Cutting Dados With A Router
In this article I’d like to show you how to cut dados using a Plunge Router. More specifically this method is very useful for cutting dados in the sides of a book case. It would be very difficult to cut these dados using a stacked dado in the table saw because the work piece is so long.
A while back I wrote an article about how to build a dado cutting jig for your Plunge Router. I built this jig so I could cut dados in book case sides. You can make one of these jigs using any scrap plywood you have laying around. I ended up using some 3/4″ birch plywood that was left over from some cabinet shelves.
Router Jig Details
Basically you want to build a U-shaped frame that’s slightly wider than the book case. For me my book case is 12″ wide so I made the jig 12 1/8″ wide. As you can see in the pictures three of the pieces are permanently screwed together. The fourth piece is held in place with 1/4″ carriage bolts, washers and wingnuts.
The key to this jig is to make sure that the two side pieces are VERY square to the third side when you screw them together. If the sides are not square you’ll never be able to cut perpendicular dados in the work piece. I used a countersink pilot drill so that the permanent screws are all recessed below the surface.
I created two slots in the side pieces. The slots allow you to adjust the fourth piece for different width dados. Once you build the jig you’ll need to set it up for the dado you need to cut. The nice thing about this jig is you can cut a dado the exact width you want.
Most plywood is not exactly the thickness that you call it. For instance, 3/4″ plywood is actually 23/32″. So if you want a nice tight fit on the slots you need to cut 23/32″ wide dados not 3/4″. For more information on plywood thicknesses check out: Thickness Of Plywood Panels.
With this router guide it’s really easy. Measure the width of the router base. My router base happens to be 6 3/4″ in diameter. I’m going to use a 1/2″ straight cutting router bit. So I take the 6.75″ – 0.5″ = 6.25″ (This is the spacer block you’ll need). Cut a spacer block and set it in the jig. Now take a piece of the plywood you’re trying to match and set it in the jig as well. Pull the fourth piece tight against the spacer and plywood, tighten the wingnuts and remove all the spacers. You now have a router guide set up to cut a perfectly sized 23/32″ wide dado.
It’s as simple as that. Stay tuned for a future post on building the book case.