Patent ID: 7758288

Claim:
An expanded hole drilling device comprising a table having a fixing element for detachably fixing a bored workpiece; and a hole drilling part having a drill grasping part to which a drill capable of drilling a hole having a diameter larger than that of a bored hole is attached, characterized in that the device has a drill holder attached to the drill grasping part in place of the drill; and a centering attachment having a diameter larger than that of the drill holder, the centering attachment being attached to the free end part of the drill holder on the side opposite to the side on which the drill holder is attached to the drill grasping part, the free end part of the drill holder is formed into a conical shape having the same axis line as that of the drill at the time when being attached to the drill grasping part, and a hole part in which the drill is insertably fitted is formed in the free end part, the hole part having the same axis line as that of the conical shape, and for the centering attachment, in the end part on the side of being attached to the free end part of the drill holder, there are formed a taper-shaped opening in which the free end part of the drill holder is insertably fitted, the taper-shaped opening having the same axis line as that of the drill holder, and a hole part that communicates with the taper-shaped opening and has a space capable of accommodating the exposed part of the drill attached to the drill holder, and also the other end part is formed into a conical shape having the same axis line as that of the hole part.