I've been using a Miller unit for the past bunch of years. I forget the model number. Maybe the Spectrum 375? Anyway, clean tips cut better. A plasma will never leave a super smooth edge. A worn/dirty tip will make an even rougher edge. The model may say that it cuts up to 1/2", but, if you drag or push your torch too fast, the flame will push off to the side and that's where your cut will be. Sometimes my guys will grab a painted/rusty whatever to cut. I'll usually tell them to sand off the paint as a plasma needs good conductivity. Bad conductivity will give you a bad or impartial cut. Making shapes is easy. I've made plenty of 3/4" plywood patterns that will make the shapes I need. See the image below that started as 1/4" plate and became motor mounts. Straight lines are as easy as using a piece of angle iron. Dry air line? I haven't given it much thought and have never had an issue.
