This tip is by Jodee from Inspire Woodcraft. It’s a practical solution to one of the most frustrating problems in woodworking: routing a dado that perfectly matches your material—without needing a jig or a custom-sized bit.
Instead of buying a new bit for every application or building a complex jig, Jodee uses a simple spacer made from scrap material to dial in precise cuts. It’s an elegant solution that makes your router more versatile and your workflow more efficient.
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The Problem: Bit Sizes vs. Actual Material Dimensions
Most router bits are designed around nominal sizes—1/2″, 3/4″, etc.—but real materials often measure slightly over or under those values. Baltic birch plywood, for instance, is a common material that’s rarely a perfect match to bit sizes.
When the fit isn’t tight enough, pieces can rattle. When it’s too tight, parts don’t go together at all. Jodee’s method avoids this issue entirely by letting you create a perfect-fit dado or recess every time using a reusable spacer.
How the Spacer Method Works
The key to this trick is using an offcut made from the same material you want to recess. This offcut becomes a custom spacer that compensates for the difference between your router bit and the material’s actual thickness.
By shifting the router’s position during a second pass, the spacer lets you widen the dado precisely to fit the material. There’s no guesswork, no fancy jigs, and no need for an expensive set of micro-sized bits.
Step-by-Step Overview
The setup begins by securing two pieces of equal-thickness material to your bench. These act as guides and supports—one under the workpiece, one under the router base—with a gap between them for the bit to spin freely.
Jodee places a square against the side of the router as a reference and makes a first pass to square the edge of the offcut. Then he removes the offcut, makes a second pass through the gap, and produces a shim that’s exactly the size of the difference between the bit and the material thickness.
This spacer becomes a tool for future routing. A small nub or “ramp” on the end helps it hook into place between the router base and your square or straightedge, allowing you to repeat the process with extreme accuracy.
Using the Spacer in a Dado Cut
With the shim complete, it’s time to put it to work. Set your straightedge or square where you want the dado and clamp it securely.
Make a first pass along the guide with your router and bit. Then insert the spacer between the router base and the guide and make a second pass. That small offset—provided by the shim—widens the dado to match the exact thickness of your material.
Because the shim is made from the same stock, the fit is as accurate as it gets. And since the router rides along the same guide, you don’t need to measure and mark both edges of the dado.
Why It’s So Effective
This trick works for a few key reasons:
- The shim is made from your actual work material, so the fit is always accurate.
- It removes the need for multiple jigs cluttering your shop.
- It saves money—no specialty router bits required.
- It’s fast and repeatable across multiple workpieces.
- You only need to mark one line instead of measuring both edges of every dado.
If the fit is ever slightly off, a single layer of masking tape on the shim can add just enough thickness to get it right. That kind of flexibility makes this trick useful in all sorts of joinery applications.
Pro Tips for Best Results
Jodee offers a few smart reminders to make sure this technique works smoothly:
Use quality plywood for the shim to avoid flexing or crumbling during routing.
Keep the ramp or nub on the end intact—this helps it seat securely between your router and guide.
Sand the shim lightly if needed, but don’t alter the thickness.
Use a square or straightedge that’s easy to clamp and align.
Take multiple passes with your router for cleaner results on harder materials.
A Smarter Approach to Shop Efficiency
This is more than just a router tip—it’s a mindset. Instead of spending more money or space on tools and jigs, Jodee shows how a simple idea and a scrap of wood can improve your results and speed up your work.
It’s especially helpful if you work with plywood often or need repeatable fits across multiple pieces. By creating a reusable tool that adapts to your materials, you gain control over one of the most frustrating parts of joinery.
Support Jodee by visiting his online store here: https://inspirewoodcraft.com/collections/all.