Mirror adjustment / alignment for a CO2 laser is quite a tricky process. It usually involves placing a paper or tape target over successive mirrors and adjusting the previous mirror to centre the beam on the target – it is basically a trial and error process whilst test firing the laser.
This photo, of a slight mishap during a test fire, was posted on another forum and the owner of the finger commented: “it hurt, in fact it hurt quite a lot”.

Don’t we just have to be so careful when operating any of our CNC controlled equipment ?   

Tweakie.