Apparatus for preventing circumferential overspeeding of a grinding wheel

In an apparatus for preventing circumferential overspeeding of a grinding wheel in a grinding machine having a wheel head, a wheel spindle rotatably supported upon said wheel head for mounting said grinding wheel and a driven pulley at both ends thereof, a drive motor adapted to have first and second drive pulleys alternatively mounted thereon, said second drive pulley having a diameter larger than that of said first drive pulley, and belt means for drivingly connecting said drive pulley on said drive motor with said driven pulley, the improvement comprising:

• means for providing slot means extended radially of said grinding wheel and defining thereon retraction and forward positions corresponding, respectively, to first and second diameters of said grinding wheel;
• a cover device for accommodating said drive pulley on said drive motor, said driven pulley and said belt means;
• a slide plate guided by said cover device and slidable radially of said drive pulley on said drive motor;
• a first member perforated through said slot means to be opposed to the circumferential surface of said grinding wheel;
• a second member engaged with said slide plate to be moved radially of said drive pulley on said drive motor together with said slide plate;
• a link mechanism provided upon said wheel head for linking said first member with said second member;
• and
• a restraining member provided upon said slide plate to be moved by said link mechanism into such a space as to be occupied by said second drive pulley on said drive motor when said first member is retracted from said forward position to said retract position within said slot means.