Surely, you need a shim in your shop (every woodworker does). OK, you could run to the hardware store and get some low quality shims made from pine or some other so-so softwood, OR you could craft your own using hardwood from your scrap pile. All your woodworking buddies will admire your shim collection and want to know where you got them. (Don't worry, we won't tell!)
Check out these highly detailed plans.