All of the beam energy has to land across M1’s exposed mirror surface. It can tolerate being a little off. But some of the beam energy is outside the diameter that is intense enough to burn tape, you don’t want to waste it. This may already be capturing it all, though
So, it’s a little high. Being forward also means when the beam comes down the Y on the left (rear to front), it will be a little further to the left.
In a system done with loose tolerances, you need to look at the whole system. If it’s hitting M2 dead center as far as left-right is concerned when M2 is at either limit, then M1 is aligned but offset a bit. If you just move M1 to the front of the machine to get it centered better on M1, it will not be on center on M2 anymore and you might have to change the mounting offset of M2.
That’s if you were to move M1 to the front of the machine. If instead you just shift it to the left, that will get the beam centered on M1 without offsetting where the beam goes down the Y.
Thus aligning it first and seeing what offsets might be needed second is a sound strategy. It’s not the only strategy.
The z height being high, you actually do need the system aligned first. Because the overall XY plane of the gantry “is what it is”. If you pulled up all the gantry rails and put a shim washer under each one, sure, you could offset it upwards, but we don’t do that. The Z height of the XY plane is already determined by placement of M3 and M2. Think in reverse, it’s equally true- if the beam starts at the lens, hits the center of M3, M3 is angled to hit M2 dead center, then M2 can only be adjusted to be parallel with the Y rail as it goes back to M1. Anything else would be wrong. If it hits M1 too high, that’s the prob. Nothing about the angle of M2 or M3 affects that. Offsetting the mirror locations would, but we’re not going to do that.
This is probably not an M1 angle issue, or any mirror- the tube is off. Tube mounts usually have Z lift screws and a locking screw. Undo the lock screw and move both down, or only the one closest to the mirror lower or only the further one higher. The second two options change the angle of the beam before it hits M1. M1 can be aligned all the same to get the beam dead center on M2, it won’t care.
Generally speaking you want the tube “level” of course. If you find the tube isn’t level to begin with and one of those single-mount adjustments gets it centered on M1 while lessening the angle, you’d of course favor that one. “Level” can be subjective though- generally speaking we’d be defining it as equal height of the two mounts to the horizontal sheet metal they’re attached to. But that sheet metal itself may be “off”. Doesn’t matter that much which way you go, though.
Or, well, it CAN be that the tube is already coplanar with the gantry xy plane and M1 alone is simply mounted low. On some mounts the whole combiner assembly is on a rod fixed with set screws and it can be moved up and down a small amount Low can also be compensated by putting washers under the mount, but some I’d have a high threshold of evidence that the mirror’s location is the issue, but it does happen.
