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How does an expansive bit work?

Shop for Expansive bits

Image showing an expansive bit boring a hole and leaving noticeable spur marks around the perimeter An expansive bit works in a very similar way to a wood boring auger in that the outer edge of the bore hole is cut by a spur, and waste material is cleared by two sharp cutting lips.
A guide screw on an expansive bit Once the bit starts turning, the thread on the guide screw bites into the wood and starts to draw the tool downwards.
Image of a DIYer boring a hole with an expansive bit which works by scooping out wood chips using its primary and outrigger lips The primary spur (the one nearest to the guide screw) contacts the wood first, and the primary lip starts to bore a small hole. Next to engage is the outrigger cutter spur, followed by the cutter lip, which widens the hole to the diameter set by the user.
Diagram to show the order in which the lips on an expansive bit engage with a wooden workpiece In essence, the expansive bit’s lips cut two holes. The first acts as a pilot and keeps the bit level. The second takes care of drilling out the actual hole