A Trim Router Dado Jig
Some leftover 3/4” plywood for the carcass and shelves. The melamine particle board, also scrap, is to allow the router to slide more easily. Other products, like mdf, would work fine, especially if you wax it, but this was left over so I used it.
Here is the concept. The “styles” are made long enough to span both carcass sides to ensure alignment. The space between them is set by the shelf material. The “rails” can be any convenient length that will accomodate the styles and keep them square to the work. The strip sticking out is for stopped dado.
A pattern bit that is narrower than the shelf stock and set to the desired depth (1/8” in this case) will run between the styles according to the “right-hand-rule.”
To prevent the router bit “climbing,” the right-hand-rule has the thumb pointing to the side bearing surface and the fore-finger pointing in the direction the router should move.
There are myriad router bits. A pattern bit has the bearing on the top, and a flush trim bit has the bearing at the bottom. A pattern bit is used in this application, but the one pictured is too long. The shorter one shown is too short, but is what I had on hand.
Be sure the rails and styles are square. Once laid in place, it helps to trace the style onto the rail so you know about where the glue goes. I sprayed accelerator on the end of a style, put CA glue on the rail area, lined ’em up and attached. You have to work quickly with this stuff as it sets in 10 secconds. Practice first or use whatever method suits you.
Once one style is secure to one rail, insert shelf material to set spacing. Maintain parallel as best you can and glue the second style to the first rail (don’t glue the shelf material down by accident!) Then glue the styles to the other other rail. I also screwed them down.
Set the depth and rout away!
I used the Festool Domino to put the carcass together. I always mark reference sides and edges–here I did it in red Dry Erase marker so you can see it. (Dry Erase does not sink in deeply.)
In the next episode I will punch 5mm holes in the carcass sides 32mm apart to accept those little “L bracket” supports for adjustable spacing. They may not be sturdy enough for your needs, but it’s a useful exercise for me.
Posted on September 25, 2025
