The magic of dado blades is you can adjust them for virtually any cutting width you like.

But what’s the best way to set the precise thickness you need?

An obvious one is to use the guide that comes with your dado stack.

It tells you a precise number of chippers, spacers, and shims to place between the outer blades to add up to a specific measurement.

But there are two potential problems with this:

1. You might lose the thickness guide (tape it to your forehead to avoid this).
   
   
2. Even if you follow the guide, the final thickness might not be a perfect fit for your joinery. Sawdust or grime between shims can add extra thickness — or your workpiece might not be the exact measurement you think it is.

As is often the case in woodworking, I find the best solution is to reference reality.

And here’s how to do that while setting your dado stack thickness.

(Need a dado blade set? Check out our collection here).

Start by stacking the outside blades of your dado set on a flat surface.

I like to do this on a flat piece of plywood so I don’t damage the teeth. If you’re careful, you could also set them on the cast iron table of your table saw.

Make sure none of the teeth from one blade are touching the teeth of the other.

You want the main bodies of the two blades to be flat against each other — otherwise, your calculations will be off.

Now grab the mating workpiece and set it next to the blades.

What’s the mating workpiece?

It’s the board that will fit into whatever groove, dado, or rabbet you end up cutting with the dado set.

Set it flat on its side next to the blades so you can compare their thicknesses.

Now it’s just a game of stacky-matchy.

Start stacking chippers on the outside dado blades.

Again, make sure none of the teeth are touching each other so they stack flat.

You’re looking to see how the teeth on the top chipper of the stack compare to the thickness of your workpiece.

Keep adding chippers until you can’t add another without its teeth being higher than the workpiece.

Now it’s time to fine tune.

Now slide some spacers or shims between the chippers to reach the perfect thickness.

But here’s a common mistake to avoid:

In most cases, you don’t actually want the dado blade to be the exact thickness of your workpiece — but instead, just a hair thicker.

The stack can compress slightly when you tighten it on the table saw arbor. And the result is a cut too tight for your workpiece to fit into.

(A common misconception in woodworking is that joinery needs to be super tight before adding glue. Ideally, you should be able to seat joinery with just your hands — but it should still hold together).

You want to just barely feel the top of the tooth with your finger or a ruler compared to the workpiece.

Once it’s there, you’re ready to place the dado stack on your arbor.

Before cutting your final joinery, make a test cut in a piece of scrap.

Then see how your workpiece fits into it.

Again, you should be able to seat the workpiece by hand without it wobbling in place.

If the joint’s too tight, add an extra shim to the dado stack. Vise versa if it’s too loose.

Once the test cut fits right, you can start moving forward with your project.

Referencing reality is often the best approach for accurate woodworking — and this dado blade set up technique is a perfect example.

Want to learn all the joinery styles dado blades can be used for? Read this.

What’s your preferred method for setting up dado stacks? Let us know in the comments below!

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