I'm cutting the bottoms off plastic bottles, which is easy enough. The part I'm having trouble with is cutting around the 5-petal-type design on the bottom because the plastic is considerably harder than the sides of the bottles. I have tried an x-acto but the plastic is too hard and I don't want to slip and slice myself. I bought a hot wire cutter for foam and that's leaving a melty bead. I don't want to sand or saw, I want the edges smooth. Suggestions?