Please review page 30 of the Full Spectrum ProLF 36x24 Laser Manual for instructions on how to Manually Focus the laser cutter/engraver:
http://fslaser.com/files/36-48pro_manual.pdf
I have sent a request to Full Spectrum for the file to cut a new focus ruler - to be sure of the accuracy; but, I’m not sure how long it will take to get a response. I will try to cut a new Focus Ruler to be used later tonight to at least give us something to aim for. As soon as I get a copy of the actual file and get a confirmed accurate ruler cut, I will let y’all know.
NOTE: If someone would like to try to cut one before I can get there later tonight, please feel free. We should have a 2" lens installed at this time. Use the instructions on how to manually focus as a beginning point in designing the ‘replacement’ focus ruler. Thanks!!! 
Focusing
The laser must always be in focus when in operation. Not only will you not have full power but low power out of focus laser beams will burn or start fires instead of cutting through materials. Focusing the 24x18 is quick and easy. Your laser included a focus ruler sized for the included 2-inch focal length lens. To focus for engraving or cutting, simply place the ruler on the top of the engraving plane and jog the Z table up or down until the small notch rests evenly with the flange of the air nozzle
Figure 15 - Using the Focus Ruler
As an alternative to the focus ruler, you can use the included autofocus mechanism. FSLaser recommends using the focus ruler to achieve best results. Note that for thin or delicate materials you should always use the focus ruler.
Thanks!
Lisa
Laser Committee Vice-Chairperson