No. 4 Oliver expanding boring tool

No. 4 Oliver expanding boring tool, with two tommies and one spare cutters

This tool-holder is provided with an arrangement which enables the cutting tools to be moved outwards simultaneously and by an equal amount, when it is required to increase the diameter of the hole being bored.

The cutting tools are held in inclined holes in the flanges of two sleeves which are pressed together to hold the tools by means of an end nut. Their ends are chamfered and abut against the chamfered ends of two plungers whose axes are at right angles to the axes of the tools. The plungers are operated by a screwed ring and on this being rotated they press the cutting tools outwards, thereby increasing the cutting diameter. The tool-holder is arranged to be driven by a cutter from a boring bar and is locked in place longitudinally by a sunk grub screw.