| 摘要 |
An excavation tool, having a pair of insertion holes placed in the bottom surface of a device, which receives the impact force of a hammer and the rotational force of a hammer cylinder, at positions separated in a radial direction from the center of the device and symmetrical around this center as a center of rotation, also having block axles, one end of each of which is freely rotatably inserted into one of the insertion holes, and having blocks, which have a roughly semicircular shape with a diameter roughly equal to that of the device, into the lead end surfaces of which are set bits, and which have straight edge surfaces which are flat surfaces vertical with respect to the lead end surfaces, provided at the other end of the blank axles and with the straight edge surfaces in mutual opposition; in an extended diameter state of the blocks, the blocks axe moved in opposite directions along a radius of the device by rotating the blocks around the block axles, and the distance between the centers of the insertion holes provided in the bottom surface of the device and the center of this device is set at from 0.2 times the diameter of the bottom surface of the device to 0.3 times thereof.
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