4-in. plywood with a smooth surface for the router sled to ride on and broad enough to hold the pat-tern and the sled. Mine is 16 in. by 42 in. The height of the jig base is adjusted with shims so that the tip of the router bit in the sled is exactly the same height as the lathe centers. The pattern is simply a piece of 1⁄ 4-in. plywood cut ...