In a boring machine, the boring sleeve refers to the cylindrical part protruding towards the direction of the rotation axis inside the rotating spindle. Tool holder is mounted at the end of the boring sleeve. The protruding axis is usually controlled by the W-axis.
The boring sleeve is distinguished from the quill or the ram of the spindle, which includes spindle itself. The boring sleeve is cylindrical, and the ram is the shape of four sided pillar.