Rip two pieces of 3/4" plywood, not oak, but fir or cheaper, preferably scrap, 3"x36" and two pieces 3"x16". Measure the base plate diameter on your router. Make a box with the short pieces on top of the long pieces, as shown. X equals the measurement of your router base plate plus 1/4". Use a 1/2" router bit. When the router is guided by the long pieces, it will make a 3/4" dado. Try it out on a piece of scrap and adjust the width to suit your 3/4" plywood for ease of fit, not too tight, yet not too loose. Mark the edge of the dado in relation to the edge of the router guide and use this measurement when setting up to router your dados on the side. Remember when laying out the dados, lay them out on the worst side of the sheet of plywood and as a mirror image to each other unless, of course the gable end is against the wall. When constructing cabinets with dadoed in shelves, I make them exactly 1/4" deep. Notice that the end pieces are on top of the side pieces so that the router base will be able to go under the ends. Either use clamps to hold the router jig in place or small finishing nails.
Dave(Ask Dave) (About Dave)
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