Patent ID: 7931131

Claim:
A rotational resistance applying device in a main shaft driving device for a machine tool, the main shaft driving device rotationally driving a main shaft rotatably supported by a frame and comprising a clamping device that causes a pressing force to act upon the main shaft for applying rotational resistance that prevents its rotation so as to maintain its angular position, the rotational resistance applying device comprising: a pressing member provided adjacent to the frame, at least part of the pressing member being displaceable towards the main shaft, the pressing member having a first surface; a pressing force applying device that applies a pressing force to the pressing member to displace the at least part of the pressing member towards the main shaft, so that the pressing force acts upon the main shaft or a member that rotates together with the main shaft, the main shaft or the member that rotates together with the main shaft serving as a press member that is pressed and that has a second surface; and a resiliently deformable rolling member provided between and the first surface and the second surface, the first surface causing the pressing force to act upon the press member, the second surface facing the first surface, causing a pressing force to act upon the main shaft for applying rotational resistance that allows its rotation.