Abstract: The subject action is a modification of the traditional upright action. The traditional jack spring is eliminated. Its function is assumed by a jack/repetition spring, which is a compression spring adjustably mounted between the jack near the end that engages the hammer butt and a pilot attached to a threaded shaft through the back stop portion of the hammer assembly. The hammer return spring mounting enables adjustment of the range of force applied by the spring to the hammer. The force range magnitude is such that the hammer return torque is commensurate to the torque that would be applied by gravity if the hammer shank were mounted horizontally instead of vertically. The operating force of the jack/repetition spring is related to that of the hammer return spring in such a way that re-engagement of the jack with the hammer butt is assured before hammer return beyond the back-checked point.

Abstract: The subject action is a modification of the traditional upright action. The traditional jack spring is eliminated. Its function is assumed by a jack/repetition spring, which is a compression spring adjustably mounted between the jack near the end that engages the hammer butt and a pilot attached to the back stop portion of the hammer assembly. The hammer return spring mounting enables adjustment of the range of force applied by the spring to the hammer. The force range magnitude is such that the hammer return torque is commensurate to the torque that would be applied by gravity if the hammer shank were mounted horizontally instead of vertically. The operating force of the jack/repetition spring is related to that of the hammer return spring in such a way that re-engagement of the jack with the hammer butt is assured before hammer return beyond the back-checked point.