Abstract: A machine for operating on sheet stock workpieces having stock grippers mounted on a work positioning carriage for moving the sheet stock workpiece along first and second relatively transverse paths in the plane of the stock to position the workpiece at predetermined positions relative to the machine tools. Work grippers are mounted on the work positioning carriage for adjustment relative to the carriage when the work grippers are released and the work grippers are automatically clamped against movement relative to the carriage when the work grippers are actuated to grip the stock.