centered on the first mirror of the pair from the previous steps. Move the second mirror to its FURTHEST position from the first mirror. Place your burn fixture at this location and take a shot. Adjust the first mirror (see previous step) until the beam is centered. Then move the second mirror to its CLOSEST position to the first mirror. Place your burn fixture at this location and take a shot. Is the beam still centered? If it IS still centered then you can move on to the next step. If not, then this is where things get a bit more complicated. One critical mistake a lot of beginners (and experts) make is assuming that because the beam is perfectly centered at each mirror, then everything is well. If the mirrors are in a fixed position to each other this is true. BUT between mirrors that move (flying optics) this is NOT the case. When the mirrors are moving, centering becomes SECONDARY to STRAIGHTNESS! What you want is for the beam to be hitting the moving mirror in the SAME SPOT regardless of the distance between the two mirrors. Ideally, the beam will also be centered, but this is not as critical. For this to happen, the beam must be parallel to the axis of movement. First, verify that the moving mirror is mechanically rigid and does not shift alignment when moving back and forth. Second, go back and verify that the beam is still centered on the first mirror. Now, take two burn shots, one at the furthest position and one at the closest position to the first mirror. Mark each burn to note its orientation to the system. Now place the two burns side by side and compare them. For example, is the far burn centered while the near burn is high in the crosshairs? This would indicate the beam is angled down in relation to the axis of movement. You would adjust the first mirror to raise the beam upward, and then take two more burns (near and far). Are they closer to being identical? Are you adjusting in the right direction? Follow the same technique, adjusting the first mirror, until both burns are as nearly identical as possible. When both burns look the same, the beam is parallel. And are they still centered? Well, maybe not. But as long as they're both reasonably close and will hit the second mirror without being near an edge, you'll probably be o.k. If the beam is widely off center to an unacceptable degree, then the beam position will have to be adjusted going INTO the first mirror. As in our earlier example, the beam is now parallel but high off center between the two mirrors. Adjust the incoming beam to hit lower on the first mirror by an amount equal to the offset of the parallel beam. Now re-align the first mirror to get a parallel beam to the second mirror again. Is the beam now centered better? Adjust and repeat until the beam is parallel and centered to your satisfaction.

Last mirror to focus lens:
Adjust the beam into the focus lens using the same steps as aligning a mirror to a mirror.

Verify system alignment:
Now you should have the beam aligned all the way from the laser source to the final lens. So it's time to check the final alignment of the system as a whole. Place the burn fixture at the final lens as in the previous step. You want to check the centering at the lens with the flying optics at the extremes of their travel. If only one axis moves, take two burns, one at each end of travel. If your system moves in two axes, then take four burns, one at each far corner. Compare the burns. Are they all identical? If any axis is not aligned parallel, this is where it will show up. By looking at the burns, you should easily be able to determine if there is a problem and which axis its in. Go back and adjust the system from that point forward, until the final alignment checks out o.k.

3. Final Notes

How critical is system alignment? It depends on your system and what you need it to do. A system with one fixed mirror, where only the table moves, needs only reasonable centering for maximum precision. A system with flying optics moving in two axes requires very close alignment to be precise. Each system is different and only trial and error will tell how close the alignment needs to be to get your desired results.

When taking burn shots, a shop vacuum can come in handy to remove smoke and residue. Always be careful not to contaminate any optics. One small fleck of crud can ruin an expensive mirror or lens! Avoid using compressed air; this can blow crud ONTO a mirror.

Keep a record of your alignment burns. This can come in handy later for a comparison if a problem develops.

Always verify alignment after replacing a mirror or moving/adjusting any part of the system.

And finally, BE SAFE! I won't get into laser safety procedures; there is already plenty of information on that subject. Just be sure you fully understand the risks and dangers of working with high power lasers before doing ANY work with one!

Any comments greatly appreciated...

Laser.Tech

Ok guys,

I've got a real challenge to deal with.
I have replaced a 40W CO2 tube with a longer 50W tube. No change in power supply but this is not, I hope the problem.
We extended the chassis of the CO2 tube using a steel tool box attached to the side of the case.
Here is my problem.

When we cut acrylic, we get a beveled cut. It's not symmetrical, but rather its relatively perpendicular on one side and beveled on the other.
My best guess (using an edge-on x-y orientation) is that the laser tube head isn't absolutely perpendicular to the cut face.

I suspect that the beam is hitting the acrylic at an oblique angle ie the angle of incidence is other than 90 deg.
What should be a split between the left / right side of the kerf is not all on one side. We're using an air assist. The pressure is less than 10psi.

My problem is the following. I haven't found an effective means of adjusting the 3rd mirror (ie the mirror at the head).
This is a "cheap Chinese laser" which doesn't seem to have any practical means of modifying beam alignment at the head end.

I've done the basics ie put a cross hairs neath the output head and checking the alignment but this really doesn't deal with true x-y perpendicularity.

Any suggestions would be appreciated. I've fiddled with power setting (max of 10ma with minimum reliable current around 2-3ma) and also with cut speed.

Thanks,
Doug

[Dean448]

I think you answered your own question. People who are technical enough to know exactly what's wrong with a laser but aren't technical enough to modify it correctly, shouldn't buy units from the Chinese.


Sent from my iPhone using Tapatalk

[Nitrous]

Thanks for taking time to reply

[gfacer2]

You should be adjust the aim of the third mirror and in the middle might not be where it needs to be.

I drilled out the cone of my air assist to help get a little more adjustment room. You could also try and hit the third mirror either higher or lower to get more room to aim it perpendicularly.

Sent from my LG-D852 using Tapatalk

[Nitrous]

Thanks gfacer2,
I think I'm going to either make a 3rd mirror adjustment plate or simply replace the cheap head with a better one that has adjustment capabilities.
Doug

[Gozzie]

Do you have any pictures to go with your guide ?
I would love to see some photos of the target fixtures you use and how you mount them in front of the mirrors.

Gozzie

[consurelasercnc]

Hey friend,

Here is the complete User Video for co2 laser engraving cutting machine.

https://youtu.be/glhaw3dVNps

Best Regards

Lucy
Consure Laser

[Nitrous]

BGozzie,

One of the fellows at the local Makespace is in the process of writing it up.
Essentially, I used a 1" diameter punch from Michaels to cut out Dymo Thermal Labels. (From Staples)

The cross hairs were applied by sharpie fine point pen. I used an acetate sheet to centre the discs and mark up the lines.

The self adhesive nature makes it easy to loosely apply the targets over the mirrors. For the laser head, I made a Plastic plug that pushes into the ~1/2" hole. The face is 1" diameter so the target is easily attached. The label doesn't actually touch the mirro surface. They adhere to the mirror mounts.

Nothing really complicated but quite effective.

Doug

[gfacer2]

I just use painters tape. I don't care as much that the dot is in the centre. I want it to stay in the same spot all over the table. It should be close to the centre though. To do my mirrors, I cover with painters tape, then fire, then add a tiny additional strip of tape over top, just covering the first dot. Then I fire again and compare the two by peeling back the top layer to check it vs the layer underneath. I repeat this on each mirror (well the hole on mirror 3).

I used to do it more with targets (still used tape but tried to get an impression of mirror holder first) the but this way let's you dial in the variation faster so you end up with a nice constant path through all the mirrors and all over the table.

Sent from my LG-D852 using Tapatalk