PURPOSE: To widen the bottom section of the hole of a uniform diameter formed on concrete or the like. ;CONSTITUTION: A device has a housing 12 to be inserted into a hole with a diameter to be enlarged, a pair of diameter-enlarging cutting blades 16 to be supported to be pivotally moved with the center of a pivot 14 at the tip section of the housing and to be provided with cutting blade sections 22 at respective tips (lower ends), and a driving shaft 20 to be displaced in the hole length direction and to be fitted on the housing and for transmitting a rotationally driving force to the diameter-enlarging cutting blade. The driving shaft has a pair of oblique surfaces 24 to be inclined in the mutually counter directions to be engaged with the upper ends of the respective diameter-enlarging cutting blades 16, at the tip of the driving shaft. By being moved in the tip direction, the diameter-enlarging cutting blades 16 are pivotally moved in the mutually counter directions with the center of the pivot, and the cutting blade sections 16 are mutually moved in the direction opposite to the diameter direction. The oblique surfaces of the driving shaft 20 are formed in the counter directions to be mutually adjacent over the almost full length of the same diameter along one diameter on the tip surface of the driving shaft 20.;COPYRIGHT: (C)1993,JPO&Japio
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