Impact drill

A power-driven impact drill for use with a drill bit having at least one peripheral groove extending parallel to a longitudinal axis of the drill bit, comprising;

• (a) a drill bit holding portion including a rotatable hollow cylindrical bit holder releasably holding therein a drill bit, at least one steel ball held on said bit holder and releasably engageable with the peripheral groove of the drill bit to couple said bit holder and the drill bit while allowing axial movement of the drill bit within a limited extent equal to the length of the peripheral groove, and a ball holder slidably fitted over said bit holder for holding said steel ball against detachment from said bit holder;
• (b) a rotational power transmitting system operatively connected with said bit holder for rotating said bit holder and the drill bit in unison;
• and
• (c) an impact power transmitting system including a spindle driven by said rotational power transmitting system and extending at a right angle to a longitudinal axis of said bit holder, a first hammer slidably mounted on said spindle for co-rotation therewith and movable along said spindle between an operative position and an inoperative position remote from said operative position, said first hammer having at least one hammering head alignable with said longitudinal axis of said bit holder when said first hammer is disposed in the operative position, a first hammer spring urging said first hammer in said operative position, a second hammer slidably mounted in said bit holder in end-to-end confrontation to said drill bit and movable to engage said hammering head for arresting rotation of said first hammer when the drill bit is forced rearward, a second hammer spring urging said second hammer in a direction away from said hammering head, and cam means acting between said spindle and said first hammer for causing said first hammer to slide along said spindle toward said inoperative position against the force of said first hammer spring when the rotation of said first hammer is arrested by said second hammer, upon detachment of said hammering head from said second hammer, said cam means permitting said first hammer to slide back to said operative position under the force of said first hammer spring while it is rotating together with said spindle, whereby said hammering head strikes said second hammer to thrust the rotating drill bit forward.