Tweakie - I know I've been saying I'm going to post things, and it's taken me forever. I'm usually farting around on my laser trying to figure out the best feeds / speeds for everything instead of taking pictures of stuff...
Sorry about that.
Anyhow - here's two small things I've done. the picture of my boy running actually looks a lot better in person than it does in the picture. Also, balsa seems to be a horrible wood to engrave in - it's so grainy. It produces some pretty nice contrast though. It was done at 375 in/min (10,000 mm/min) at about 22% power, which was probably set a little too high.
The second image was some text I engraved into some scrap acrylic I had lying around. Same settings, basically, but bumped laser power up to about 50%. Came out good. I did start finding out that I really need to turn off my air assist when I'm engraving, it condenses the acrylic vapors and leaves a fine powder all over the rest of the engraving, which ends up leaving a ghosting effect around the letters, all in the same direction, since the air is blowing out of the nozzle. Once I turned the air assist off, the problem went away. I also noticed that when I'm engraving in beechwood that I was having the same issue. Although, not leaving the air assist on led to the dust collecting all over the print and staining the really light areas when I brushed it off. I might actually make a two-way air assist for my laser, one that blows out, and one that vacuums.