MACHINE TOOL

摘要

A surface grinding machine wherein a tool holder is mounted on an upright feed screw which is in mesh with a rotary spindle nut. The latter is held against axial movement in the column of the grinding machine and is normally driven by a torque transmitting unit having an endless toothed belt trained over a first pulley which is coaxial with the nut and a second pulley mounted on the output shaft of an electric motor. A gear train is installed in parallel with the torque transmitting unit to prevent automatic lowering of the tool holder when the belt breaks. The gear train has a first gear coaxial with the first pulley, a second gear coaxial with the second pulley and an additional gear meshing with the first and second gears. The tension of the belt is monitored by a detector which transmits a signal when the belt breaks, and such signal is used to immediately arrest the motor.