Zero Clearance Dado Jig
While working on a cabinetry project I needed to rout dados on 7' long panels. This means I needed to bring the tool to the piece. I can use a straight edge of some type and a clamp to get this job done but on every cut, I would have to measure for the offset of the base which introduces the possibility for human error. I decided to make a zero clearance jig to help make this task not only repeatable but fast. I measure on the panel for the top or bottom of the dad and slide my jig into place and it's ready for the cut.
The jig is super simple to make. The fence portion is 12" long and the perpendicular rail is 18" long. Both pieces are 3" wide and are made out of MDF. To attach the rail to the fence I first used CA glue and activator to create an instant, but temporary bond so that I can install 1 1/4" screws. Next, I needed to create the zero clearance cut and this part is important because it's going to make this jig unique to whatever setup I'm using. I used a 23/32 router bit for 3/4" plywood because oftentimes 3/4" plywood is actually a little thinner. This router bit is specifically made for 3/4" plywood that I picked up years ago.
Parts used in this build(affiliate links below):
23/32 Router bit: https://amzn.to/2EOoBlP
Bosch Plunge router kit: https://amzn.to/2EOsPdk
CA Glue: https://amzn.to/2Hr1Ffe
CA Activator: https://amzn.to/2C9bESX
Wood Glue: https://amzn.to/2EU1ZAB
I used a scrap piece of 3/4" MDF to make the jig. First step is to rip it down to a 3" strip.
Now I can cut the two pieces out of the strip using my miter gauge and a stop block. I first set the stop block to 18" and cut the piece.
Next I move the stop block to 12" and cut the second piece.
Before I can install screws I need to temporarily attach the rail to the fence. I used my miter gauge fence since it's a known flat surface.
A few drops of CA glue and wood glue goes on the fence.
I spray CA Activator on the rail
When you attach the rail you have to move fast because the CA activator will start to set up the glue. I make sure both the side of the rail and fence are flush as well as the bottom which is pushed up against my fence. I used a combination square before this step to confirm that my miter gauge fence is perfectly flat and the fence is 90 degrees(perpendicular) to the rail. This part is super important.
To permanently attach the two pieces I installed four 1 1/4" screws.
This jig is going to be unique to not only the type of router I'm using but also the bit. The bit I chose was a 23/32 which is used for 3/4" plywood.
I route all the way across the jig to create the zero clearance slot.
Don't forget to make a few notes on the jig to remind yourself not only what router it's for but also the bit.
Now we can use the jig! I make a mark 5 1/4" from the bottom of this cabinet side.
I bring that line over to the edge
And then down the edge. I used my double square for this task.
The good thing about this jig is I only need 1 line! No need to measure for the second line nor will you have to measure for the base of your router as the jig will tell you everything you need to know.
Line it up with the mark and clamp it to the piece
Set the depth of the router bit and make the pass.
As you can see, perfectly straight dado that's parallel with the bottom edge and perpendicular with the edge of the cabinet.
This is a 3/4" test piece of plywood I used and it's a perfect fit. A few taps with a mallet and it goes in.