So I started on my 4th of July project and hit one slight snag, how do you cut the plastic? I want straight lines and want to make sure they come out clean. So what do you guys use?
Personally, a little bit of everything, really. Boxcutters work well if you're just looking to score a long line of plastic. I also use a cheap-o fold-out knife I got a Wal-Mart and my pocketknife. Some of the more professional folks use a Dremel with a cutting blade attached to it, but I'm cheap and lazy.
Razor saws and jeweler's saws are pretty cheap, and beat the hell out of plain knives. Dremel's are easily the best overall, but my present go-to is a jeweler's saw. Nice, soft cut lines and excellent control. Also less wasted material and no chance of plastic melt. To score longer cuts, a fresh Xacto is what to use. Score lightly, score again, then score again.
Jeweler's saw Small mitersaw and box If you use an exacto blade for scoring, try using the back of the blade (the dull side). You'll be surprised how much control and how quickly you will get clean cuts in not to many strokes. Slightly more advanced, you can use thread as a friction saw. Works great for cutting along panel lines, etc. You will most likely need a clamp/vise to hold your part as you wrap string around each first finger like dental floss and use a steady sawing motion.
Score before making your cut and use a metal ruler to keep your score lines straight. I use a Dremel cutting wheel of I don't need to be too careful (I'm going to do some grinding and sanding afterward) and a razor saw (got razor saw blades for my xacto) for the cuts I need to do more carefully. The Dremel tends to make a thicker cut and makes a bit of a mess with the melted plastic being kicked out to the sides but it takes much less effort and goes quickly.