Automated collar-forming drill mechanism

An automated collar-forming drill mechanism, comprising a rotatable drive shaft (1), a tool head (2) mounted on the end of the drive shaft, an actuator (3) for rotating the drive shaft, transfer means (5-9) for carrying the drive shaft (1) and the tool head (2) back and forth in a first axial direction and a second axial direction opposite to the first axial direction, said tool head (2) comprising a drill (34) for drilling a hole in a wall of a workpiece as the tool head (2) is carried in the first axial direction during a drilling operation, and collar-forming pegs (3) that extend below a rim of the hole in the workpiece to extract material encircling the hole in the wall of the workpiece for a collar as the tool head (2) is carried in the second axial direction during a collar-forming operation, wherein the transfer means includes a power unit for axial movement, said power unit comprising a double-acting piston-cylinder assembly, said piston-cylinder assembly being operable reversably in a first forward direction and a reverse second direction, said second reverse direction being actuable by means of a reversing valve (14), and a speed of motion of said piston-cylinder assembly in the first and second directions is hydraulically limited, and

• wherein said piston-cylinder assembly comprises two cylinders, each one of said two cylinders including a piston having a first side provided with a pneumatic gas, and a second side having hydraulic fluid compartments with a hydraulic fluid therein, said hydraulic fluid compartments being in flow communication with each other.