Patent ID: 7179024

Claim:
A tool for making an undercut in a substrate, said tool comprising: an elongated bit shaft having a cutting tip positioned at one end and a tang positioned at an opposite end, said bit shaft being rotatable about a lengthwise axis to bore an opening in said substrate with said cutting tip; a chamber located within said bit shaft and positioned between said cutting tip and said tang, said chamber having an opening providing access thereto; a cutting blade positioned within said chamber, said cutting blade being movable between a retracted position within said chamber and an extended position projecting outwardly from said bit shaft through said opening; and means for moving said cutting blade between said retracted and extended positions, said cutting blade forming said undercut when in said extended position upon rotation of said bit shaft, wherein said blade moving means comprises an axle positioned within said chamber, the chamber being defined by first and second sidewalls angularly oriented with respect to one another, said axle being substantially lengthwise aligned with and offset from the longitudinal axis of said bit shaft, said cutting blade being mounted on said axle between said sidewalls for pivoting motion into and out of said chamber, rotation of said bit shaft in a first direction causing said blade member to pivot on said axle and move into said chamber against said first sidewall upon contact between said blade and said substrate, rotation of said bit shaft in an opposite direction causing said cutting blade to pivot on said axle and move out of said chamber and into engagement with said second sidewall upon contact between said blade and said substrate.