Spindle head unit of a machining center

Claim 1

In a spindle head unit of a machining center of the type having a tool magazine for storing tools therein; a spindle head supported for vertical movement along a column of the machining center, a spindle rotatably mounted in the spindle head and having a tool-receiving end for receiving therein individual tools stored in the tool magazine, a draw-bar disposed for axial movement within the spindle between a tool-engaging position and a tool-disengaging position, the draw-bar having one end engagable with a tool received in the tool-receiving end of the spindle when the draw-bar is at its tool-engaging position, the draw-bar having another end extending axially beyond the spindle, elastic pressure means continously urging the draw-bar towards its tool-engaging position, a draw-bar actuating cam member fixed to the column and having an actuating surface, and a bell-crank lever mounted at a corner thereof for pivotal movement about a pivot mounted on the spindle head, the bell-crank having a cam member-engaging arm and a draw-bar-depressing arm, an end of the cam-member-engaging arm of the bell-crank lever being disposed for engagement with the cam member actuating surface upon upward movement of the spindle head so as to actuate the bell-crank lever to move about its pivot so that the draw-bar-depressing arm of the bell-crank lever depresses the draw-bar toward the tool-disengaging position thereof, the improvement comprising: an upper end surface member provided upon the other end of the drawbar; the drawbar-depressing-arm of the bell-crank lever being disposed above the upper end surface member of the draw-bar; a spherical depressing member directly attached at an under surface of the draw-bar-depressing arm of the bell-crank lever, for point contact with the upper surface member of the draw-bar so as to depress the draw-bar in response to arc movement of the draw-bar-depressing arm of the bell-crank lever by the cam member actuating surface; a spring member arranged between the spindle head and the bell-crank lever adjacent the pivot thereof for urging the bell-crank lever in a direction about the pivot thereof to separate the spherical depressing member form the axially extended draw-bar end so as to hold apart the draw-bar-depressing arm of the bell-crank lever from draw-bar while the bell-crank cam member-engaging end is disengaged from the cam member actuating surface; and an adjustable limiting member disposed between the spindle head and the bell-crank lever ajdacent the pivot thereof, for limiting excessive pivoting of the bell-crank lever under urging of the spring member when the bell-crank cam-engaging end is disengaged from the cama member actuating surface.