Patent ID: 7658238

Claim:
An impact drill for boring a workpiece comprising: a main frame; a motor housed in the main frame; a spindle movably supported by the main frame and rotatable by the motor and movable in its axial direction; a first ratchet fixed to the spindle and having a first serrated surface including alternating projections and recesses; a second ratchet having a second serrated surface including alternating projections and recesses and in confrontation with the first serrated surface; and a first spring biasing the second ratchet toward the first ratchet, the first serrated surface being abuttable on the second serrated surface upon axial displacement of the spindle, and relative rotation between the first ratchet and the second ratchet causing alternating abutment between the projection and the recess and between the projection and the projection for reciprocating the spindle along its axis; the first spring having a spring constant which maintains the second ratchet floatingly with respect to the main frame and prevents the second ratchet and the spindle from abutting against the main frame when a force ranging from 15 to 25 kg is applied to the main frame for boring the workpiece; and wherein the first ratchet and the second ratchet are movable together in the main frame in a direction opposite to the biased direction of the second ratchet, the biased direction being given by the first spring.