Laser alignment woes

[Kingdomoffurr]

I have a aluminium extruded frame laser cutter home brew build and I am having some minorish alignment woes..

Everything and I mean everything is level, its been checked and double checked. That goes for the frame, bed, parts of the frame, gantry, tube, laser head etc etc.. I am now a seasoned pro at lining the mirrors up having played around with them over and over again.


So, this is my problem. Rear and front left of the bed, laser hits the aperture of the laser head right in the middle( great). Front right, as normal, mirror 2 has to be aligned so that it hits the same spot as front left and rear left.. However...
Rear right the laser is hitting the aperture high, not at the same spot. Apparently even expensive machines you'll never get it bang on and there is always an alignment of best fit.
So to compensate I have had to make sure that the laser hits slightly low at the front right, so that it hits in the middle of the aperture at middle right and not too high at rear right.

I'm currently at a loss as to how to get it hitting exactly the right spot all the way around. I think there must be a very very tiny twist in the frame on the left or right that the gantry runs from rear to front on. Its probably miniscule but over 1.2m its enough to be out by 5mm.

Does anyone have any ideas? Am I being over fussy and this is normal? See pic attached and you can see the difference between the front and the back. Moving the mirror makes no difference since the distance stays the same.

Note, the image has been auto rotated for some reason.

[cvoinescu]

That means that your mirror rotates slightly as it moves along the rails, or, more likely, that your frame is not in a plane (the rear-right and the front-left corners are lower than the other two). If you used a spirit level, that's probably not accurate enough for this job.