The eternal problem with beam setting has been the "4th corner" There is a well tried and tested beam setting procedure that works very well in principle. In practice there are many instances where after setting 3 corners perfectly, when you check to see where the beam is landing on mirror 3 at the 4th corner, you discover that there may be a significant error of several millimeters. THIS IS NOT A MECHANICAL PROBLEM, but an issue where the beam has been deflected to a different path, For several years I have pointed to the flimsy mounting bracket at mirror 2 as the root cause of this problem and when people fix that problem (usually be adding an extra fixing screw ) or re-fixing the cable chain, the problem can be cured. Recent design changes I created for the mirror 2 mounting bracket have made it so stiff that I MUST have fixed this issue for ever. Wrong. I have had to go back to absolute basics and try to understand just how it is possible for the beam to be deflected so much after what appears to be perfect setting. It turns out that there is a vital setting step that is missing from this long established procedure . Add this step and it will fix your 4th corner problem.
