Most paper you get out of a copier is 20 pound and is between 3 and 5 thousandths. This is pretty normal tolerance for machining parts. Plus of minus .005 is something most people wouldn't notice, but if you hold that to the whole plane, it's sure going to fly better for it. I am designing a plan in AutoCAD right now, and I have my prefs set to hold accuracy to ten thousandths. Your plans and tools should always be at least ten times as accurate as you want the final product to be.