An auxiliary subbase for wide cuts
To make a cut that is wider than a particular router bit, you would normally make one pass, shift your edge guide and make a second pass. Or, you can use this auxiliary off-square sub-base.
Cut a piece of Winch plywood into an S>-inch square. Remove the router’s sub-base and bore the screw holes and clearance hole for the bit through the auxiliary sub-base so the tool will be centered on the jig. Next, cut Vie inch of wood from one edge of the sub-base, Ye inch from an adjacent edge, and Ya inch from a third edge. Mark the amounts you removed on each side. Screw the jig to the router and make a pass with the uncut end flush against the guide. Rotate the sub-base and make a second pass, widening the groove by У16, Y&, or Ya inch, depending on which side you use.