1354450 Chucks GLEASON WORKS 9 Nov 1972 [6 Dec 1971] 51805/72 Heading B3B A rotary work holding apparatus comprises a body 10 attached to a spindle 14 and including a front face 20 against which a ring workpiece, e.g. a bevel gear ring G, is seated, and a central bore 23 extending therethrough; cylindrical hub means 22 projecting from the front face, the axes of the bore and hub means being coincident with the axis of rotation of the apparatus; a draw bolt 26 slidable through the hub means and having a head spaced from the hub means; and an annular arbor member seated between the head and hub means and adapted to expand to grip the bore of the workpiece G upon axial motion of the draw bolt 26 with respect to the body 10; wherein said arbor member is dish shaped and comprises a collar 28 surrounding a central bore which receives the said head, an elongated shoulder portion 32 inclined from the collar 28 to an outer periphery 34, and a flange 36 extending from the outer periphery 34 and including an outer cylindrical work gripping surface 38 and a tapered inner face 40; and wherein said hub means includes a tapered surface 24 for mating engagement with the tapered inner face of the flange on rearward motion of the draw bolt. The tapered surfaces 24, 40 ensure area clamping at the gripping face 38 rather than line contact with the workpiece. The arbor member has radial slots filled with a rubber or plastics webbing material and air pressure is fed into a chamber 56 and out of channels 54, 53 to prevent contamination by dirt or abrasive compounds. Springs 42 bias the hub means 22 away from the front face of the body 10 so that during clamping the workpiece G is initially clamped internally and then pulled on to the front face 20.