I used a scoring blade #16 exacto knife to trim the pieces as close as I can. Then used a table sander to finish the edges to the trim lines. Hand sanded the edges with 150+ grit sandpaper to smooth the edges then used a utility knife to remove the burred edges. This gave me a clean smooth edge.
The helmet I did with a high speed dremel cutter for roughing out the eyes. The used a sanding wheel on the dremel to finish the eyes to the trim lines. The frown I drew where I wanted to remove the holes and drilled holes all in teh area. Then used a #11 exacto blade to finish the frown. Doing it by hand made sure I did not screw up the helmet. When using a dremel you have to be very very careful. It can get out of control in less than a blink of an eye and ruin the faceplate, or any part, before you even know what happened.