I just posted this info as a response to a problem, and realized it could be helpful to others if I posted it on it’s own here.
Sometimes plywood has hidden voids that are filled with glue. The laser often won’t cut all the way though the glue spots. Sometimes you can get through with another pass or two of the laser, or just finish the cut by hand with a hobby knife, but I find it best to just avoid the voids if possible by identifying where they are.
I use this worklight from costco; with the kickstand folded it lays flat on it’s back.
bb ply over the light, then turn it on. (it’s really bright)
good over here.
Big ugly glue-filled void.
Avoid this area for cuts, or allow for multiple passes with the laser. There may be significant charring of all cut edges if you run enough passes to get through the glue. I find that it often takes me 4 or more extra passes for stubborn spots, which can take a lot of time with a complex design.
Pro Tip: Turn off the lamp before removing the ply so you don’t blind yourself. It’s still really bright.