This tip is by Jodee from Inspire Woodcraft. It’s a clever and precise method for cutting flawless dados and grooves using a standard table saw blade—no dado stack or trial-and-error required.
By making a simple shim that matches your blade’s kerf, this technique offers unmatched accuracy and repeatability. It saves time, improves fit, and takes the frustration out of one of woodworking’s trickier cuts.
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Why Dados and Grooves Are Tricky
Cutting dados or grooves to fit something like a bar or plywood panel can be hit-or-miss without the right setup. Most woodworkers start with a measurement, make a pass on the saw, test the fit, and then inch the fence over for a second pass—often repeating the process several times.
Even when using calipers and marking gauges, the fit isn’t always consistent. One groove may be too tight, another too loose, and achieving repeatable cuts across multiple workpieces becomes a frustrating guessing game.
A Shim That Solves the Problem
Jodee’s approach eliminates all of that by using a shim—cut with the same blade you plan to use for the dados. This shim acts as a precise spacer between the fence and the workpiece on the second cut, making sure the groove is exactly the right width for the material you’re fitting.
The beauty of the technique is that it works regardless of what size blade you’re using. Whether it’s a thin-kerf blade or a standard full-kerf model, the shim takes out the guesswork and replaces it with precision.
Making the Shim
The process starts with two identical pieces of plywood or solid wood. By making a series of careful cuts on each piece, you create a pair that fit snugly together—like puzzle pieces.
Once cut and paired, one piece becomes the shim, and the other acts as a push block during use. Both are run through the same blade, which ensures the shim’s width matches the kerf exactly.
The material you use for the shim should have a clean, jointed edge to run flush against the fence. Baltic birch plywood or straight-grained hardwood works well. A long enough shim will also ensure stability and smoother feeding when it’s used.
Cutting Dados and Grooves with the Shim
Here’s how the shim is used during the dado process:
Step 1: Place the workpiece (like an aluminum bar or a shelf panel) between the saw fence and your stock. Make the first cut with this setup, establishing one edge of the dado.
Step 2: Remove the material you’re fitting and replace it with the shim. The shim offsets the fence by the exact width of the blade.
Step 3: Make the second cut. This defines the other edge of the groove with precision.
Step 4: Remove the waste in the middle. This gives you a groove that fits the original material snugly and cleanly.
For wider grooves, repeat the center-clearing process with additional passes. The key is that the shim keeps every pair of cuts consistent and accurately spaced.
Making Adjustments for Glue or Clearance
If you want a little extra room for glue, Jodee recommends applying a strip of masking tape to the material before the first cut. This small increase in width builds in just enough space for glue squeeze-out and easier assembly.
If a groove ends up too loose, you can also wrap the shim itself in masking tape to tighten the fit. These small tweaks allow you to fine-tune the results without adjusting the fence or re-cutting the shim.
Improving Cut Quality
Another tip is to raise the saw blade higher than normal when making these cuts. A taller blade makes a cleaner vertical edge, reducing the slight slope or “ramp” effect you get when cutting with a low blade height.
Jodee has a quick video on setting blade height that pairs well with this dado technique. It’s a useful addition if you’re aiming for crisp, square joinery across multiple parts.
Safety Matters
While raising the blade may seem like a safety concern, Jodee points out that this method is no more dangerous than a regular table saw cut. The material and shim ride firmly against the fence, and you’re always pushing with control and distance.
He also suggests starting with wider stock when making the shim, so your hands stay well clear of the blade. Using the second piece as a push stick is another smart move that keeps things safe throughout the process.
Why This Technique Works
If you try to cut both sides of a groove without a shim, you’ll accidentally make it too wide. That’s because the blade removes material on both passes without shifting the fence. The shim fixes that by perfectly accounting for the blade’s kerf width between cuts.
And because the shim is made with the same blade, you don’t have to measure anything. No calipers, no adjusting the fence back and forth—just a repeatable, fast system that gets it right the first time.
A Better Way to Cut Dados and Grooves
This shim technique is especially helpful for projects with repeated dados or for fitting unusual materials like metal bars, splines, or custom panels. It’s accurate, adaptable, and easy to store with your other shop jigs.
Jodee has also used variations of this method for other joinery tasks, including half-laps and miter splines. If you’re looking to improve your table saw accuracy without investing in new blades or tools, this is a tip worth trying.
Support Jodee by visiting his online store here: https://inspirewoodcraft.com/collections/all.