Spring collet for machine tools

Spring collet for use within a spindle assembly of machine tools and automatic lathes, configured for machining high-precision parts, wherein:

• the spring collet has an axis and concentrically aligned thereto, a variable central axial opening adjustable to a first open position and to a second closed position, for respectively releasing and clamping a workpiece, and spring collet having at least two grooves, where each one of the two grooves has two mutually opposite faces, and
• a collar extending concentrically outward from the spring collet, and having a tapering surface against which rests a corresponding face of a sleeve operable for translating forth and back along a limited axial course length, to reversibly dispose the variable central axial opening, respectively, in the open and in the closed position, comprising:
• at least one portion of each one of the at least two grooves having a gap opening when the spring collet is in the open position,
• at least a portion of two mutually opposite faces of the at least two grooves abut against each other when the spring collet is in the closed position and grips the workpiece with a predetermined clamping force, wherein
• an axial length λ of the collar being retained within a length interval whose lower and upper limits are about, respectively, twice and five times the axial course length, and
• the tapering surface being inclined by about 45° relative to the axis of the spring collet.