Abstract: In a plying machine at least two original threads are taken from run-off spools and are together wound as a doubled thread over a plying spool. The machine has a magazine for replacing one of the run-off spools with at least one reserve spool. A thread watcher can sense the presence and absence of the original threads along predetermined respective paths and can provide in response thereto a watcher signal. A common cutter can concurrently cut the original threads. The machine has a knotter for binding together the original threads and the doubled thread. The knotter is positioned, at least when binding, at at least one predetermined position on the machine. A plurality of guides, each having a thread grasper, can provide the original threads and the doubled thread to the knotter. Also included is a controller coupled to the cutter, to the knotter and to at least one of the guides for automatically operating them in response to the watcher signal.