Screw thread tap grinding

Screw thread tap grinding apparatus for grinding form relief on the thread form of tap workpieces comprising a base structure mountable in a grinding machine in relation to a thread grinding wheel of the latter for relative traverse of said base structure and grinding wheel;

• a cradle carrying headstock and tailstock, means for rotatably receiving a tap workpiece between a driving center spindle of the headstock and a center of the tailstock whereby the axis of the headstock center spindle and tailstock center and of a said tap workpiece received thereby is parallel to the axis of rotation of a said grinding wheel, said cradle being pivotally mounted on said base structure about an axis parallel with said axis of the headstock center spindle and tailstock center for lateral oscillation of the cradle and of a said tap workpiece carried thereby parallel to said axes and relative to a said grinding wheel;
• a follower directly carried by said cradle;
• bearing support fixedly mountable in the grinding machine in relation to the base structure;
• a cam rotatably carried by said bearing support about an axis parallel with the axis of the headstock center spindle and tailstock center and of the pivotal axis of the cradle and directly co-operating with said follower, said cam being of a form for imparting said lateral oscillation to the cradle in effecting thread form relief of a said tap workpiece;
• gear drive means for driving the cam from a driving shaft of the grinding machine and consisting of at least a driving gear wheel directly drivable from said driving shaft and a driven gear wheel rotationally fast with the cam and providing a gear ratio for driving the cam at a speed of rotation in relation to that of the headstock center spindle having regard to the number of threaded lands of a said tap workpiece driven by said headstock center spindle, said gear drive means being independent of the pivotal axis of the cradle;
• and a floating center coupling interposed between and drivingly connecting the driving gear of the gear drive means directly to the headstock driving center spindle for through drive of the latter from the grinding machine driving shaft and permitting said lateral oscillation of the cradle relative to said shaft during said drive.