You should be able to lay the balsa right on top of your plans to get the angle correct. I'm assuming your building right on top of the plans(don't forget the wax paper over them). I keep one of those boxes of 100 razor blades on my table and just push it straight down thru the balsa. When they get dull toss it and grab another. I think I paid $3.99 for a hundred. I keep a miter for spruce and bass wood. Good luck.