Magnetic chuck

A magnetic device, especially a chuck for magnetic retention of workpieces, comprising:

• a stack of alternately magnetic and nonmagnetic plates defining an exposed upper surface and at least two exposed lateral surfaces adjoining said upper surface of a body, said stack extending longitudinally and said plates being perpendicular to the longitudinal dimension of said stack, said plates each having at least one opening and said openings being aligned along said stack to form at least one longitudinally extending hollow,
• a first magnetic assembly received in said hollow and comprising at least one stack of alternating permanent magnets and pole pieces with the pole pieces of said first assembly alternating in magnetic polarity;
• a second magnetic assembly mounted in said body and comprising at least one stack of permanent magnets for creating magnetic polarities alternating along said second assembly, said pole pieces corresponding in thickness measured along the longitudinal dimension generally to the thicknesses of said plates, the magnetic pitch of said first assembly being equal to the distance between corresponding portions of successive pole pieces;
• and
• means mounted on said body engaging one of said assemblies for displacing same longitudinally through a distance at least equal to said magnetic pitch thereby shifting selectively between an ON position in which a magnetic field appears at each of said surfaces to affix a workpiece thereto and an OFF position in which the magnetic field at said surfaces is substantially canceled, the other of said assemblies being fixed relative to said body.