Typical newbie mistake...
Reviving an old thread, but here I go.
At a thermoforming plant involving mostly ABS we made our own deburring tools.
Take a metal band (old bandsaw blades seemed to work best, about 12-18" in length), sharpen it in the center section like a knife on both sides (about 1-2" in length), double it over without creasing it (you want the loop to be where it was sharpened), and duct tape yourself a handle (4-5").
The tool will cut off flashing/burrs quite easily by dragging the loop against plastic edges; without much damage at all. There is a bit of a "feel" to it to keep from damaging the part, and the sharpness of the "blade" dose matter some.
Works great on ABS, PC, and rigid PVC, though we had to be extra careful on "softer" materials like HDPE. Not so sure it would be a blessing on thinner materials either.