Dado sizing for finished plywood

[Stephen McBride]

Stephen, Stephen, Stephen …..

You’re showing up the side. This confluence of .events gives you broad plausibility for new tools

Don’t laugh in the face of The Tool Gods.

I’m still in the early phases of getting tools. Just had my first project where all I had to buy was lumber a few weeks ago and she’s beginning to see the light of actually having the tools.

Router and bits are gonna be the buy for this one

[Mike Wilkins]

Rick Potter hit the nail on the head. If you make an adjustable routing jig you can size the dadoes to the exact thickness of the plywood. Use a 1/2" bit with bearing-run it up the left side and back down the right side. Just did it with hardwood and the fit was perfect.
Or you can just jump ahead of the line and get the Woodpeckers dado jig if your wallet can handle it.

[Bob Cooper]

For me it’s far easier to cut a rabbet on the shelf (slightly undersized) and a dado on the side. That way the fir does not have to be exact

[Rich Engelhardt]

Look on YouTube for videos of simple router guides to make dado's. It's easy to make one for the specific ply you are using, or go fancy and make an adjustable model. These jigs use a smaller bit (like 1/2"), and you go up one side and down the other to get the exact size dado.

There are dozens of examples there.

This right here...
As a matter of fact - way back in 2007, I was searching for this exact jig and one of the links was to Sawmill Creek.
The funny thing is - I still haven't gotten around to making the dumb thing!

A simple search for "dado jig" on Youtube will provide a bunch of different jigs.


A "kerfmaker" is another method that can be employed.

I forgot to add - - I'd size the jig to use a 3/8" bit instead of a 1/2" bit. That way it can be used for 1/2" material also.

[Kevin Jenness]

For me it’s far easier to cut a rabbet on the shelf (slightly undersized) and a dado on the side. That way the fir does not have to be exact

If you are going to make a dado and rabbet (t&g) why not make it fit correctly? The joint will be stronger and the shelf located accurately without visible gaps. The key is to gauge the tongue thickness off the uncut face, thus avoiding inaccuracy caused by varying sheet thickness. This can be done on a router table with a rabbeting bit above the tongue or on a shaper, but not with a dado blade in a tablesaw (unless the shelf is stood on edge).

[Rick Potter]

Welcome to the wonderful world of woodworking. Lots of opinions, and all are viable.

Just wondering if you have a table saw yet? That is often the best tool for dado's, but since you referenced router bits, I didn't mention it in my previous post.

If you don't yet have one, be sure to get one that takes a dado stack.

[Thomas McCurnin]

+1 for Rick's comment.

A table saw is easier and more accurate to make dados, because the blades can be shimmed with thin shims for a perfect fit. There are plastic shims available as well to supplement whatever shims were provided with the dado set. I would also make test cuts with the plywood to insure a perfect fit.