Patent ID: 7717770

Claim:
An apparatus for grinding both inside surfaces of a concrete joint simultaneously, comprising: a proximal grinding wheel having a rotational axis orthogonally intersecting a center thereof, proximal and distal sides, at least one peripheral edge connecting the proximal and distal sides, at least one grinding implement fixed with the distal side proximate the peripheral edge thereof, and an external drive shaft co-aligned with the rotational axis and fixed at a distal end thereof to the center of the proximal grinding wheel; a distal grinding wheel having the rotational axis orthogonally intersecting a center thereof, proximal and distal sides, at least one peripheral edge connecting the proximal and distal sides, at least one grinding implement fixed with the distal side proximate the peripheral edge thereof, and an internal drive shaft co-aligned with the rotational axis, fixed at least partially within the external drive shaft, and fixed at a distal end thereof to the center of the distal grinding wheel; a means for selectively moving the proximal and distal grinding wheels apart by telescoping the internal and external drive shafts; a source of rotational kinetic energy; and a means for selectively coupling the source of rotational kinetic energy to each drive shaft; whereby with the grinding wheels coupled to the source of rotational kinetic energy to rotate the grinding wheels, and with the grind wheels moved close enough together so that an arc of both grinding wheels may be placed into the concrete joint, the grinding wheels may be moved apart from each other until the grinding implements of each wheel contact the inside surfaces of the concrete joint to grind same.