To drill slits smoothly and efficiently while giving uniform revolving torque and striking force to all juxtaposed rods in a drilling machine, in which a plurality of the rods, in which drilling bits are protruded at front ends, are juxtaposed and which drills the slits to a bedrock by striking a blow while rotating these rods.
Rods 1A, in which small-diametral drilling bits 2 and large- diametral drilling bits 3A are installed integrally at front ends at small intervals in the longitudinal direction, and rods 1B, in which the small-diametral drilling bits 2 and large-diametral drilling bits 3B continued at the rear ends of the small-diametral drilling bits 2 are mounted at front ends, are juxtaposed alternately under the state, in which all small-diametral drilling bits 2 are arranged on the same plane. Small pits are drilled and excavated to a bedrock by the small-diametral drilling bits 2 of the rods 1A, 1B while large-diametral pits obtained by expanding each small-diametral pit by the succeeding large- diametral drilling bits 3A, 3B are excavated, and slits, in which the adjacent large-diametral pits are communicated mutually, are excavated.
TSUJI IKUO
HAGIMORI KENJI
YASUI KEISUKE
