Every woodworker makes the occasional mistake. Some are easy to fix, while others require a little creativity.
One challenge that can be especially frustrating is discovering that a hole you've already cut is too small. Simply switching to a larger drill bit or hole saw isn't always an option. Without the original center to guide the bit, getting the new hole positioned accurately can be difficult.
Fortunately, there's a simple solution using a handheld router, a rabbeting bit, and a pattern bit.
The trick is to use the existing hole as a guide so the enlarged opening stays centered in exactly the same location.
Start with a Rabbeting Bit
In this example, the existing hole needed to be enlarged by 1/4" in diameter.
Instead of trying to center a larger bit over the opening, start by installing a bearing-guided rabbeting bit in your handheld router.
Set the bit to cut a rabbet 1/8" deep.
The bearing follows the lower portion of the existing hole as you rout around its circumference, creating a larger-diameter recess at the top of the opening.
The important detail is that the original hole guides the cut. There's no need to locate its center again.
The rabbeting bit's bearing and cutting diameter determine how much larger the opening becomes.
Switch to a Pattern Bit
Once the rabbet is complete, switch to a bearing-guided pattern bit.
The newly routed rabbet provides the reference for the second cut.
Position the bit so its bearing rides against the wall of the enlarged recess. Then rout away the remaining waste below the rabbet.
Because the bearing follows the first cut, the pattern bit transfers the new diameter through the rest of the hole.
The result is a clean, accurately enlarged opening that remains centered on the original hole.
Woodsmith Tip: Match the Bits to the Job. The difference between the rabbeting bit's cutting diameter and its bearing diameter determines how much material is removed around the hole. For example, increasing a hole's diameter by 1/4" requires removing 1/8" from the radius all the way around. Choose a rabbeting bit with the appropriate offset, and make sure the pattern bit's bearing can follow the new rabbet without cutting into the original reference surface.
A Simple Fix for an Undersized Hole
This technique is especially useful when the location of the hole is critical and you don't want to risk shifting its center.
Instead of relying on a new layout or trying to hold a larger drill bit in position, you let the existing hole guide both routing operations.
Just secure the workpiece firmly, support the router base, and use appropriate routing depths for the material and bit.
With two common router bits and a little careful setup, an undersized hole becomes an easy problem to correct.
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