Following the same idea as this previous post, it I stumbled on this company that has the same concept for turning your 3D Printer into a low power laser cutter/engraver.  They appear to actually have a kit ready to go now which seems to focus primarily on the old Makerbot thing-o-matic, but I’m sure can be adapted to other designs.

The laser is mounted in front of the plastic extruder, and the 2 watt laser driver board is tied to the motor on/off signal from the existing electronics.  From there a little special G code is required to get it going .

Check out a video of it cutting 1/32″ wood with a 445nm Blu Ray laser after the break.