Abstract: A sewing machine having a torsion spring coupling between drive and machine shaft. An engageable catch pawl acts on a stop element connected to the drive, which stop element is connected to the drive side of the coupling spring of the drive. If the catch pawl is engaged with the machine in operation and the stop element is blocked, the coupling spring is released and hence the coupling disengaged. The motor may then run down while the motor shaft is stopped resiliently in a predetermined position via the coupling spring which simultaneously the coupling spring prevents excessive forces from occurring due to inertia and excess stressing. Hence this construction permits the motor to be stopped rapidly from full operation with simple means.

Abstract: A mechanism for coupling and uncoupling a driven rotatable drive wheel from a rotatable shaft, particularly, the arm shaft of a sewing machine from its associated drive wheel in order to spool up the lower thread, comprises a rotatable shaft which has an annular collar portion which is frictionally engageable by a drive wheel which is freely rotatable on the shaft. The drive wheel is continuously driven from a drive, such as a belt, and it may be urged into engagement with the collar by means of a nut which is threaded onto the end of the shaft. The arrangement includes a stop disc which has a cam surface which is engageable with a stop defined on the nut end face in a recess thereof. The cam surface and the stop define a cam structure which permits rotation of the nut so as to permit frictional engagement of the drive wheel with the shaft collar for driving the shaft and the disengagement thereof by rotation of the nut in a reverse direction.