The laser is consistently burning the top two corners more than the bottom, and it burns the bottom right least of all. This is very consistent on paper and cardboard.
We noticed this while doing the Calibrate Camera Alignment test and burning the pattern for that.
We’ve already tried aligning the mirrors and cleaning them with alcohol. When testing the alignment with tape it looks exactly centered for the most part.
Does anyone have an idea what our problem might be?
I smiled and sighed while reading your post because welcome to my hell. I know and have had to deal with this same symptom from time to time. It is such a pain sometimes to tune the optics.
The two likely suspects if you have already checked mirror alignment, cleanliness, and lens are:
Bed leveling is off Note: level / true to the gantry (not to a bubble)
In short, the distance from the bed surface to lens cone should be exactly the same anywhere on the laser bed. Take a random block of wood place it on the bed, carefully adjust z to where the cone just barely makes contact with the wood (you should still be able to slide the block out from under the cone). Now move that block and head around the bed testing different locations. (you may also consider laying a nice flat sheet of acrylic on your bed first to span the bed’s bars and make moving the block around easier / less of a hassle and more consistent).
Lens holder not plumb
If the lens holder is out of plumb, then those corners where output is lost could be caused by the laser being obstructed by the cone. A quick test for this (but not a 100% certain test) is to remove / unscrew the lens cone and test.
Also, being the bottom two are less and the bottom right is the least, I suspect a combination of your gantry mirror alignment and lens holder as the cause OR the front of your bed is really out of whack compared to the back.
I know and have had to deal with this same symptom from time to time. It is such a pain sometimes to tune the optics.