Collet chuck provided with a driven movable member which can be driven hydraulically in two opposite directions for operating a collet

A collet chuck comprising:

• a tubular body having a front end and a rear end;
• a rotating shaft assembly journalled within said tubular body, and having a frustoconical recess;
• a belt pulley sleeved fixedly on said rotating shaft assembly;
• a collet disposed operably within said frustoconical recess in said rotating shaft assembly and adapted to hold a rod-shaped workpiece therewithin;
• and
• a movable member mounted axially and movably within said tubular body and movable within said tubular body in a selected one of a tightening direction and a loosening direction;
• said tubular body further having
• a front oil chamber formed in said tubular body and located immediately in front of said movable member,
• a rear oil chamber formed in said tubular body and located immediately behind said movable member,
• a first oil passage formed in said tubular body and in fluid communication with said front oil chamber so that hydraulic oil can be fed to said front oil chamber therethrough, thereby moving said movable member rearward within said tubular body, and
• a second oil passage formed in said tubular body and in fluid communication with said rear oil chamber so that hydraulic oil can be fed to said rear oil chamber therethrough, thereby moving said movable member forward within said tubular body;
• wherein movement of said movable member in said tightening direction is one of forward and rearward movements of said movable member within said tubular body and results in further movement of said collet into said frustoconical recess in said rotating shaft assembly for compressing said collet, and wherein movement of said movable member in said loosening direction is the other one of said forward and rearward movements of said movable member and results in movement of said collet away from said frustoconical recess in said rotating shaft assembly so as to be adapted to release the workpiece from said collet.