#3 Mirror Alignment Question

This is my first mirror alignment and I have a quick question. I have watched lots videos and read tons of how to’s but am unsure about something. Much of what I have learned is that mirror 1 and 2 do not need to be perfect, but mirror 3 is more critical. Much of what I have seen the laser can hit the #3 mirror high but ideally it should be centered horizontally. Is this an accurate assumption?

My #1 and #2 mirrors were very close to center but my #3 mirror is slightly off to the right of center. That is the closest I can get it and having the laser dots on top of each other at both ends of the X axis. The only way I can think to get it closer is to move the #2 mirror assembly toward the back of the machine just slightly. How important is it to get this mirror centered horizontally? I would think that it would be very important because I do not see how you could even have a chance to get close to the center of the lens (without coming in at an angle) if it is off to one side or the other.

Disregard the burn spot on the left edge. That was a previous test. I just moved it over to run this test.



If they also overlap like that at both ends of the Y-axis travel, you can declare victory.

Then you should verify the beam goes down the centerline of the laser head and emerges through the middle of the nozzle:

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Yeah I think I got X and Y overlapping good. Definitely a lot of back and forth but I think I am getting close. I just have to do some further testing at the extremes to make sure it is the same all around the table.

Here is where I ended up coming out of the nozzle.

Looks good to me: declare victory!

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As others said … VICTORY. IMHO aligning the beam can be very frustrating, but u have the process down. The key is get mirror 1 close to center as possible ( may have to adjust tube in extreme cases - - On mine i had foam strips on the tube saddle that eventually relaxed and put me out of adjustment … Just saying . A laser enginer who I know and respect told me sqaure up the machine , then adjust near to far up top - get that close as can be ,then ,then go to bottom and near to far … same process … then he says …well you can cheat and put the nozzel in the middle … and see where your shooting- THAT has to be as close to center as can be and then work "BACKWARDS " Other thing I would say is make sure the lens is perpindicular /square / to work surface … if the nozzel is tilted , the beam might shoot to center,but output might be hitting a “side” at the exit … Usually u can tell if that happens if you make a “crescent” instead of a “dot” … Every one play nice and be safe enjoy the holiday!

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There’s a video on this site. Probably can’t do better than this.

Did you draw the circle around it?


Good luck


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Before I aligned the mirrors I was not getting the crescent moon but instead I was getting a line or a slash mark. I had never seen that before. You can see in this pic all the slashes. Those were pulses. The strange thing was that when it would cut it seemed to work fine (see the three lines) although maybe not as powerful as it should. I haven’t tested since aligning the mirrors yet. The crazy thing is that when they delivered and set it up, that is how they set it.

HAHAHA. It totally looks like it. No I used a lumber crayon to mark the edge. I found it challenging to get a decent outline of the edge so I came up with a way to mark it better. As I put the tape on I press firmly around the edge slightly indenting the tape. I then used the flat side of the crayon and rubbed it across the flat face of the hole evenly going right over the hole. Seems to do a decent job. At least on mirror 3, the laser tube and the nozzle. I have not tried it on mirror 1 or 2 yet. May not work as well as they are more difficult reach.

Thanks again for the guidance guys! Now onto the next

I have a different head/lens than you do. When I check vertical alignment I use this on a lens tube.

No more marking the table and fiddling around…

When you pulse these, back off the power. You see more with less power.

Dark brown center going to white…

Russ Sadler advised me to ensure m1 → m2 is the best possible and catch the beam with m3.

In the end it should go down the center of the tube and strike the lens. If the beam strikes off center it will come out at an angle to the incoming beam.

You have to have a Z adjust adjust on m3 to move the impact across the X axes of m3. Similarly you m2 needs a Y adjust for m3 Y axes. Most machines don’t have these … can’t really see how you m2 is in there, but it looks like you have some Y adjust?

I limit tape to check alignment of an object as a double check…

I viewed a high speed video of a 50W pulse using masking tape on m3. The pulse produced a nice brown spot. The high speed video showed the cloud of adhesive that was vaporized a majority of which ended up on m3 :face_with_spiral_eyes:

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That is a nice setup. I have been trying to determine what tools to get/design to help make the alignment process easier and quicker. One of these days I will spend more time on that.

Yes I believe those grooves allow the M2 to move back and forth on the Y axis. I am not sure on the M3 though. I will have to look at it tomorrow to see. Although I feel like I got the X & Y axis overlapping nicely and my laser comes through the nozzle exactly like that at all corners of the table, I still wonder if the laser coming out will be straight vertically. I have not cut anything yet since those adjustments but I will know soon enough.

Yeah I do not like that at all. I remedied this by triple stacking tape for all tests (M1, M2, M3, laser tube) except the nozzle, which is probably the worst one to have, because all the debris floating around and landing on the lens. I will find a better solution one of these days.

Thanks for the info!

I’m going to steal some of Jack’s thunder. Here are a couple of pics of Jacks technique for targets. You can make targets out of card stock and cut them with your laser, this would eliminate the cloud of adhesive that Jack is talking about.

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Yeah that is kind of what I am thinking about. I have come across a handful of ideas out there. I just need to sit down and think it through.

Thanks for the idea.