Creating dados for shelves is a pretty common task when making something like a bookcase. Using a router is notably easier than using a table saw with a dado blade, but it does come with its own unique problem. That is, the thickness of the shelf is very likely going to be different than the thickness of your router bit. That’s because most shelves are made from plywood, which runs small.

This article shows how to make a custom router template using scrap pieces that will produce perfectly sized dados every time.

Video

What You Need

• Router
• Straight cut pattern bit that’s skinnier than your dado width
• Flat piece of plywood or MDF that’s wide enough to support your router
• Long piece of wood to act as a perpendicular fence

The pattern bit is the key, here, and it must be smaller than the dado. That is, if your dado is almost 3/4″, then the bit should be 1/2″ or similar. In my example here, I’m using a bit specially made for dados, which has a flat bottom.

The flat piece is plywood and just wide enough to support the router and tall enough to cover the shelf support plus the upper and lower fences. My shelf support is 8-1/4″ wide and so the flat piece is somewhere around 10″ long. I made sure the scrap had at least one straight side so I could guarantee a straight rip for the surface that the pattern bit will be riding on.

The fences are made up of a spare piece of pine. The part that matter is for it to have one straight edge to ride against the shelf support. I’m not going to use pine anymore for a fence since it moves too much — a scrap piece of MDF or plywood would work much better.

Here’s the four pieces all ripped to size:

Assembly

The first step is the most important — attach one side of the flat piece to one of the fences ensuring that it is completely perpendicular (90 degrees). I do this by first pressing the fence piece up against the shelf support, then attaching the flat piece to this fence with a single screw in the corner. That allows the piece to still pivot. Next, put a speed square in place and flush the flat piece up against it. Drive in a second screw to secure the flat piece in place. That will ensure that the flat piece and one fence are at 90 degrees.

Next, attach the upper fence to the same piece. It should automatically be parallel to the first fence and square to the flat piece.

The third step is to take a sample of the shelf and press it up against the attached flat piece. It’s critical to use a sample of the actual shelf since this’ll be creating a template that is custom to exactly that thickness. Next, sandwich the self sample using the final flat piece. Attach that piece to both fences.

That’s it. You know have a custom dado template that will create perfect fit dados for your specific shelves on your specific shelf support piece.

Usage

Place the template where you want a dado cut with one of the inside edges being flush with the bottom or top of the dado. The template should fit pretty tightly if it was made like described above. If there is a little play, then feel free to clamp it down.

Insert your pattern bit into your router and adjust the depth to be the thickness of the template plus the depth of the cut. In my case, my template was roughly 3/4″ thick and I wanted to go 3/8″ deep, so I set it to a depth 1-1/8″. The temple thickness isn’t measured though. Instead, I zeroed the depth gauge out using the template itself and just measured the desired 3/8″ depth.

Route up one side of the template and then down the other side, making sure that the pattern bearing rides on the flat piece both ways. I found that doing a couple shallow cuts makes a cleaner cut, in addition to producing a more manageable amount of dust.

When you’re done, you’ll have a dado that perfectly fits your shelf!

Final Thoughts

This is a quick enough build to make it worth doing potentially even if you’re only cutting one dado. It really comes into its own when having to create multiple dados, though. It’s one downside is that it’s usable only for a specific shelf thickness and a specific shelf support width. If either dimension changes, then you’ll need to create a new template.

A more flexible solution is to create an adjustable template that is re-usable for multiple projects. That’s a bit more work. I’ll be creating one of those in a future project.