Patent ID: 7275899

Claim:
A machining apparatus comprising: a spindle; means for supplying a coolant to a machined portion of a workpiece in contact with a machining tool fitted to the spindle, via coolant supply passage formed in the spindle, while machining the workpiece; and a clamp device comprising at least one fluid pressure cylinder device to which the coolant is supplied, and a clamp member that clamps the workpiece and that is actuated by the fluid pressure cylinder device, responsive to the supply of coolant to the fluid pressure cylinder device; and wherein the fluid pressure cylinder device comprises a cylinder, a double-acting piston that divides the interior of the cylinder into a clamping pressure chamber and an unclamping pressure chamber, and a piston rod extending from the piston, whereby the clamp member is actuated to clamp the workpiece by supply of coolant to the clamping pressure chamber, and the clamp member is actuated to release the workpiece by supply of coolant to the unclamping pressure chamber.