The Twisted-Shaft Needle Rocker: A Straight Push That Swings the Needle, Then Holds It Still

A sewing machine's curved needle or looper must swing through its arc at the right moment, then stand still while the other needle passes, and a crank or cam that does this is noisy and wears. W. O. Grover of Boston received US 21,670, dated 5 October 1858, for "actuating a curved needle, looper, or hooker-on having an interrupted vibratory motion by means of the combination of an irregular-shaped spiral shaft with a reciprocating driver". The needle's shaft is flat at its top and bottom and cut between them like an American auger or gimlet; a driver moving up and down carries pieces of watch or clock spring that bear on the shaft, so it turns while the springs pass the screw and rests while they lie on the flats. Layers of rawhide or leather between the springs quiet the rattle and hold oil. This rung works out the swing and the pause, then twists a flat bar with straight ends, mounts it with a sliding driver, and counts the swing and the rest.