A dado is a very common type of joinery in woodworking. It's super simple to make and the joint is very strong. There are many ways to make this type of joint and the easiest would be to use a dado stack. But the thing about dado stacks is it's not available in every country, some table saws don't allow you to install one, and the stack itself can be pretty expensive. Another way to make dados is to use a router, which is what this jig is for. There are router bits that are made specifically for certain plywood sizes, but that means more cost in buying router bits and maintaining them. This jig will allow you to make perfect dados no matter what thickness of the material you are using. It also will allow you to make rabbets, and half-lap or tapered half-laps joints.

Supplies

The supplies you will need are:

(1) 3/4" plywood sheet (you probably only need half a sheet.)

(1) 1/2" plywood sheet (you can use half of a sheet or less.)

(6) 5/16x8 threaded start knobs (I CNC my own but you can buy these)https://amzn.to/3dGFped

(6) 5/16x8x2.5 T-bolt https://amzn.to/35XqGcd

(6) 5/16 Nuts (if you're making your own knobs)https://amzn.to/2WNJmHm

(6) Washer https://amzn.to/3dYUFDJ

Wood Glue

Tools:

Table saw (Circular saw or jigsaw with a straight edge if you don't have a table saw)

Drill press or Power drill

Forstner bit or drill bits

Patterning Bit https://amzn.to/2X0q4ic

Step 1: Breaking Down the Plywood Sheets

The first thing you will need to do is to break down the plywood into strips. There is some variation in these dimensions based on how long you want to make your dados. For me the dimensions I used are the following:

Main guides : 24"x3.5"

Top fence piece : 12"x3.5"

Bottom fence piece : 12"x3.5"

Optional center guide : 24"x2"

If you're following the plans laid out in the YouTube video, you can ripped the plywood into 3.5" strips and that take care of any measurements as far as the widths are concerned. The length will vary, again, based on your needs. I'm using my table saw to cut all these pieces. If you don't have a table saw, you can use a circular saw with a straight edge to make these cuts.

Once the widths are cut, you can then cut the piece to the appropriate lengths. I used a crosscut sled on my table saw for this, but you can use a miter saw or circular saw with a straight edge if you have one.

In the end you should have a total of 7 pieces including the option center guide.

Step 2: Creating the T-Bolt Slots

For this portion, you'll have make sure you're marking and cutting the correct dimension for on the correct fence piece. The 1/2" thick plywood fence piece will have a slot created for the t-bolt head while the 3/4" thick plywood fence piece will have a slot for the t-bolt shaft.

Lets start with the 3/4" thick fence piece

First I located center slot for t-bolt shaft, which in my case was 1" away from the edge. From there, I measure the width of my bolt and marked a line for both sides of the shaft. I stopped the marks just shy of 1" from the ends of the piece.

Now lets mark the 1/2" thick fence piece

The same process for marking the shaft applies to the t-bolt head, but the dimensions will differ since the t-bolt head is slightly larger than the shaft. I marked the center for the slot 1" from the edge. From there I centered the bolt head and marked the lines for both sides of the head. I stop the marks 1/2" shy from the ends of the piece.

Slotting the 3/4" thick rails pieces

First I located center slot for t-bolt shaft, which in my case was 1" away from the edge. This offset is to allow for the router base to freely move without hitting into the knobs. Same thing with the previous process, I marked the left and right side of my bolts and marked the line stopping shy of the ends by 1".

Making the cuts

To make the cut, I first used a drill press to create a starting whole at both ends. If you don't have a drill press, you can always use a power drill with a forstner bit or a drill bit. From there I use my table saw to complete the slot but slowly raisin up the blade and carefully pushing the piece through. I stopped the cut before the blade exits the piece or before it passes my marked lines. If you're not comfortable with this, you can use a jig saw, which i did to complete the slot cuts.

Gluing the 1/2" and 3/4" fence pieces

Once the slots are cut, take the 1/2" plywood fence piece and the 3/4" plywood fence piece and glue them together. The 1/2" piece should sit at the bottom and the 3/4" piece should sit on top.. The 1/2" piece will be where the t-bolt head rides so that slot will be wider.

Step 3: Making the Knobs

You can skit this step if you're going to buy the knobs.

You can find some CNC files online for these knobs. I modeled them myself. This process is quite simple since the CNC did most of the work. Once the pieces were cut out, I use epoxy to set in my 5/16 nuts and let it dry over night. Once the epoxy cures the nut will stay nice a secure in that pocket.

Step 4: Sanding

Now that all the pieces are cut and the epoxy is cured, I sanded everything down with 120 grit sand paper. You can keep the plywood raw if you would like or add a coat of wax to seal things off. With sanding plywood, you don't want to be too aggressive. By aggressively sanding you could remove the top layer and expose the bottom ply layers. It's not a big deal since it's really all aesthetics.

Step 5: Assembly

Once everything has been sanded, the jig can be assembled. First, insert the t-bolt through the fence. The head should sit inside the slot in the 1/2" plywood bottom piece of your fence and poke through the top of the 3/4" plywood piece. Next, place the 3/4" guide piece through the bolts that is sticking out of the fence. This guide acts as a reference for your router patterning bit. Finally you can use the knobs to tighten everything in place. What you should see in the end is 2 fence piece that connects two guide rails.