This tip and technique video was created by Jodee from Inspire Woodcraft.
In it, he explores whether using a drill bit as a shim substitute when cutting dados on the table saw can actually deliver accurate results.
It’s a long-debated trick among woodworkers—substituting a drill bit for a precise blade-width shim.
Jodee walks through a real-world test to see if this popular shortcut holds up when precision matters.
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Why Shims Matter for Dados
When cutting joinery like dados, grooves, or half laps, precision is critical. A mismatch of just a few thousandths of an inch can lead to loose joints or structural issues.
To avoid this, many woodworkers rely on custom blade-width shims. These help offset the blade’s kerf when making multiple passes, ensuring that the cut fits the material exactly.
But not everyone has pre-made shims on hand, which leads to the question: can a drill bit of the same width serve the same purpose?
Testing the Shortcut
Jodee sets out to answer that question by running a side-by-side test. Using a crosscut sled fitted with zero-clearance tape for better accuracy, he selects a Forrest Woodworker II blade—known for producing flat-bottom dados.
To test the drill bit method, he uses two different eighth-inch bits: one standard twist bit and one brad point bit.
Each bit is measured carefully, though neither perfectly matches the blade’s kerf. For comparison, he also uses a custom shim that closely matches the blade’s actual cut width.
The Cutting Setup
For each test cut, a stop block is clamped to the sled to ensure consistency.
Jodee positions the material, makes an initial cut, and then uses either a drill bit or the shim to slightly shift the position for the second cut.
The idea is that by adding the width of the drill bit or shim between the workpiece and the stop block, the resulting cut will be exactly as wide as the material meant to fit inside the dado.
This technique relies on the assumption that the added spacing compensates precisely for the blade’s width.
Results from the Test
After making all three dado cuts—one with the twist bit, one with the brad point bit, and one with the shim—Jodee examines the fit of the mating piece.
The shim-cut dado fits snugly with little to no play. However, both drill-bit cuts leave noticeable gaps. Using a set of feeler gauges, Jodee finds that the drill-bit-based dados are between 0.008 and 0.010 inches too wide.
Though this may seem like a minor difference, it can be significant depending on the type of joint being made.
In joinery where precision is critical, even slight play can lead to misalignment, glue line gaps, or weakened joints.
Why the Difference Happens
One of the key takeaways from the video is that actual cutting results rarely match theoretical measurements.
Even if the blade and bit are the same nominal width, several variables can throw off the outcome.
Jodee points out that blade geometry, material deflection, and the way a blade moves through the cut all affect the final kerf width. A shim made specifically to match the blade’s real-world cutting behavior will almost always produce better results than a measurement-based substitute.
When the Trick Might Work
That said, the drill bit trick isn’t entirely useless. In cases where ultra-tight tolerances aren’t necessary—like cutting slots for decorative inlays or quick shop jigs—it may be good enough.
For woodworkers who don’t yet have a set of shims or need a fast workaround in a less critical application, the method could still serve as a temporary fix.
But for structural joinery, miter splines, or precision cabinetry, it’s better to build or buy accurate blade-width spacers.
Lessons from the Experiment
This experiment highlights how even small assumptions in woodworking can lead to imperfect results.
Measuring isn’t always enough—real-world testing is often the only way to know whether a technique will deliver the fit you need.
By putting a common shop myth to the test, Jodee shows that taking a little extra time to create proper shims can pay off in the long run.
His practical approach helps other woodworkers avoid relying on shortcuts that may not hold up when precision matters most.
A Thoughtful Take on Shop Tips
Like many of his videos, this one is part of Jodee’s broader effort to question assumptions and improve shop techniques.
Rather than promoting quick hacks, he emphasizes accurate, repeatable results through careful experimentation.
This mindset encourages woodworkers to evaluate the tools and tricks they use, and to choose methods that align with their goals—whether that’s speed, cost, or long-term reliability.
Support Jodee by visiting his online store here: https://inspirewoodcraft.com/collections/all.