Abstract: A cutting tool holder unit is composed of a cutting tool holder adapted to detachably mount a cutting tool thereon, and a front cover of a flange shape slidably fitted into a side of the cutting took holder mounted on a multi-spindle head. A groove formed on the inner circumferential surface of the front cover is slidably fitted into a groove formed on the cutting tool holder to form a cutting oil circulating channel and a cutting oil injection port is opened at an upstream position of a cutting tool mounting section relative to the direction of rotation of the cutting tool holder.

Abstract: A cutting tool holder unit is composed of a cutting tool holder adapted to detachably mount a cutting tool thereon, and a front cover of a flange shape slidably fitted into a side of the cutting took holder mounted on a multi-spindle head. A groove formed on the inner circumferential surface of the front cover is slidably fitted into a groove formed on the cutting tool holder to form a cutting oil circulating channel and a cutting oil injection port is opened at an upstream position of a cutting tool mounting section relative to the direction of rotation of the cutting tool holder.

Abstract: A boring apparatus and process comprising suspending a boring bar for boring a hole in a workpiece for universal pivotal movement in all directions. Then, the workpiece is brought below the boring bar with the axis of the hole being vertical. Thereafter, the boring bar is lowered and eccentrically passed through the hole in the workpiece and slidably and rotatably supported at least at two points thereof axially spaced apart. Then, the boring is effected by the rotation and axial relative movement of the boring bar with respect to the workpiece, with the axis of the boring bar aligned with the axis of the workpiece.