Air-operated self-propelling rotary-percussive downhole drill

The drill has a housing receiving therein a reciprocating striker, effecting percussive action upon the tool for breaking the rock at the face of the hole, mounted at the forward part of the housing, and upon the housing itself for propelling the drill in the hole. The housing also receives therein a mechanism for rotating the tool, including a self-controlled coupling provided with a movable sleeve and a stationary sleeve and adapted to transmit a torque to the tool in only one direction of rotation. The drill is provided with a device preventing a rearward motion of the housing and its rotation during a drilling operation. The drill is characterized by having a return device for retracting the tool from the face after it has been struck by the striker. The return device includes a piston mounted on the tail portion of the tool and mounted intermediate the striker and the forward bottom of the housing, a piston space defined between the piston and the forward bottom of the housing and a resilient member accommodated in this space and cooperating with the piston.