Can I ask what the material you use is? I have found that polystyrene sheet tends to melt along the laser cut edges, what kind of plasticard are you using?
It's not my laser, I buy time on geronimo's (fenris games). The material I use on my kits is just standard extruded polystyrene (plasticard), Geronimo sources it for me. Yes there is some melting but I only use .5mm and 1mm sheet thicknesses, so it's a very small amount, and I build that into the geometry. Thicker sheets would be problematic with melting I believe. I understand the only issue with cutting the styrene is that you need good ventilation as the fumes are toxic.
For those of you not familiar with the kits I sell, you can see them here
http://brandlin.blogspot.comI'm always on the lookout