Since CO2 lasers are invisible to the human eye it is very tideous to calibrate the mirrors of the chinese K40 CO2 laser cutter. I made this nozzle to clip on the front of the laser tube. Inside the nozzle you can mount a small, regulated laser diode. I used a battery pack to power it with 4.5V which is enough to emit a strong visible red light. With help of the mount the laser will shine directly onto the mirrors and you are able to roughly adjust the mirrors for the CO2 laser.
Prints pretty unproblematic.