Adjusting the Optics
The Lasersaur has three mirrors and one lens. Each mirror mount has two angular adjustments and the lens mount has one linear adjustment. The procedure starts with the laser tube and then moves along the beam path to mirror 1, 2, 3 and finally the lens. Each step's goal is to direct the laser beam into the center of the next mirror/lens. Additionally the laser beam must be perpendicular to the motion of the gantry. This is necessary because you want the beam stay in the center of the optics over the full range of motion.
BE AWARE this is potentially dangerous. Make sure to wear CO2 laser protection glasses, have access to an all-off switch/plug, and have sensitive materials out of range. It's also a good idea to first aim the laser at a non-combustable target (brick, tile) and get some feel for the whole system. Does the laser work as expected? Is the software running smooth?
The laser beam has a wave length of 10600nm and is therefore invisible. A cheap and practical way to find it's location is to use a combination of cardboard and painter's tape. A short laser pulse will clearly mark (and possible burn through) the cardboard/tape. Once you have narrowed down the location with cardboard the basic procedure is: (1) tape (2) fire laser (3) adjust (4) repeat until the laser beam is where you want it to have. The short laser pulse can be generated by sending the G-gode for a very short line cut. Something like:
S40 G91 G1 X10 F500 G0 X-10 G90
S40 sets the laser intensity (0-256),
G91 switches to relative motion,
G1 does a short cut at feed rate
G0 moves the head back without cutting.
G90 switches back to absolute mode.
Before adjusting the laser tube make sure the mount plates of mirror 1 and 2 have matching left/right position. If you were to make an imaginary line from mirror to mirror this line should be parallel to the frame.
The only requirement for the laser tube is to hit mirror 1 in the center. To be precise, it should hit the mirror 3mm above the center. Both mirror 1 and 2 are mounted slightly below the beam level (see CAD model for details). For this adjustment it's best to take out the mirror and attach the tape directly on the mirror mount.
You have now a laser beam that hits mirror 1 slightly above the center. From there the beam is reflected approximately 45 degrees. The goal is to get the beam dead center through the loop on the y-cart. By cardboard-technique get it inside the loop from where you continue with the tape.
Before moving on to the next mirror make sure to check different position of the y-cart and verify the beam does not wander as the cart moves.
Repeat the same procedure for mirror two. This time the beam has to go dead center through the opening of the mount component of mirror 3. Again, make sure the beam is in the center for both extreme positions of the x-cart.
This is the easiest one. Without the lens mounted, make sure the beam exits the vertical pipe in a concentric manner.
The lens should face curved side up. Height adjustment is work piece dependent. For a 75mm lens the flat bottom of the lens has to be 73.3mm (back focal length) from the work piece for optimal focus on the surface. This is 63mm (2.5") from the end of the pipe. Some thick materials like plywood also benefit from setting the focus in the middle of the sheet. Acrylic on the other hand can typically be focused at the surface because the material functions as a wave guide when being cut.