The spacer blocks are critical for this process to work correctly. You need two that are slightly thinner than the diameter of the cutter you’re using. We’ll call these bit spacers. Because plywood tends to run undersized, 1/2 in. plywood works well with 1/2 in. bits. You need another set of spacers that are slightly (1/32 in.) wider than the distance from the edge of the cutter to the edge of the router base. We’ll call these base spacers.
Category: Jointing with a Handheld Router.