Abstract: Apparatus as described for centering a collet chuck relative to the longitudinal axis of a dop arm for a gem faceting machine. The apparatus includes a socket mounted to the dop arm and a plug slidably received within an open longitudinal bore formed within the socket. The plug mounts a collet chuck. Two longitudinally spaced sets of screws extend radially into the socket. The individual screws of the two sets can be turned against the plug to adjust the collet chuck into a secure precise coaxial relation with the dop arm axis.

Abstract: A mill for grinding flour and the like. Two flat grinding discs are mounted in opposed relation to one another. One disc is non-rotatably mounted with respect to the housing that supports it, while the other is rotated by a motor drive. The non-rotatable disc coaxially supports the shaft for the rotatable disc. The non-rotatable disc can be adjusted axially to vary the spacing between the grinding surfaces of the respective discs. Provision is also made for yieldable movement between the discs in response to the grinding load.

Abstract: An adjustable faceting head support assembly having an upright mast with a longitudinal open groove that receives an elongated vertical lead screw. The lead screw is mounted within the groove about an axis parallel to the axis of the mast. A collar assembly encompasses the lead screw and mast for longitudinal sliding movement along the mast. A half nut mechanism provided on the collar enables selective engagement and disengagement with the lead screw. An adjusting knob at an upper end of the lead screw allows for precise rotation of the lead screw to locate the faceting head at a precise position with respect to a lap surface when the half nut is engaged with the lead screw. When the half nut is disengaged from the lead screw, the faceting head may be moved freely along the mast axis, permitting one to quickly position the faceting head over the lap.