Patent ID: 7331742

Claim:
A spindle unit of a machine tool for mounting a tool or a workpiece pallet on a forward end of a spindle, comprising: a spindle supported by a housing so as be rotatable; a clamping device provided in a hollow portion of the spindle and including a draw bar for engaging the tool or the workpiece pallet and an elastic member for pulling the draw bar rearward; an unclamping device provided at a rear portion of the spindle for pushing the draw bar forward to thereby release the tool or the workpiece pallet; an oil pool chamber formed in the hollow portion of the spindle having a closed chamber structure and including bearing portions for supporting the draw bar on both sides configured so that the draw bar is movable forward and rearward, said bearing portions having substantially the same size so that the volume of the oil pool chamber does not change when the draw bar is moved forward and rearward; and at least two passages having inner threads and formed in the spindle communicating between an outside of the spindle and the oil pool chamber, each of said passages being formed at the forward end of the spindle.