Patent ID: 8419509

Claim:
A grinding machine comprising: a bed; a work table horizontally movable on the bed in a first direction; a workpiece drive and support mechanism mounted on the work table for supporting a workpiece to be rotatable about an axis extending in the first direction; a first feed mechanism for feeding the work table on the bed in the first direction; a grinding wheel table horizontally movable on the bed in a second direction intersecting with the first direction; a swivel device mounted on the grinding wheel table, the swivel device comprising a support base, a swivel head arranged on the support base to be turnable about a swivel shaft and having a plurality of tool spindles, wherein axes of the plurality of tool spindles are arranged in a single plane and wherein the single plane extends perpendicular to the axis of the swivel shaft, the swivel device further comprising an annular space portion formed between the support base and the swivel head in coaxial relation with the swivel shaft, wherein the single plane perpendicular to the axis of the swivel shaft crosses the annular space portion at about a mid portion of the annular space portion in the axial direction of the swivel shaft, and a direct drive motor comprising a rotor and a stator being built in the annular space portion for driving the swivel head to turn about the swivel shaft, the direct drive motor being arranged so that the plane perpendicular to the axis of the swivel shaft extends across about the centers of the rotor and the stator in the axial direction of the swivel shaft, wherein the support base is fixed on the grinding wheel table and wherein the swivel shaft extends vertically so that the swivel head is horizontally turnable about the swivel shaft; a second feed mechanism for feeding the grinding wheel table in the second direction; and first and second wheel spindle support mechanisms provided on first and second side surfaces of the swivel head and respectively supporting the tool spindles with first and second grinding wheels mounted on the tool spindles being rotatable about respective axes of the tool spindles in the single plane perpendicular to the axis of the swivel shaft.