Chuck for a machine tool

A chuck for a machine tool comprising a scroll board of generally a cylindrical main body having a concentric bore therein with a scroll groove being formed on one end surface thereof and having a number of radial slots formed through said cylindrical main body so as to open in said end surface, a corresponding number of slider blocks each radially movably received within each of said radial slots and having a number of arcuate grooves on the exposed surface so as to be in communication with said scroll groove of said scroll board, each said slider block being provided on the radially inner end with a radial elongation which is formed on the radial inner end with an engaging element, a cup-shaped cover board having a cylindrical body and an annular cover plate closing one of open ends thereof so as to rotatively receive said scroll board within the space defined by said cylindrical body and said cover plate, whereby said annular cover plate confronts said scroll groove of said scroll board, said annular cover plate being formed with a corresponding number of radial slots therethrough, a corresponding number of claws each radially movably received within said slots, respectively, of said annular cover plate of said cover board and provided on the under surface with a number of arcuate projections so as to be in mesh with said scroll groove of scroll board, and a manipulating member having generally a cylindrical form and axially movably received within said bore of said scroll board and adapted to be moved by a suitable actuating means, said manipulating member being formed on its outer periphery with a corresponding number of engaging means each adapted to cooperate with said each of engaging elements of said slider blocks so as to move them radially when said manipulating member is moved axially.