Clamping device for tool holder

A clamping device for releasably holding a tool holder shank, the clamping device comprising:

• a housing having a front end, a rear end and a bore which intersects the front end and extends rearwardly therefrom, wherein a mounting portion for receiving the tool holder shank is provided at a front end of the bore;
• a drawbar slidably mounted inside the bore so as to be reciprocally moveable in the bore along a longitudinal axis thereof between an advanced releasing position and a retracted locking position;
• and
• engagement members arranged around the drawbar at a front end thereof, wherein the engagement members, under the effect of a movement of the drawbar from the advanced releasing position to the retracted locking position, are moveable from a first position, in which the engagement members allow the tool holder shank to move into and out of said mounting portion of the bore, to a second position, in which the engagement members are in locking engagement with the tool holder shank and keep it secured to the housing;
• an actuating member rotatably arranged in the bore so as to be rotatable about the longitudinal axis, wherein the actuating member is axially fixed in relation to the housing so as to be prevented from moving along the longitudinal axis;
• and
• a motion transferring mechanism arranged inside the housing, wherein the motion transferring mechanism is configured to transfer a rotary movement of the actuating member in a first rotary direction in relation to the housing into an axial movement of the drawbar from the advanced releasing position to the retracted locking position, wherein the motion transferring mechanism comprises:
• a first motion transferring element, which is fixed to or fixedly connected to the drawbar so as to be moveable along the longitudinal axis together with the drawbar and which is provided with a first pressure receiving contact surface facing towards the front end of the housing;
• and
• a second motion transferring element, which is fixed to the actuating member so as to be rotatable in relation to the housing and the drawbar together with the actuating member and which is provided with a first pressure applying contact surface facing towards the rear end of the housing for contacting the first pressure receiving contact surface, wherein the first pressure applying contact surface is configured to press the drawbar from the advanced releasing position to the retracted locking position by sliding and pressing against the first pressure receiving contact surface when the actuating member is rotated in the first rotary direction;
• and wherein at least one of said contact surfaces includes a first contact surface section and a second contact surface section arranged at different positions along an associated motion transferring element, such that, upon a movement of the actuating member in the first rotary direction, the first contact surface section is configured to slide against the other contact surface during a first phase of the movement and the second contact surface section is configured to slide against the other contact surface during a final phase of the movement, wherein the first contact surface section has a larger pitch than the second contact surface section such that the same angular displacement of the actuating member in connection with a rotation thereof in the first rotary direction in relation to the housing results in a longer axial movement of the drawbar in said first phase than in said final phase.