Improvements in Cutlery Grinding Machines

23,285. Joy, C. L. Nov. 13. Screw-and-nut mechanism.-In a cutlery grinding-machine, the reciprocation of the table carrying the tool to be ground is obtained from a continuously-rotating screw. The screw 13 is driven from a pulley 14 and carries two screw-threads, one a coarse left-hand thread 13 and the other a finer right-hand thread 13. The table 15 carries a pivoted lever 34, the ends of which are formed with threads to fit the screws 13, and are alternately depressed into contact with them. The difference in the pitch of the screws gives a quick return motion. The end 34 is depressed on to the finer screw 13 by the rod 38 operated by a pivoted lever 36 above the table 15. The lever 34 is held in this position during the grinding operation by a pivoted catch 39, which is maintained in position by the spring 40. When the table reaches the end of its journey, a stop 41 releases the catch 39 and the spring 42 forces the end 34b of the lever 34 on to the coarser screw 13. If the spring fails to depress the lever, the bevelled face of a screwed stop acts on a pin projecting laterally from the end of the lever and ensures its contact with the screw. When the table has reached the end of the return journey, the end 34 of the lever 34 rests on the plain surface 13 of the spindle 13, giving an interval of rest while a fresh knife &c. is being inserted in the holder. The stop 39 can be operated manually at any position of the table.