Learn how to make a simple router jig for cutting dado slots. This simple jig makes it easy to cut accurate dadoes with a router. This jig is easy to build and simple to use.
Chris Marshall: Hi folks, I’m Chris Marshall, with Woodworker’s Journal Magazine. One of the strongest ways to install shelves in a bookcase — like this one — or a cabinet project, is to fit the shelves into dadoes in the sides. But to do that, the dadoes need to be cut perfectly straight and to exactly the right width for your shelving material. (And when I built this bookcase, I also needed the shelf dadoes to stop right here. Those can be tough to cut accurately with a table saw and dado blade.
CM: So for stopped dadoes like that, I reach for a simple-to-make slotted dadoing jig for my router. Here’s the one I used for the bookcase project. It’s got a platform to support my router base, with a slot down the middle that fits a 1” outside-diameter rub collar mounted in my plunge router. The jig’s base rests against the edge of my bookcase or cabinet side panel, and it squares the long slot across the panel when I clamp it in place. And if you look here, there’s an even deeper slot cut into the base. That’s made by the actual router bit you’ll use with the jig. It will show you the exact position your router will cut the dado slot, so it’s a SUPER handy index to set this jig accurately.
CM: And once the jig is clamped in place, this slot makes sure that my router can’t drift off course when I’m routing my dadoes, because the rub collar can only go in one direction — straight. With this jig, you’ll always rout dadoes with confidence —whether you’re building a bookcase or another shelving project. And in this short video, I’ll show you how to build one of these jigs.
CM: Start by cutting two, 6-in.-wide platform pieces from 1/2”-thick MDF or plywood. I made mine 26” long, which will allow the jig to cut dadoes up to about 18”. But, you can make the platforms however long you need them to be for your projects. (Flipping jig over to show) As you already know, you’re going to need a base piece for the jig. Make it from 3/4” scrap, 3” wide and exactly 13” long. And you’ll also need this 13”-long bridge piece too, to secure the platform pieces at the end of the jig. I made my bridge 2-1/2” wide.
CM: Start assembling the jig by brad-nailing or screwing one of the platform pieces to the base piece, flush with its end. Attach the bridge piece in the same way to the other end of the platform, but this time, to its opposite face. Now we need to fit the jig to our router’s 1” outside diameter rub collar. This will be the dedicated size that you’ll always use with this jig. For the next step, grab a steel rule or a scrap that measures exactly 1” wide. I’m going to set the second platform piece into position here, and then set the rub collar between the platform pieces, over the base. Now, I’m going to slide my steel rule between the platform pieces on the other end, under the bridge. That establishes our 1” slot.
CM: Now clamp the second platform in place carefully, making sure that the slot doesn’t change. Then nail the parts together to secure the second platform. If you’ve built the jig carefully, the rub collar should slide in this slot without extra play. There’s just one last step to do before your slotted dadoing jig is ready for use. Install a bit in your router that you plan to use with this jig. I’ve got a 23/32”-diameter straight bit in mine. It cuts a dado that’s the perfect width for today’s undersized 3/4” plywood.
CM: Now install the rub collar and set the router for a 5/8”-deep pass. Rout a slot across the base of the jig on top. Put a piece of scrap wood in front of the base, underneath, to keep the bit from splintering when it exits this cut.
CM: And now you’ve got your indexing slot, so you know exactly how to line this jig up for cutting dadoes. That’s it! Oh, one last thing: it’s not a bad idea to write the bit size, and rub the collar size, right on the jig — so you’ll remember what to use with it, later. These slotted jigs (B-roll) are my FAVORITE way to rout dadoes. Quick, easy and accurate! I hope you like yours just as much as I do. And, if you liked the looks of the bookcase [B-roll] at the beginning of this video, you can find free, downloadable plans plus a video that will show you how to build it, by visiting woodworkersjournal.com. Thanks for watching.