Vertical Mirror 3 Alignment. Red & Black Laser

Im looking for a CO2 laser alignment genius!

My issue is Mirror 2 to mirror 3 I get a vertical gap from the near to far point.
3 out of the 4 points are level, the far right point is always high.

I have changed the angles of the tube, removed and replaced both mirrors and adjusted all of the screw, all without any change to the gap.

Ive spent a few weeks messing around with everything on my machine but have not come across anything that shifts this damn dot at all.

I have an 80W Red & Black Chinese CO2 laser, 500x700 workbed.

Is this an Y axis adjustment that needs to be performed?
Not sure where to start with doing that.

It looks like you might have been working using documentation from Smoke & Mirrors? Remember to work from mirror 1 to mirror 3, so check you’ve good alignment mirrors 1 to 2 first. With alignment you are looking for consistency rather than accuracy… that is you’re aiming for the dots to hit together and not in the center.

In your photos, you have masking over the head/mirror 3 and 2 dots on the tape. I assume the lower dot is with the head all the way to the left of the gantry/work area and the upper dot all the way over to the right?

You’ve a tick mark on the front right of your machine, so does that mean your dot is hitting correctly at the front right, but not at the back right? In that case your issue is mirrors 1 to 2 or the angle of your tube. You could do some pulses/tests down the center of your machine or the same tape test from mirror 1 to 2 to check.

The thing to go for here is the dot hitting in the same place, regardless if this is in the middle of mirror 3’s aperture. Once you have those dots in the same place (even if not in the middle) you can then adjust the tube (if needed).

If on the other hand you are saying the dots hit in the right place right across the working area but only at the extreme right side it splits off, then you’re looking at a hardware problem of some kind.

Why do you ask about a Y axis adjustment? You’re working (if I’ve understood) entirely on the X axis?

Lastly, alignment is hard and can be frustrating. If you’ve had the mirrors out, double check they’re firmly and flatly seated. I’d also consider putting a bit of tape on the back side of your tape target, so as not to blow hot tape adhesive all over your mirrors when you pulse/shoot the laser.

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Hey Dominic

Cheers for your reply!
Sorry for the confusion, the X on the diagram is the point where the dots dont overlap on the 3rd mirror.
Yes the problem is on the extreme right side, not between mirror 1 & 2.

I have followed a few burn tests and im pretty comfortable with the mirror adjustments now, as you said I think the problem is mechanical, but i have no idea where to start with that!
I have had a look into how to raise the right side rail, but didnt want to start shimming it up and potentially causing more problems if there is an easier way to do it.

What result do you get in the centre of the bed as opposed to the very edge? Is there a point where everything goes off? I’m suggesting getting dots across the entire bed… or at least I’d like to see those.

You could shim the rail, personally I’d be asking the supplier about this issue if its a new machine.

I have just been focusing on the edges of the machine, I will try a few points across the machine and see if its a gradual rise.

Its an Ebay machine I got in November, but ive done a few mods to it already, Compressor and exhaust so its not something I could return.

Happy to fix it myself if I just knew where to start

I’d want to be sure there really is a mechanical issue before I started shimming the rail. which I guess is what you are asking. Get yourself a decent chunky (i.e. thick) square and check everything is nicely squared, that mirrors aren’t moving about when you move stuff and that nothing like chain guides, tubes/hoses or wires are getting in the way of your beam too.

Good luck. These things can be very trying.

Cheers mate =)
I knew getting into this the Chinese Lasers need a little bit of work.
I dont mind the struggle, I have learned heaps about the machine already.

Besides being one of the best videos on alignment, Russ explains how to deal with the fourth corner anomaly at about 33:10.

Any time you do an alignment, start at m1, while you’re there, ensure you’re tube is producing a TEM00 mode output… If not, it will never align properly.

Good luck


Hey Jack

Thanks for your comment mate.
Ive watched a few of Russ’s videos, he has been a great source of information.
Unfortunately his only mention of the fourth corner anomaly is adjusting M1, in my situation i have had no gap change from the 2 most extreme points.
Always starting at M1 and I think my beam is looks TEM00.

I have ordered a reverse alignment tool, so i can take a second approach to this, following Russ’s other videos.

Thanks again, appreciate any suggestions and information

Good luck with this…

I don’t think it’s going to be accurate enough to fix this issue.

Always willing to learn, especially at your expense :crazy_face:

Let us know how well it works out.


Hi Chris,
there is an easy way to check if your rails are coplanar. you can stretch 2 string lines diagonally from the back of each rail to the front of the opposite rail. if the lines do not touch each other in the center then they are not coplanar. if they do touch then swap them around so the line that was underneath the other line at the center in now on top. if they still touch in the center they are coplanar.


That’s an awesome idea, I will give that a shot

Thanks Rob!

I use the method behind the reverse alignment tool and am convinced that it’s the best and fastest way to align all mirrors on a laser. Assuming that the laser is mechanically sound. Let us know if you found it useful.

Finally had another good crack at this the last couple of days,

The middle of the machine aligns and the upward drift starts 150mm from the top right corner.

The string trick came up showing all the corners of the rails are level.

I did try and shim the rail to see what results I would get, and surprisingly it didn’t change a thing, the 2 dots wouldn’t get closer together at all, so it really seems like a mirror alignment issue or something else.

I started again and pulled out and replaced M1 & M2 and did the burn test, but still get the 4th corner anomaly, im yet to try the reverse alignment tool, I know it probably wont be the answer, but willing to try anything at the moment.

Is there anything else that could possibly effect this one corner?
The laser head doesn’t have any vertical adjustments that I can see,
The belt drive closest to M1 has a heap of washers on it from manufacture that looks strange.

Try the reverse alignment tool. Even if mechanically the machine has problems, you will at least be able to see more clearly what’s going on. Post if you have questions on how to do it.

They probably haven’t had the right length shafts in stock :wink:

I will try to find out if the nozzle is perfectly vertical compared to the gantria (in both directions), if not, it should be loosened and fed with strips of thin material.

The standard mirror holder aren’t designed to move, only angle. The goal is to form a plane with the axis of the tube and m1 thru m3. And slides are parallel to that plane. I have risers on my mirrors also. You might want to get that straight first, if you don’t trust it.

This is where a laser level helps. The ones that project a line. You can use a standard level on the tube.

The nozzle only has to be square with the bed. Because you want cut walls to be square. But it’s not that important if your cutting decorative parts.

We have same problem, i struggle few days calculating all the measurement. :woozy_face:Tries to many ways, Same result last 4th corner shot abit higher than the center.

Just found out the problem is ‘tube sitting position’ maybe too high🤔

I align 1st upper left corner, 2nd lower left corner and 4th upper right corner center.
And the 3rd lower right corner will be not center, down around 1-2mm from the center.

Then i lower back tube and raise front tube until the pointer aim the 1st mirror around 10 or 2 o clock. All the pointer will be leveled but not center. The pointer will aim abit higher from center.

Then. Just focus center m3 all 4 corners

1st & 2nd corner pointer, adjust from the 1st mirror thumb adjustment until 1st & 2nd aim center
3rd & 4th corner, pointer adjust from the 2nd mirror thumb adjustment.

At last, my mirror 1 & 2 not center :sweat_smile:. But my m3 all 4 corners centered.