I have a strange alignment issue. I think it’s machine problem, but hopefully it is fixable. All three corners, left back, left front, right front, are aligned spot on perfectly to the center of the 3rd mirror. When i move the cutting head to right back position, the pulse on third mirror is off. If i adjust the second mirror to aligned at back right same to back left, then i miss the other positions front corners
Is this a guide rail issue, leveling issue or am i doing something wrong? The photo is from back right corner
Angular adjustment to put beam parallel to the axes
Linear adjustment to center beam on mirrors
Everybody (myself included) starts out thinking that adjusting those little screws on the mirror mounts is all it takes.
The complete process starts by twiddling those screws to adjust the mirror angles so the beam burns a single spot at both ends of the axis travel. Mirror 1 determines the Y axis alignment and Mirror 2 covers the X axis. Do the Mirror 2 adjustments with the gantry at the rear of the platform, closest to Mirror 1.
With good angular alignment, you then move the mirror mounts parallel to the XYZ axes to center the beam on the mirror. This will inevitably wreck the angular alignment, so you must iterate a few times as you approach the proper positions.
Then you tweak Mirror 1’s angle to fix the Fourth Corner problem so the spot on Mirror 3 (or the laser head aperture) in the right front corner matches up with the right rear corner.
It’s kinda tedious the first time through, but as with all such things it gets easier as you gain practice.
Now, if you’ve already done that, then the machine might have a bent frame or some other problem, but getting the mirrors set properly will help in the diagnosis.
Thanks. I will check your guide. But i think that as i aligned the mirror 2 to 3 perfectly parallel in front position, it should be parallel in back position too. It makes more sense that the machine is bend or something, or it was wrong manufactured from the beginning from the manufacturer. I bought it used, so I don’t know if it was wrong from the beginning or not
That is the Fourth Corner problem in a nutshell: everybody thinks that’s how it works, but it doesn’t.
St. Sadler’s videos go over this in mind-numbing detail, but (AIUI) the gist seems to be you do the M2 → M3 (X axis) alignment at the rear of the platform, then tweak M1 very slightly to fix the M3 entry point with the gantry at the front of the platform.
Basically, you must get the first three corners correct, including moving the mounts to adjust the beam position, then tweak the beam into place in the right-front corner.
There are no shortcuts, at least not for the first few iterations.
Notice I stated a very very small amount… you have to be smart enough to figure out what the result are and if this is working – and not screw up the rest of the alignment.
Don’t be heavy handed - use you brain … and pay attention.
So basically i will try to fix this by small movements of M1, and if i manage to correct it, then i should make a final alignment to hit M3 center moving the tube without touching the mirrors
It is impossible to move the tube without screwing up everything else, so you do that as needed while getting the beam centered on the M1 and M2 mirrors. If the tube needs moving to align the beam on M3, then you start all over again at M1.
When you’re done the steps as described above, the beam should be centered on all three mirrors and produce a single spot at the end of the X and Y axis travel, except for possibly in the right front corner. If it’s out in the right front, then you adjust M1 very slightly to hit M3 dead center.
There are 3 additional parts of an alignment that most guides leave out
The gantry needs to be squared. This is the pulley timing on the rod linking the left and right sides. If it’s off, vertical lines will not be at 90 deg to horizontal, and a square will cut a rhombus. This is difficult to measure accurately without taking up a lot of stock. One efficient way to do it is burn a large diagonal line and measure how close its length is. But you don’t actually even need to cut a line- you can just cut an “X” in two diagonal corners and measure between the centers. Ultimately you want be be able to take a sheet of plywood the size of the full bed, cut a slightly smaller rectangle out of that, and flip the rectangle upside down over the Y axis (not over X and Y) and fit it into the frame it was cut from.
The tube’s mounting Z height needs to be able to hit the #1 mirror coplanar with the XY plane. You cannot correct for this by adjusting the mirrors. Either both mounts can be raised and lowered, but also just adjusting one mount to shift the angle of the beam from tube to #1 until it is on the XY plane when it hits #1, and #1 will be trimmed normally to direct the beam on the XY plane.
To get this right, note that #1’s mounting may be a little high or low on the XY plane so dead center on #1 might not be be what you need. If #1’s center is 2mm above the XY plane, you might be able to adjust its mount down by 2mm- that’s best- but there’s enough room on the mirror to hit it 2mm below center without clipping the beam
The point where the beam hits the #1 mirror must be directly inline with the Y axis. If the mirror mount was installed offset to the left or right, angular adjustments on the mirror won’t work. The tube mounting position can’t really cause this error nor can it correct it- moving the tube left/right does nothing.
The last two of those came as a big surprise for me: all of the mirror mounts were so far off-center and the tube was far too low to get the beam into the laser head on center.
After a bunch of false starts, I had to raise the tube by about 5 mm, move M1 10 mm closer to it, then chase those adjustments out to the laser head.
It was, as they say, a Learning Experience.
That’s how they built it and that’s why I tend to be overly cynical about factory QC in the consumer-grade laser field.
I’ve never seen this done with front mirrors,… All the people I’ve seen, at 0, 0 being upper/left, they use upper/right for this. I think I quit checking this a couple years ago and just use the front three…
Next time I speak with one of these wizards, I’ll query them about the necessity of this.
There is a distance difference the beam travels as @ednisley mentioned, but I don’t know what else easy we can suggest.
I’m sure mines not perfect in all fours, but it seems to work well enough it hasn’t shown up as an issue…
