by cvoinescu » Wed Dec 05, 2012 3:05 pm
The beam from the laser spreads out with distance. When X is all the way to the left and Y all the way to the rear, you get the shortest beam path, thus the smallest beam size, so it's fairly easy to align your optics so that all of that beam makes it to the lens. When you move further apart, the beam makes an ever wider spot, so some of it may no longer hit the mirror on the gantry or the lens. That power is lost (and can damage the mirror and lens holders). If the beam is still narrower than the mirror and lens, with careful adjustment you can still get it all to the workpiece, but if it spreads out more than that, there's nothing you can do except get a larger mirror and a larger lens, or somehow improve the collimation of the beam (I'm not sure whether collimators exist or are affordable for this wavelength). It's not the focal length of the lens that matters, but the diameter; and if some energy misses the last mirror, a different lens certainly won't help. Things are also made worse by the fact that higher-power lasers have wider beams to begin with, so they are more difficult to work with or require larger mirrors and lenses.