Patent ID: 8544363

Claim:
A clamp device for a rotation indexing apparatus for a machine tool, the rotation indexing apparatus including a rotating shaft which is rotatably provided in a housing and to which a rotary drive target member is fixed at an end of the rotating shaft, a clamp disc which is attached to the rotating shaft such that the clamp disc is not rotatable with respect to the rotating shaft, and the clamp device which applies a pressing force to the clamp disc and clamps the clamp disc between the clamp device and a clamp surface of the housing, thereby setting the rotary drive target member to a clamped state, wherein the clamp device comprises: a cylinder element which includes a flange portion and which is detachably fixed to the housing such that an end face of the flange portion that faces the housing and an end face of the housing at a side opposite the rotary drive target member are in contact with each other, the cylinder element having a ring-shaped groove that is formed so as to be centered on an axial line of the rotating shaft; a plurality of screw members used to fix the cylinder element to the housing, the screw members being inserted through the flange portion of the cylinder element from a side of the flange portion that is opposite the housing and screwed into screw holes formed in the housing so as to open in the end face of the housing that is in contact with the flange portion of the cylinder element; a clamp element which is inserted in the ring-shaped groove in the cylinder element such that the clamp element is slidable in an axial direction of the rotating shaft, the clamp element having a pressing portion for applying a pressing force to the clamp disc in a part of an end face which faces the clamp disc in the axial direction of the rotating shaft; an engagement element which is fixed to the cylinder element at a position inside from the ring-shaped groove in the cylinder element in a radial direction of the rotating shaft and extends into an area of the ring-shaped groove, the engagement element disposed between the clamp disc and the cylinder element in an engagement direction, and a portion of the clamp element placed between the engagement element and the cylinder element; and a spring member disposed between the clamp element and the cylinder element, said spring member configured to urge the clamp element in a clamping direction, which is a direction toward the clamp disc.